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41396 Publications

Rayleigh-Bénard Convection in Liquid metal under Influence of Vertical Magnetic Fields

Schindler, F.; Zürner, T.; Vogt, T.; Eckert, S.; Schumacher, J.

Conference (Lecture):

American Physics Society (APS) DFD meeting 2019 Seattle

In the presented Rayleigh-Bénard convection experiments the turbulent 3d-
flow of the liquid gallium-indium-tin alloy is investigated by use of ultrasound
Doppler velocimetry, temperature and contactless inductive flow tomography
measurements. We reconstruct for the first time near-wall as well as bulk
flow, momentum and heat transport as well as long-term behaviour of the large-scale liquid
metal flow at a low Prandtl number of 0.029 and high Rayleigh numbers up
to 6 · 10e7. Also the influence of a strong magnetic field on the turbulent liquid metal is investigated. The results of the
experiments are compared to direct numerical simulations and other experiments. These are also
considered for the interpretation of the measured turbulence statistics.
Our experiments aim to provide a deeper understanding of the turbulent
convection and its interaction with magnetic fields in turbulent low Prandtl number
flows as those in molten steel, aluminium or geo- and astrophysical flows.

Keywords: Rayleigh-Bénard convection; magnetohydrodynamics; low Prandtl number; liquid metal; ultrasound velocimetry

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Permalink: https://www.hzdr.de/publications/Publ-30444
Publ.-Id: 30444


Analysis, design and optimization of compact ultra-high sensitivity coreless induction coil sensors

Ratajczak, M.; Wondrak, T.

We require a compact magnetic field measurement system that is able to measure alternating magnetic flux densities in the nanotesla range on the background of signals with constant amplitudes of some hundred millitesla. The signal of interest has a frequency of a few Hertz and must be measured with an amplitude error smaller than 0.1% and a phase error no larger than 10⁻¹ deg. For this we present theoretical and experimental analyses of absolute and first order gradiometric induction coil sensors with sensitivities larger than 500 V/T/Hz and diameters of 28 mm. From their equivalent circuits, we derive the associated complex-valued transfer functions and fit these to calibration measurements, thereby determining the value of the equivalent circuit components. This allows us to compensate their non-linear frequency-dependent amplitude and phase behaviour. Furthermore, we demonstrate the optimization of coils based on Brooks' design of equal squares in the adaptation by Murgatroyd, which maximizes the inductance (and thereby most likely the sensitivity) of the coils. Finally, we design a new coil with a diameter of 74 mm and a sensitivity of 577 V/T/Hz with an analytically predicted equivalent magnetic field noise of around 40 pT/√Hz in the 1 Hz frequency range, which is then confirmed by measurements on the manufactured prototype.

Keywords: magnetic field measurement; induction coil; gradiometric coil; contactless inductive flow tomography

Permalink: https://www.hzdr.de/publications/Publ-30443
Publ.-Id: 30443


Rayleigh-Bénard Convection in a Vertical Magnetic Field at Low Prandtl Number

Schindler, F.; Zürner, T.; Vogt, T.; Eckert, S.; Schumacher, J.

11th PAMIR International Conference- Fundamental and Applied MHD July 1-5, 2019, Reims, EVEM France

The present work shows the experimental realisation of three-dimensional
magnetoconvection studies at Rayleigh numbers between 10e6 and 6 · 10e7 and Hartmann
numbers up to 1000 in a Rayleigh-Bénard convection cell. The fluid in the cell is the
GaInSn metal alloy with a low Prandtl number of 0.029. The flow is investigated using
thermocouples and ultrasound-Doppler-velocimetry. The change of the Nusselt number
with increasing Hartmann number is studied and presented. Experimental results are
compared to other experiments and simulations.

Keywords: liquid metal; low Prandtl number; Rayleigh-Bénard magnetoconvection; vertical magnetic Field

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Permalink: https://www.hzdr.de/publications/Publ-30441
Publ.-Id: 30441


X-ray radiographic visualization of bubbly flows injected by a top submerged lance in a liquid metal layer

Akashi, M.; Keplinger, O.; Anders, S.; Reuter, M.; Eckert, S.

We report on laboratory experiments focusing on bubbling phenomena arising from gas injection through a top submerged lance (TSL) in a liquid metal layer. Visualization was performed in the eutectic alloy GaInSn using X-ray radiography. Argon bubbles were injected through the nozzle positioned at three different submergence depths. Essential parameters such as the bubble size, bubble shape, detachment frequency or the two-dimensional gas distribution in the flat vessel were obtained by image processing. The results show that the deep position of the submerged lance causes an asymmetric large-scale circulation inside the fluid vessel. Bubble detachment frequencies were calculated by Fast Fourier Transformation from fluctuations of the image intensity in the vicinity of the nozzle injection point. This frequency does not show strong variations with respect to changes of the gas flow rate and the submergence depth of the nozzle. An increasing gas flow rate results in an increasing two-dimensional projected bubble area and the occurrence of a significant number of small bubbles being trapped by the strong fluid flow in the liquid metal layer.

Keywords: Two phase flow; Liquid metal; Top submerged lance

Related publications

  • Lecture (Conference)
    17th Multiphase Flow Conference and Short Course, 11.-15.11.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30440
Publ.-Id: 30440


Low Prandtl Number Rayleigh-Bénard Convection in a Vertical Magnetic Field

Schindler, F.; Zürner, T.; Vogt, T.; Eckert, S.; Schumacher, J.

Lecture (Conference)

11th PAMIR International Conference- Fundamental and Applied MHD July 1-5, 2019, Reims, EVEM France

We are investigating turbulent Rayleigh-Bénard convection in liquid metal under the
influence of a vertical magnetic field. Utilizing a combination of thermocouple (TC) and
ultrasound-Doppler-velocimetry (UDV) measurements gives us the possibility to directly
determine the temperature and velocity field, respectively. Further this gives us the
possibility to observe changes in the large-scale flow structure.
By applying magnetic fields to the liquid metal convection, we quantified changes of heat
and momentum transport in the liquid metal alloy GaInSn. The experimental results of our
setup agree well with theory findings and direct numerical simulations of the dynamics in
our convection cell. The requirement of large computing power at these parameters makes
it hard to simulate long-term dynamics with time scales from minutes to several hours. Thus
to investigate slow developing dynamics like sloshing, rotation, or deformation of the large-
scale flow structure model experiments are indispensable.
We demonstrate the suppression of the convective flow by a vertical magnetic field in a
cylindrical cell of aspect ratio 1. In this setup Rayleigh numbers up to 6·107 are
investigated. The flow structure at low Hartmann numbers is a single roll large scale
circulation (LSC). Increasing the Hartmann number leads to a transition from the single-roll
LSC into a cell structure. An even stronger magnetic field supresses the flow in the center
of the cell completely and expels the flow to the side walls.
Even above the critical Hartmann numbers corresponding to the Chandrasekhar limit for
the onset of magnetoconvection in a fluid layer without lateral boundaries we still observe
remarkable flows near the side walls. The destabilising effect of the non-conducting side
walls was predicted by theory and simulations, and is here for the first time experimentally
confirmed.

Keywords: Rayleigh-Bénard-Convection; Magnetohydrodynamic; low Prandtl Number; liquid metal; Ultrasound velocimetry

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Permalink: https://www.hzdr.de/publications/Publ-30439
Publ.-Id: 30439


CFD Modeling of Top-Submerged-Lance Argon injection in liquid metal

Obiso, D.; Sebastian, K.; Akashi, M.; Eckert, S.; Reuter, M.

The present paper focuses on the application of CFD techniques to investigate the Top-Submerged-Lance (TSL) gas injection in liquid metal.
Previous works of the authors have shown that up- and down-scaling procedures based on the modi-fied Froude number have some shortcomings, as this approach does not take into account the interfa-cial and viscous forces. Indeed surface tension and dynamic viscosity of the smelting slags (σ = 0.4-0.5 N/m, μ = 0.2 Pa·s) are higher than the operating fluids that have been used in literature (water, par-affin oil), which have been used to study TSL injection in down-scaled furnaces.. In order to get closer to real systems, the authors study the TSL injection of Argon in a liquid metal.
An experimental campaign was carried out at the Magnetohydrodynamic Department of Helmholtz-Zentrum Dresden-Rossendorf (HZDR), where the eutectic alloy GaInSn was used as liquid phase. The alloy is liquid at room temperature, and X-Ray imaging is used to picture the multiphase flow in a qua-si-2D vessel (140x140x12 mm).
The aim of the present work is to demonstrate the applicability of CFD techniques to model multi-phase flows involving liquid metals, and validate the model using the data produced at HZDR. The commercial software ANSYS Fluent® was used together with the Volume of Fluid model to directly resolve the gas-liquid interphase. Some features of the flow, such as the void fraction distribution and bubble detachment frequency are tracked with CFD and compared to the experimental data. The ef-fect on the hydrodynamics of different operating conditions, such as the lance immersion depth is investigated.
The authors are currently extending the work to new geometries and operating conditions, in order to get a broader amount of data, useful for the validation of models and for the further understanding of the TSL injection.

Keywords: two phase flow; top submerged lance; liquid metal

Related publications

  • Lecture (Conference)
    10th Copper International Conference (COPPER 2019), 18.-21.08.2019, Vancouver, Canada

Permalink: https://www.hzdr.de/publications/Publ-30436
Publ.-Id: 30436


Epitaxial Mn5Ge3 (100) layer on Ge (100) substrates obtained by flash lamp annealing

Xie, Y.; Yuan, Y.; Wang, M.; Xu, C.; Hübner, R.; Grenzer, J.; Zeng, Y.-J.; Helm, M.; Zhou, S.; Prucnal, S.

Mn5Ge3 thin films have been demonstrated as promising spin-injector materials for germanium-based spintronic devices. So far, Mn5Ge3 has been grown epitaxially only on Ge (111) substrates. In this letter, we present the growth of epitaxial Mn5Ge3 films on Ge (100) substrates. The Mn5Ge3 film is synthetized via sub-second solid-state reaction between Mn and Ge upon flash lamp annealing for 20 ms at the ambient pressure. The single crystalline Mn5Ge3 is ferromagnetic with a Curie temperature of 283 K. Both the c-axis of hexagonal Mn5Ge3 and the magnetic easy axis are parallel to the Ge (100) surface. The millisecond-range flash epitaxy provides a new avenue for the fabrication of Ge-based spin-injectors fully compatible with CMOS technology.

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Permalink: https://www.hzdr.de/publications/Publ-30435
Publ.-Id: 30435


Experimental analysis of gas phase dynamics in a lab scale bubble column operated with deionized water and NaOH solution under uniform bubbly flow conditions

Kipping, R.; Kryk, H.; Hampel, U.

In this study we present an investigation on the impact of sparger configuration and fluid properties on the local gas phase dynamics for up to 17% total gas holdup. Experiments in a bubble column with 100 mm inner diameter were conducted with deionized water and NaOH solution of up to cNaOH = 32 mmol·l−1. Ultrafast X-ray computed tomography (UFXCT) was applied to obtain local hydrodynamic parameters, such as gas holdup distribution, bubble sizes and average bubble rise velocities. Radial gas holdup profiles show wall peaking, which is attributed to the uniform bubbly flow regime generated by the needle sparger used in this study. The addition of NaOH leads to similar gas holdup values but significant changes on local bubbly dynamics, such as bubble size distribution and axial gas phase velocity. The Sauter mean diameter was found to decrease with increasing concentration of NaOH, whereby the decrease is larger at higher gas flow rate.

Keywords: bubble column hydrodynamics; mono-dispersed bubbly flow; bubble size distribution; bubble rise velocity; electrolyte solutions; Ultrafast X-ray tomography

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Permalink: https://www.hzdr.de/publications/Publ-30434
Publ.-Id: 30434


Mmpxrt; X-ray spectrometer simulation code with a detailed support of mosaic crystals.

Smid, M.; Pan, X.; Falk, K.

This is a a newly developed ray tracing code called mmpxrt, dedicated to study and design x-ray crystal optics, with a special focus on mosaic crystal spectrometers. Its main advantage over other currently available ray tracing codes is that it includes detailed and benchmarked algorithm to treat mosaic crystals, especially HOPG and HAPG (Highly Oriented / Annealed Pyrolitic Graphite). The code is dedicated primarily to study crystal spectrometers, therefore their implementation is very straightforward, and the code has mostly automatic evaluation of their performance. It can, however, be used universally to study other crystal instruments, like monochromators, mirrors, and analyzers. The code is publicly available in HZDR's Gitlab, written in Python3 and is distributed as a Python library with test cases included.

Keywords: mosaic crystal; x-ray spectroscopy; ray tracing; Python3

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Permalink: https://www.hzdr.de/publications/Publ-30433
Publ.-Id: 30433


High-motility visible light-driven Ag/AgCl Janus microswimmers interacting with passive beads

Wang, X.; Baraban, L.; Misko, V. R.; Nori, F.; Formanek, P.; Huang, T.; Cuniberti, G.; Faßbender, J.; Makarov, D.

Visible light driven nano/micro swimmers are promising candidates for potential biomedical and environmental applications. However, the previously reported mean squared displacement (MSD) values are low, typically in the range of up to 200 µm2 (when measured over 10 s), even under the favourable UV light illumination.[1,2]
Here, we demonstrate Ag/AgCl-based spherical Janus micromotors that reveal an efficient propulsion under visible blue light illumination.[3] The Ag/AgCl-based micromotor can boost the MSD to a remarkable value of 3000 µm2 (over 10 s) in pure H2O, even when activated with blue light (λ = 450-490 nm). Furthermore, we show that Ag/AgCl-based Janus micromotors reveal efficient exclusion effect to their surrounding passive polystyrene (PS) beads in pure H2O.[4] Using numerical simulations of the Langevin equations, we gain a fundamental understanding not only the diffusion constants, but also the system-specific interaction parameter between Janus motors and passive beads.
1. Ibele, M., et al., Angew. Chem. Int. Ed. 2009, 48, 3308.
2. Simmchen, J., et al., ChemNanoMat 2017, 3, 65.
3. Wang, X., et al., Small DOI: 10.1002/smll.201803613.
4. Wang, X., et al., Small 2018, 14, 1802537.

Keywords: Active Janus particles; exclusion interaction; passive beads; visible light‐driven micromotors

Related publications

  • Lecture (Conference)
    DPG Spring Meetings 2019, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30432
Publ.-Id: 30432


Programmed Magnetically-Triggered Ultrafast Soft Robots

Wang, X.; Ge, J.; Canon Bermudez, G. S.; Kosub, T.; Illing, R.; Wang, C.; Bischoff, L.; Faßbender, J.; Makarov, D.

Soft robots have been designed and developed to fulfil the demands of better deformability and adaptability to changing environment [1-2]. These soft robots could be made of various stimuli responsive materials that can be actuated by magnetic field [3], light [4], temperature [5], electric fields [6], chemicals [7], pressure [8], etc. In contrast to other actuation mechanisms, magnetic fields are appealing for numerous application scenarios (e.g. environmental, biological, medical), where the benefits stem from their long-range penetration, easy accessibility, and controllability [2]. Very recently, there are already impressive demonstrations of magnetically triggered millimetre- and centimetre- scaled soft robots performing multimodal locomotion [9] and complex 3D actuations [10]. However, their thick and bulky bodies [9-10] challenge themselves to reveal better performances for specific implantations which require more, for instance, high actuation speed, and reversible large-scale actuation amplitude by a rather low magnetic field.

Here, we present an ultrathin (7-100 μm) and lightweight (1.2-2.4 g/cm3) soft robot that can be actuated in a tiny magnetic field of 0.2 mT reaching full actuation amplitude with a reaction time of 10 ms only. By programming the foils into different geometries, these soft robots are readily used for multifunctional nature-mimicking motion with a magnetic coil or a permanent magnet, such as a quick fly gripping and releasing, complex fast human cross-clapping mimicking, etc.

[1] D. Rus et al., Nature 521, 467 (2015)
[2] L. Hines et al., Adv. Mater. 29, 13 (2017)
[3] J. Y. Kim et al., Nature materials 10, 747 (2011)
[4] J. Deng et al., J. Am. Chem. Soc. 138, 225 (2016)
[5] Y. S. Kim et al., Nature Materials 14, 1002 (2015)
[6] T. Mirfakhrai et al., Materials Today, 10, 30 (2007)
[7] Q. Zhao et al., Nature communications 5 (2014)
[8] SA. Morin et al., Science, 337, 828 (2012)
[9] W. Hu et al., Nature, 554, 81(2018)
[10] Kim. Y, et al., Nature, 558, 274 (2018)

Keywords: Soft robots; magnetic field; ultrafast actuation

Related publications

  • Lecture (Conference)
    2019 MRS Spring Meeting & Exhibit, 22.-26.04.2019, Phoenix, Arizona, USA

Permalink: https://www.hzdr.de/publications/Publ-30431
Publ.-Id: 30431


Investigation of particle dynamics and solidification in two phase system by neutron radiography

Baranovskis, R.; Sarma, M.; Ščepanskis, M.; Beinerts, T.; Gaile, A.; Eckert, S.; Räbiger, D.; Lehmann, E. H.; Thomsen, K.; Trtik, P.

We investigate directional solidification of the melt with solid inclusions by means of neutron radiography (NR). As NR is a non-invasive imaging technique, the results, for the first time, reveal the particle trapping in the solidifying melt at macro scale. It is shown that particle solidification in volume can be achieved when liquid and solid phases form mushy zone. Experiments were performed using a rectangular vessel containing tin which was electromagnetically stirred and directionally solidified. Information about the recirculating flow was gathered by tracing 355-500 μm gadolinium (Gd) particles which visualize the flow field and phase composition in any given time. The findings show that metallurgical challenges, e.g. stirring and homogenously dispersing ceramic reinforcement material in MMC, could be solved by applying electromagnetic treatment while melt is in semi-solidus state.

Keywords: Neutron radiography; particle trapping; directional solidification; mushy zone

  • Contribution to proceedings
    11th Pamir International Conference Fundamental and Applied MHD, 01.-05.07.2019, Reims, France
  • Magnetohydrodynamics 56(2020)1, 43-50
    DOI: 10.22364/mhd.56.1.4
    Cited 4 times in Scopus

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Permalink: https://www.hzdr.de/publications/Publ-30430
Publ.-Id: 30430


Pulsed magnetic field, high pressure and FIB microstructures - a powerful combination for studies of unconventional metals

Helm, T.

Für diesen Vortrag hat keine inhaltliche Kurzfassung vorgelegen.

  • Invited lecture (Conferences)
    J-Physics Conference, 18.-21.09.2019, Kobe, Japan

Permalink: https://www.hzdr.de/publications/Publ-30428
Publ.-Id: 30428


FIB microstructures and experiments under extreme conditions

Helm, T.

Für diesen Vortrag hat keine inhaltliche Kurzfassung vorgelegen.

  • Invited lecture (Conferences)
    LNCMI - Solid State Physics Seminar, 18.04.2019, Grenoble, France

Permalink: https://www.hzdr.de/publications/Publ-30427
Publ.-Id: 30427


Effect of chemical and hydrostatic pressure on the coupled magnetostructural transition of Ni-Mn-In Heusler alloys

Devi, P.; Salazar Mejia, C.; Caron, L.; Singh, S.; Nicklas, M.; Felser, C.

Ni-Mn-In magnetic shape-memory Heusler alloys exhibit generally a large thermal hysteresis at their firstorder martensitic phase transition which hinders a technological application in magnetic refrigeration. By optimizing the Cu content in Ni2CuxMn1.4−xIn0.6, we obtained a thermal hysteresis of the martensitic phase transition in Ni2Cu0.2Mn1.2In0.6 of only 6 K. We can explain this very small hysteresis by an almost perfect habit plane at the interface of martensite and austenite phases. Application of hydrostatic pressure does not reduce the hysteresis further, but shifts the martensitic transition close to room temperature. The isothermal entropy change does not depend on warming or cooling protocols and is pressure independent. Experiments in pulsed-magnetic fields on Ni2Cu0.21.2In0.6 find a reversible magnetocaloric effect with a maximum adiabatic temperature change of −13 K.

Permalink: https://www.hzdr.de/publications/Publ-30426
Publ.-Id: 30426


Fermi surface investigation of the filled skutterudite LaRu4As12

Klotz, J.; Götze, K.; Lorenz, V.; Prots, Y.; Rosner, H.; Harima, H.; Bochenek, L.; Henkie, Z.; Cichorek, T.; Sheikin, I.; Wosnitza, J.

Of all stoichiometric filled-skutterudite superconductors, LaRu4As12 has the highest critical field and temperature. Here we report on a detailed Fermi-surface investigation of LaRu4As12 by means of de Haas–van Alphen measurements and density-functional-theory calculations. We find evidence for a nearly spherical and a multiply connected Fermi-surface sheet. The different effective masses and mass enhancements for the two sheets support two-band superconductivity, which was inferred from previous specific-heat measurements. Furthermore, quantum oscillations persist as well in the superconducting phase. We use two models to describe the additional damping, yielding energy gaps differing by a factor of 5.

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Permalink: https://www.hzdr.de/publications/Publ-30424
Publ.-Id: 30424


Focused-ion-beam assisted micropatterning for experiments under extreme conditions

Helm, T.

Für diesen Vortrag hat keine inhaltliche Kurzangabe vorgelegen.

  • Invited lecture (Conferences)
    Helmholtz MML-Workshop, 13.-15.02.2019, Dresden, Deutschland
  • Invited lecture (Conferences)
    EMFL User Meeting, 25.06.2019, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-30423
Publ.-Id: 30423


Topological Two-Dimensional Polymers

Springer, M.; Liu, T.-J.; Kuc, A. B.; Heine, T.

There are around 200 two-dimensional (2D) networks with different topologies. The structural topology of a 2D network defines its electronic structure. Including the electronic topological properties, it gives rise to Dirac cones, topological flat bands and topological insulators. In this Tutorial Review, we show how electronic properties of 2D networks can be calculated by means of a tight-binding approach, and how these properties change when 2nd-neighbour interactions and spin-orbit coupling are included. We explain how to determine whether or not the resulting electronic features have topological signatures by calculation of Chern numbers, Z2 invariants, and by the nanoribbon approach. This tutorial gives suggestions how such topological properties could be realized in explicit atomistic chemical 2D systems made of molecular frameworks, in particular in 2D polymers, where the edges and vertices of a given 2D net are substituted by properly selected molecular building blocks and stitched together in such a way that long-range π-conjugations is retained.

Permalink: https://www.hzdr.de/publications/Publ-30422
Publ.-Id: 30422


Unidirectional tilt and enhancement of the Walker limit for domain walls in stripes with Dzyaloshinskii-Moriya interaction

Pylypovskyi, O.; Kravchuk, V.; Volkov, O.; Faßbender, J.; Sheka, D.; Makarov, D.

Efficient manipulations of chiral textures like domain walls and skyrmions are crucial for the development of prospective spintronic devices [1-2]. Domain walls moving in stripes with perpendicular anisotropy and Dzyaloshinskii-Moriya interaction (DMI) exhibit a tilt resulting in a decrease of their maximal velocity [3]. Beside the direct current influence [3], the tilt is usually caused by in-plane fields [4] or an edge roughness [5]. In this work, we show that the domain wall tilt can appear as a result of competition of the in-plane anisotropy and DMI. We also describe the field-driven dynamics of the tilted domain wall.

We consider an infinitely long biaxial stripe with interfacing DMI (Fig. 1) and biaxial anisotropy. The first easy axis of anisotropy is perpendicular to the stripe plane and the second easy axis lies within the stripe plane and makes an angle α with the stripe axis. The shape anisotropy forces α=0, while α≠0 can appear due to other effects, e.g. exchange bias from underlying antiferromagnet. The second anisotropy rotates the in-plane magnetization inside the domain wall according to the in-plane easy axis direction. The optimum of the DMI energy is reached when the magnetization rotates perpendicularly to the domain wall plane. In stripes the energy balance between these two energy terms and the energy of the domain wall tension results in a unidirectional tilt by angle χ of the domain wall plane (χ=0 corresponds to the domain wall perpendicular to the stripe), determined by α. There is a metastable state of the wall, tilted into the opposite direction in a certain range of anisotropy and DMI values. This is related to the symmetry break between the two opposite directions of the magnetization rotation inside the domain wall due to the presence of a weak DMI. Furthermore, the dynamics of the domain wall in the presence of a biaxial anisotropy and DMI exhibits a symmetry break with respect to the magnetic field and the easy axis direction A. The domain wall reveals fast and slow motion regimes for the opposite signs of α. The slow regime is characterized by a smaller Walker field b and switch of the magnetization direction inside the domain wall in a certain field below b . The latter results in an increase of the domain wall speed. The velocity of the domain wall is inversely proportional to cos χ. The maximum of the Walker field corresponds to α≠0 (Fig. 2).

In conclusion, we describe a unidirectional tilt of a domain wall in a biaxial stripe with DMI, which appears at equilibrium without external magnetic field and demonstrate the enhancement of the Walker field and velocity [6]. The domain wall dynamics reveal fast and slow regimes depending on the orientation of the easy axis of the in-plane anisotropy and the applied magnetic field.

References: [1] K.-S. Ryu, L. Thomas, S.-H. Yang et al., Nat. Nanotech., Vol. 8, 527 (2013); [2] O. Pylypovskyi, D. Sheka, V. Kravchuk et al., Sci. Rep. Vol. 6, 23316 (2016); [3] O. Boulle, S. Rohart, L. Buda-Prejbeanu et al., Phys. Rev. Lett. Vol. 111, 217203 (2013); [4] C. Muratov, V. Slastikov, A. Kolesnikov et al., Phys. Rev. B. Vol. 96, 134417 (2017); [5] E. Martinez, S. Emori, N. Perez et al. J. Appl. Phys. Vol. 115, 213909 (2014); [6] O. Pylypovskyi, V. Kravchuk, O. Volkov et al., ArXiv, 2001.03408 (2020)

Keywords: magnetism; domain wall; Walker limit

  • Lecture (Conference)
    Intermag (Conference is cancelled due to COVID-19), 04.-08.05.2020, Montreal, Canada

Permalink: https://www.hzdr.de/publications/Publ-30421
Publ.-Id: 30421


Skyrmion states, engineered by curvature gradients

Pylypovskyi, O.; Makarov, D.; Kravchuk, V.; Gaididei, Y.; Saxena, A.; Sheka, D.

Skyrmions attract a special attention for spintronic and spinorbitronic devices by their unique static and dynamic properties [1]. The interplay between geometry and magnetization texture gives additional degrees of freedom in control of such topologically nontrivial patterns via geometry-induced anisotropy and Dzyaloshinskii-Moria interaction (DMI) in materials with easy-normal anisotropy [2-5]. It is sufficient for appearance of skyrmions and skyrmion lattices as a ground state on small curvilinear defects [6].

Here, we propose a new way to stabilize skyrmions and control their size via curvature gradient in a nanoindentation even without intrinsic DMI [7]. Our mathematical formalism also allows to describe planar films with inhomogeneous distribution of material parameters. We consider a thin membrane with easy-normal anisotropy and circular nanoindentation of a conic frustrum shape with inner and outer radii R and R , respectively. This geometry can be described by two principal curvatures, k and k , providing the whole information about geometry in the given point of the membrane. While k (r) is inversely proportional to the distance from origin r, k (r) has sharp peaks in points of the bend of the membrane. To compare textures in curved membranes and flat films we propose a projection of a surface of revolution to a plane, which reconstructs a skyrmion equation. The energy of the magnetic texture in projected coordinates obtains a curvature-modified anisotropy and two DMI terms, related to principal curvatures. In contrast to the planar case, the corresponding skyrmion equation is characterized not only by DMI coefficients itself, but also their spatial derivatives playing a role of the external driving force, proportional to d(k + k )/dr. The main consequences of the driving force are: (i) the ground state cannot be strictly normal to the membrane with nonconstant curvature; (ii) a gradient of k can result in stabilization of the Neel skyrmion of radius R or R (Fig. 1). Skyrmions, stabilized at the inner and outer bends, have the opposite chiralities. If the difference between R and R is large enough, both skyrmions can coexist forming a skyrmionium state with zero total winding number. In the limiting case of sharp bends, the minimal angle α of the indentation side for stabilizing topologically nontrivial textures equals 4L/R radians, with R being either R or R (α = 0 corresponds to a flat film) and L being a magnetic length. Numerical analysis of skyrmion stability is performed in a wide range of geometrical parameters (Fig. 2). It is shown that the strength and spatial localization of the DMI coefficient, associated with k , plays the main role in the pinning of topologically nontrivial textures and pinning strength is estimated to be hundredths of Kelvin for typical parameters of Co/Pt multilayers.

In conclusion, we propose a mathematical framework which allows us to describe magnetic nanomembranes with rotational symmetry and planar films with circular distribution of material parameters using the same apparatus. It uncovers two mechanisms of skyrmion stabilization, namely DMI-driven [8] and DMI gradient-driven [7]. The first one does not require the curvature gradients and lead to formation of small-radius skyrmions, while the second allows stabilization of large-radius skyrmions and skyrmionium states of the geometrically defined size.

References: [1] A. Fert, N. Reyren, V. Cros, Nat. Rev. Mater., Vol. 2, 17031 (2017); [2] R. Streubel, P. Fischer, F. Kronast et al., J. Phys. D: Appl. Phys. Vol. 49, 363001 (2016); [3] O. Pylypovskyi, V. Kravchuk, D. Sheka et al., Phys. Rev. Lett. Vol. 114, 197204 (2015); [4] Y. Gaididei, V. Kravchuk, D. Sheka, Phys. Rev. Lett. Vol. 112, 257203 (2014); [5] Y. Gaididei, A. Goussev, V. Kravchuk et al., J. Phys. A: Mat. and Theor. Vol. 50, 385401 (2017); [6] V. Kravchuk, D. Sheka, A. Kákay et al., Phys. Rev. Lett. Vol. 120, 067201 (2018); [7] O. Pylypovskyi, D. Makarov, V. Kravchuk et al., Phys. Rev. Appl. Vol. 10, 064057 (2018); [8] V. Kravchuk, U. Roessler, O. Volkov et al., Phys. Rev. B, Vol. 94, 144402 (2016).

Keywords: curvature; nanoindentation; magnetism

  • Lecture (Conference)
    Intermag (Conference is cancelled due to COVID-19), 04.-08.05.2020, Montreal, Canada

Permalink: https://www.hzdr.de/publications/Publ-30420
Publ.-Id: 30420


Exploring the applications of advanced geomorphic indices in statistically based landslide susceptibility models: a case study from Tajik Tien Shan and Pamir

Barbosa Mejia, L. N.; Andreani, L.; Gloaguen, R.

The identification of areas prone to landslides is essential to adapt the response and reduce the negative impact in affected regions. This is usually done using landslide susceptibility models, which give the likelihood of a landslide occurring in an area depending on the local terrain conditions and the location of known past events. Detailed databases covering different thematic groups such as geomorphology, hydrology, geology and land use are paramount in order to produce a reliable identification of susceptible areas. However, thematic data from developing countries are scarce and the situation is even worse in mountainous regions which are yet highly vulnerable to natural disasters such as landslides. As a result, susceptibility models often rely heavily on geomorphic parameters derived from DEMs. The three dominantly used variables include slope, aspect and curvature. While these variables are simple to compute and can be obtained from any GIS software, the geomorphological significance of the last two of them is often poorly justified as the window of observation (3×3 pixels) is too small to capture the morphometric signature of landslides or the overall morphology of an entire slope profile.

This study explores the use of advanced geomorphic indices as the main input for landslide susceptibility models. These indices have been often used in tectonic geomorphology to understand the relationship between surface processes and landscape evolution and can provide a useful way to characterize the topography in mountainous regions. Tested indices include surface roughness, local relief, topographic position index, elevation relief ratio, surface index and Eigen-based analysis of the landscape. The test area encompasses the mountainous areas in Tajikistan (SW Tien Shan and Western Pamir), where large magnitude historical landslides have been reported and studied. Landslide susceptibility maps with good predictive capabilities are obtained using different statistically based approaches such as logistic regression and random forest. First, we explored the spatial association between the variables and the landslide catalog. Then, the input variables are recursively selected for each model based on the spatial associations and the improvement in model performance. The best model is chosen based on its predictive capability, measured by the receiver operator curve (ROC) and its dispersion from the cross-validation. Our results suggest that landslide susceptibility modeling using advanced geomorphic indices as the primary source of thematic information is a viable approach. Measures of the relative importance of geomorphic variables used in the best models show that indices such as eigenvalues, local relief, surface roughness, slope, topographic position index and surface index contributed significantly to the models while commonly used aspect and curvatures had a limited impact. Also, the methodology we used is low cost and built on free and open source programs (R and Python), making it easily available for developing countries.

Keywords: Landslide susceptibility; morphometric indices; digital elevation model

  • Poster
    EGU2019, 10.04.2019, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-30417
Publ.-Id: 30417


Publishing - Licensing - Financing : 1. EU-Day at HZDR

Reschke, E.

What should you know about publishing within an EC project? Which license is the best for your publication? The presentation gives information about Open Access and financing of Articles Processing Charges (APC), licencing and the HZDR repositories ROBIS and RODARE.

Keywords: Open Access; Articles Processing Charges (APC); ROBIS; RODARE; Publishing; European Commission; Project publications; Licensing; Copyright; Hybrid journals; DEAL

  • Open Access Logo Lecture (others)
    1. EU-Day at Helmholtz-Zentrum Dresden-Rossendorf, 09.12.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30416
Publ.-Id: 30416


Functionalized DNA Origami Nanostructures for Molecular Electronics

Bayrak, T.; Ye, J.; Weichelt, R.; Reyes, A.; Eychmüller, A.; Samano, E.; Seidel, R.; Erbe, A.

The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications.1 Based on this technique, the precise positioning of metallic and semiconducting nanoparticles along DNA nanostructures can be achieved. In this study, various DNA origami nanostructures (nanomolds, nanotubes and nanosheets) are used as templates for the fabrication of nanoelectronic devices. To this end, gold nanoparticles, semiconductor quantum dots/rods are used in/on the DNA origami structures to create nanowires and transistor-like devices. In order to investigate the transport properties of the fabricated nanostructures, the wires are contacted using top-down methods. The DNA origami nanowires and transistors were electrically characterized from room temperature (RT) down to 4.2K.2 Temperature-dependent characterizations of wires were performed in order to understand the dominant conduction mechanisms. Some nanowires showed pure metallic behavior. Transistor like devices showed Coulomb blockade behavior at RT. The study shows that self-assembled DNA structures can be used for nanoelectronic patterning and single electron devices.

Related publications

  • Poster
    MML meeting From Matter to Materials and Life, 15.01.2019, Dreikönigskirche Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30415
Publ.-Id: 30415


Morphology Modification of Si Nanopillars under Ion Irradiation at Elevated Temperatures

Xu, X.; Heinig, K.-H.; Möller, W.; Engelmann, H.-J.; Klingner, N.; Gharbi, A.; Tiron, R.; Facsko, S.; Hlawacek, G.; Borany, J.

Ion beam irradiation of vertical nanopillar structures may be utilized to fabricate a vertical gate-all-around (GAA) single electron transistor (SET) device in a CMOS-compatible way. After irradiation of Si nanopillars (with a diameter of 35 nm and a height of 70 nm) by either 50 keV broad beam Si+ or 25 keV focused Ne+ beam from a helium ion microscope (HIM) at room temperature and a fluence of 2e16 ions/cm2, strong deformation of the nanopillars has been observed which hinders further device integration. This is attributed to ion beam induced amorphization of Si allowing plastic flow due to the ion hammering effect, which, in connection with surface capillary forces, dictates the final shape. However, plastic deformation can be suppressed under irradiation at elevated temperatures (investigated up to 672 K). Then, as confirmed by bright-field transmission electron microscopy, the substrate and the nanopillars remain crystalline and are continuously thinned radially with increasing fluence down to a diameter of 10 nm. This is attributed to enhanced forward sputtering through the sidewalls of the pillar and found in reasonable quantitative agreement with the predictions from 3D ballistic computer simulation using the TRI3DYN program.
This work is supported by the European Union’s H-2020 research project ‘IONS4SET’ under Grant Agreement No. 688072.

Related publications

  • Lecture (Conference)
    10th International Workshop on Nanoscale Pattern Formation at Surfaces (NanoPatterning 2019), 07.-10.07.2019, Surrey, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-30414
Publ.-Id: 30414


Integriertes Management und Publikation von wissenschaftlichen Artikeln, Software und Forschungsdaten am Helmholtz-Zentrum Dresden-Rossendorf (HZDR) : 1.Sächsische FDM-Tagung 2019, Dresden

Reschke, E.; Konrad, U.

Mit dem Ziel, das Publizieren von Artikeln, Forschungsdaten und wissenschaftlicher Software gemäß den FAIR-Prinzipien (https://www.go-fair.org/fair-principles/) zu unterstützen, wurde am HZDR ein integriertes Publikationsmanagement aufgebaut. Insbesondere Daten- und Softwarepublikationen erfordern die Entwicklung bedarfsgerechter organisatorischer und technischer Strukturen ergänzend zu bereits sehr gut funktionierenden Services im Publikationsmanagement. In der Zusammenarbeit mit Wissenschaftlern des HZDR und internationalen Partnern in ausgewählten Projekten wurde der Bedarf an Unterstützung im Forschungsdatenmanagement analysiert. Darauf aufbauend wurde schrittweise ein integriertes System von Infrastrukturen und Services entwickelt und bereitgestellt. In einer seit Mai 2018 gültigen Data Policy wurden die Rahmenbedingungen und Regelungen sowohl für wissenschaftliche Mitarbeiter als auch für externe Messgäste definiert. Im Vortrag wird auf die Erfahrungen im integrierten Publikationsmanagement für Artikel, Forschungsdaten und Forschungssoftware eingegangen und daraus resultierend werden die nächsten Aufgaben und Ziele entwickelt

Keywords: ROBIS; RODARE; Publikationsmanagement; Forschungsdaten; Forschungssoftware; publication management; research data; research software; FAIR; Open Access

  • Open Access Logo Invited lecture (Conferences)
    1. Sächsische FDM-Tagung, 19.09.2019, Dresden, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-30413
Publ.-Id: 30413


Towards a vertical nanopillar-based single electron transistor – a high-temperature ion beam irradiation approach

Xu, X.; Heinig, K.-H.; Engelmann, H.-J.; Möller, W.; Klingner, N.; Gharbi, A.; Tiron, R.; Facsko, S.; Hlawacek, G.; Borany, J.

The usage of ion beam irradiation on vertical nanopillar structures is a prerequisite for fabricating a CMOS-compatible, vertical gate-all-around(GAA) SET device. After either 50 keV broad beam Si+ or 25 keV focused Ne+ beam from a helium ion microscope (HIM) irradiation of the nanopillars (with diameter of 35 nm and height of 70 nm) at room temperature with a medium fluence (2e16 ions/cm2), strong plastic deformation has been observed which hinders further device integration. This differs from predictions made by the Monte-Carlo based simulations using the program TRI3DYN. We assume that it is the result from the ion beam induced amorphization of Si accompanied by the ion hammering effect. The amorphous nano-structure behaves viscously and the surface capillary force dictates the final shape. To confirm such a theory, ion irradiation at elevated temperatures (up to 672 K) has been performed and no plastic deformation was observed under these conditions. Bright-field transmission electron microscopy micrographs as well as Electron Beam Diffraction confirmed the crystallinity of the substrate and nanopillars after HT-irradiation. In addition, a steady thinning process of the nanopillars to a diameter of 10 nm has been observed at higher fluencies. As the original pillar diameter is comparable to the size of the collision cascade, instead of direct knock-on sputtering, enhanced forward sputtering through the sidewalls of the pillar is responsible for this effect. The relation between ion beam energy, flux and temperature with the observed thinning of the nanopillars has been studied experimentally and compared to TRI3DYN simulations. Such a reliable and CMOS-compatible process could serve as a potential downscaling technique for large-scale fabrication of nanopillar-based electronics.

Related publications

  • Lecture (Conference)
    The Second International Workshop of the PicoFIB Network, 13.02.2019, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-30412
Publ.-Id: 30412


Functionalized DNA Origami Nanostructures for Molecular Electronics

Bayrak, T.; Ye, J.; Weichelt, R.; Reyes, A.; Eychmüller, A.; Samano, E.; Seidel, R.; Erbe, A.

The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications. Based on this technique, the precise positioning of metallic and semiconducting nanoparticles along DNA nanostructures can be achieved. In this study, various DNA origami nanostructures (nanomolds, nanotubes and nanosheets) are used for the fabrication of nanoelectronic devices. To this end, gold nanoparticles, semiconductor quantum dots/rods are used in/on the DNA origami structures to create nanowires and transistor-like devices. The DNA origami nanowires and transistors were electrically characterized from room temperature (RT) down to 4.2K. Temperature-dependent characterizations of wires were performed in order to understand the dominant conduction mechanisms. Some nanowires showed pure metallic behavior.
Transistor like devices showed Coulomb blockade behavior at RT.
The study shows that self-assembled DNA structures can be used for nanoelectronic patterning and single electron devices.

Related publications

  • Lecture (Conference)
    DPG Spring Meeting, 31.03.-05.04.2019, Universität Regensburg, Germnay

Permalink: https://www.hzdr.de/publications/Publ-30411
Publ.-Id: 30411


Functionalized DNA Origami Nanostructures for Molecular Electronics

Bayrak, T.; Ye, J.; Weichelt, R.; Martinez-Reyes, A.; Samano, E.; Seidel, R.; Erbe, A.

The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications. Based on this technique, the precise positioning of metallic and semiconducting nanoparticles along DNA nanostructures can be achieved. In this study, various DNA origami nanostructures (nanomolds, nanotubes and nanosheets) are used for the fabrication of nanoelectronic devices. To this end, gold nanoparticles, semiconductor quantum dots/rods are used in/on the DNA origami structures to create nanowires and transistor-like devices. The DNA origami nanowires and transistors were electrically characterized from room temperature (RT) down to 4.2K. Temperature-dependent characterizations of wires were performed in order to understand the dominant conduction mechanisms. Some nanowires showed pure metallic behavior. Transistor like devices showed Coulomb blockade at RT. The study shows that self-assembled DNA structures can be used for nanoelectronic patterning and single electron devices.

Related publications

  • Lecture (Conference)
    IHRS NanoNET International Conferance, 08.-11.10.2019, Dresden, Germnay

Permalink: https://www.hzdr.de/publications/Publ-30410
Publ.-Id: 30410


Functionalized DNA Origami Nanostructures for Molecular Electronics

Bayrak, T.; Ye, J.; Weichelt, R.; Reyes, A.; Samano, E.; Seidel, R.; Erbe, A.

The DNA origami method provides a programmable bottom-up approach for creating nanostructures of any desired shape, which can be used as scaffolds for nanoelectronics and nanophotonics device fabrications. Based on this technique, the precise positioning of metallic and semiconducting nanoparticles along DNA nanostructures can be achieved. In this study, various DNA origami nanostructures (nanomolds and nanosheets) are used for the fabrication of nanoelectronic devices. To this end, gold nanoparticles, semiconductor quantum dots/rods are used in/on the DNA origami structures to create nanowires and transistor-like devices. The DNA origami nanowires and transistors were electrically characterized from room temperature (RT) down to 4.2K. Temperature-dependent characterizations of wires were performed in order to understand the dominant conduction mechanisms. Some nanowires showed pure metallic behavior. Transistor like devices showed Coulomb blockade behavior at RT. The study shows that self-assembled DNA structures can be used for nanoelectronic patterning and single electron devices.

Related publications

  • Open Access Logo Poster
    Nucleic Acid Nanotechnology: from algorithmic design to biochemical applications, 27.-29.05.2019, Aalto University, Finland

Permalink: https://www.hzdr.de/publications/Publ-30409
Publ.-Id: 30409


A Spectroscopic Study of the Interactions of Trivalent f-Elements with α-Chitin and its Constituents

Kammerlander, K.; Huittinen, N. M.; Kaden, P.; Stumpf, T.; Brunner, E.

A Spectroscopic Study of the Interactions of Trivalent f-Elements with α-Chitin and its Constituents

  • Lecture (Conference)
    GdCH Jahrestagung der Fachgruppe Nuklearchemie, 25.-27.09.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30408
Publ.-Id: 30408


Sorption of Trivalent f-Elements by Materials of Biological Origin: NMR and Luminescence Spectroscopic Studies

Kammerlander, K.; Köhler, L.; Huittinen, N. M.; Stumpf, T.; Brunner, E.

Sorption of Trivalent f-Elements by Materials of Biological Origin: NMR and Luminescence Spectroscopic Studies

  • Lecture (Conference)
    Migration 2019, 15.-20.09.2019, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-30407
Publ.-Id: 30407


Radiochemistry and the radioactive nuclear waste management

Mayordomo, N.

This invited lecture gives an overview to students of chemistry at Universidad de Alcalá (Spain) about radiochemistry and the ways to tackle radioactive waste

  • Invited lecture (Conferences)
    Lectures about chemistry (Lecciones de química), 06.02.2020, Alcalá de Henares, Spain

Permalink: https://www.hzdr.de/publications/Publ-30406
Publ.-Id: 30406


Commercial applications of research institute Tandem accelerators: the Rossendorf example

Akhmadaliev, S.

The Ion Beam Center (IBC) at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is a unique user facility with decades of experience applying ion beams for materials analysis and modification. The IBC provides ion beams of nearly all stable elements in an unique energy range from some tens of eV up to 60 MeV using tandem accelerators and electrostatic ion implanters, focused ion beam systems, a helium ion microscope, highly-charged ions systems, as well as an accelerator mass spectrometer (AMS) and a secondary ion spectrometer combined with a tandem accelerator. Annually, the IBC offers more than 16.000 hours of beam time for research and industrial purposes to users across the globe. Continuous access to the IBC is permitted via an online proposal procedure [1, 2]. In addition to the beam time, the IBC provides numerous add-on services including sample preparation, clean-room processing, surface and thin film metrology, optical and electron-beam lithography, thermal processing, thin-film deposition, optical and electrical characterization, electron microscopy and spectroscopy, X-ray investigations, as well as simulation of ion-related processes and data evaluation.
Since 2011, the spin-off HZDR Innovation GmbH [3] shares the IBC equipment and offers fast and direct access to the IBC for commercial services. The activity of the spin-off is focused on the high-energy ion implantation mostly for doping and defect engineering of semiconductors. Up to 8 inch wafers are handled (semi-)automatically at accelerators of IBC under clean room conditions. Many leading international microelectronic companies are customers of HZDR Innovation GmbH. HZDR Innovation GmbH provides an important contribution to the development and production of novel techniques for micro and power electronics, making semiconductor devices more effective and climate-friendly.

[1] http://www.hzdr.de/db/Cms?pNid=3249
[2] https://gate.hzdr.de/user/
[3] http://hzdr-innovation.de/2/

Related publications

  • Invited lecture (Conferences)
    NUSPRASEN Workshop on Nuclear Science Applications, 25.-27.11.2019, Helsinki, Finland

Permalink: https://www.hzdr.de/publications/Publ-30405
Publ.-Id: 30405


Structural and compositional modification of graphene oxide by means of medium and heavy ion implantation

Malinský, P.; Cutroneo, M.; Sofer, Z.; Szőkölová, K.; Böttger, R.; Akhmadaliev, S.; Macková, A.

Graphene and its allotropes belong to the new generation of materials. Due to their extraordinary electrical, mechanical and other properties, their application possibilities are vast. In this work, a study on interactions of graphene oxide (GO) layers using Au and Ga ions with energy of 40 keV was realized. Very shallow layers of GO are modified as low energy ions are depositing energy mostly in the upper layer due to the low projected ion ranges at most of 50 nm. The ion irradiation fluences of 5.0 × 1014 cm−2, 5.0 × 1015 cm−2 and 5.0 × 1016 cm−2 were used. Upon irradiation, the modified GO foils were characterised using nuclear analytical methods – Rutherford Backscattering Spectrometry (RBS), Elastic Recoil Detection Analysis (ERDA) and various conventional analytical methods such as Raman spectroscopy, Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-ray Photoelectron Spectroscopy (XPS), and 2-point conductivity measurements. Oxygen species removal was evidenced as the increasing function of the ion implantation fluence and oxygen depth profiles exhibited complex behaviour connected to implanted ion specie. The deep oxygen depletion in the broad surface layer accompanied by Ga diffusion into the depth was observed in Ga irradiated GO compared to Au irradiated samples which exhibited a narrow oxygen depleted layer at GO surface. XPS evidenced strong increase of C=C bonds compared to C-O bonds on the irradiated GO surface with increasing ion fluence, which was comparable for both ion species. Raman spectroscopy shows the modification of main phonon modes identified in GO. The D peak slight decrease and broadening was observed for GO irradiated with ion fluence above 5 × 1015 cm−2 and mainly for Au ion irradiation. FTIR analysis proved the oxygen containing functional group release with the increased ion fluence, mainly C-O group release after Au ion irradiation was observed. Simultaneously H-O stretching absorption peak is in FTIR spectrum reduced more significantly for Ga irradiated GO which is in accordance with RBS elemental analysis exhibiting the more pronounced hydrogen depletion. Electrical conductivity measurement shows the linear I-V characteristics for the GO irradiated using both ion species and all ion fluences; the surface layer exhibited conductive behaviour comparing to pristine GO non-linear I-V characteristics.

Keywords: Chemical properties; Electrical properties; Graphene oxide; Ion Irradiation

Related publications

Permalink: https://www.hzdr.de/publications/Publ-30404
Publ.-Id: 30404


The distribution bias of direct sampling with continues variables

van den Boogaart, K. G.; Selia, S. R. R.; Tolosana Delgado, R.

In direct sampling for the conditional simulation of random fields with continues distributions the probablity of finding exact matches of the local conditions in the training image is zero. We thus need to take samples with similar but different patterns. The maximum permissible difference is an algorithmic threshold parameter t controlling the speed, the reliability and the correctness of the simulation.

The contribution describes the effect that simulations sampled with this algorithm follow a conditional distribution, which is systematically biased with respect to the conditional distribution represented by the training images. This sampling bias is create by the fact that it is more likely to find conditioning events deviating from the observed conditioning shifted in the direction of the gradient of the marginal density of the conditioning events. These conditioning events however also typically have a conditional distribution shifted accordingly. The implicitly generated distribution of the conditional simulation is thus just not only (as it was always understood) a little smoothness with respect to the true distribution, but systematically biased. This sampling bias can be easily demostrated in simple Gaussian examples, where it introduces a regression to the mean type effect into a conditional simulation. The effect of the bias accumulates along the simulation path. The size of the sampling bias depends on the choosen tolerance, the choosen neighbourhood, the choosen iteration limit, and the local conditioning events.

The contribution will also discuss strategies to limit and control the effect of this sampling bias, by selecting appropriate algorithmic parameters, and by quantifying the DS sampling bias.

Keywords: Multipoint Geostatistics; Direct Sampling

  • Lecture (Conference)
    Geostats 2020, 17.-21.08.2020, Toronto, Canada

Permalink: https://www.hzdr.de/publications/Publ-30403
Publ.-Id: 30403


Unidirectional tilt of domain walls in equilibrium in biaxial stripes with Dzyaloshinskii–Moriya interaction

Pylypovskyi, O.; Kravchuk, V. P.; Volkov, O.; Faßbender, J.; Sheka, D.; Makarov, D.

The orientation of a chiral magnetic domain wall in a racetrack determines its dynamical properties. In equilibrium, magnetic domain walls are expected to be oriented perpendicular to the stripe axis. We demonstrate the appearance of a unidirectional domain wall tilt in out-of-plane magnetized stripes with biaxial anisotropy and Dzyaloshinskii--Moriya interaction (DMI). The tilt is a result of the interplay between the in-plane easy-axis anisotropy and DMI. We show that the additional anisotropy and DMI prefer different domain wall structure: anisotropy links the magnetization azimuthal angle inside the domain wall with the anisotropy direction in contrast to DMI, which prefers the magnetization perpendicular to the domain wall plane. Their balance with the energy gain due to domain wall extension defines the equilibrium magnetization the domain wall tilting. We demonstrate that the Walker field and the corresponding Walker velocity of the domain wall can be enhanced in the system supporting tilted walls.

Keywords: magnetism; doman wall; anisotropy; Dzyaloshinskii-Moriya interaction; Walker field; Walker velocity

Permalink: https://www.hzdr.de/publications/Publ-30401
Publ.-Id: 30401


Materials science for information technology

Helm, M.

Research at the Institute of Ion Beam Physics and Materials Research

Keywords: ion implanation; materials science; information technology

Related publications

  • Lecture (others)
    talk at UESTC, 15.10.2019, Chengdu, China

Permalink: https://www.hzdr.de/publications/Publ-30400
Publ.-Id: 30400


Tunable plasmonics in heavily doped GaAs via ion implantation and sub-second annealing

Duan, J.; Wang, M.; Helm, M.; Skorupa, W.; Zhou, S.; Prucnal, S.

Semiconductors with ultra-high doping level are attractive for the near- and mid-infrared plasmonics. The III-V compound semiconductors are characterized by high electron mobility and low effective mass, where the plasma edge can be tuned by tailoring the doping level. In this work, we present the formation of heavily doped p- and n-type GaAs utilizing ion implantation of Te, S and Zn, followed by sub-second annealing. We demonstrate that either the millisecond range flash lamp annealing (solid phase epitaxy) or nanosecond range pulsed laser annealing (liquid phase epitaxy) is able to recrystallized the implanted layers and electrically activate the dopants.The carrier concentration in the heavily doped p- and n-type GaAs with sub-second annealing treatment is in the range of 1019~1020 cm-3. The plasmonic properties of implanted and annealed GaAs samples were investigated by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The obtained ultra-highly GaAs films display a room-temperature plasma frequency above 2200 cm-1, which enables to exploit the plasmonic properties of GaAs for sensing in the mid-infrared spectral range.

Keywords: heavily doped GaAs; plasmonic; sub-second annealing

Related publications

  • Lecture (Conference)
    2019 DPG, 31.03.-05.04.2019, Regensbrug, Germany

Permalink: https://www.hzdr.de/publications/Publ-30399
Publ.-Id: 30399


Tunable plasmonics in heavily doped GaAs fabricated by ion implantation and sub-second annealing

Juanmei, D.; Helm, M.; Skorupa, W.; Zhou, S.; Prucnal, S.

Semiconductors with ultra-high doping level are attractive for the near- and mid-infrared plasmonics. The III-V compound semiconductors are characterized by high electron mobility and low electron effective mass, where the plasma edge can be tuned by tailoring the doping level. In this work, we present the formation of heavily doped p- and n-type GaAs utilizing ion implantation of Te, S and Zn, followed by sub-second annealing. We demonstrate that both the millisecond range flash lamp annealing (solid phase epitaxy) and nanosecond range pulsed laser annealing (liquid phase epitaxy) are able to recrystallize the implanted layers and electrically activate dopants. The carrier concentration in the heavily doped p- and n-type GaAs is in the range of 1019~1020 cm-3. The plasmonic properties of implanted and annealed GaAs samples were investigated by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The obtained GaAs films display a room-temperature plasma frequency above 2200 cm-1, which makes GaAs attractive for sensing in the mid-infrared spectral range.

Keywords: Heavily doped GaAs; mid-infrared plasmonic; sub-second annealing

Related publications

  • Poster
    2019 Spring Meeting of the European Materials Research Society, 16.-19.09.2019, Warsaw, Poland

Permalink: https://www.hzdr.de/publications/Publ-30398
Publ.-Id: 30398


Experimental and Theoretical Studies of Exchange-driven Chiral Effects

Volkov, O.

Broken magnetic symmetry is a key aspect in condensed matter physics and in particular in magnetism. It results in the appearance of chiral effects, e.g. topological Hall effect [1] and non-collinear magnetic textures including chiral domain walls and skyrmions [2,3]. These chiral structures are in the heart of novel concepts for magnonics [4], antiferromagnetic spintronics [5], spin-orbitronics [6] and oxitronics [7].
The main origin of the chiral symmetry breaking and thus for the magnetochiral effects in magnetic materials is associated to an antisymmetric exchange interaction, the intrinsic Dzaloshinskii-Moriya interaction (DMI). At present, tailoring of DMI is done rather conventionally by optimizing materials, either doping a bulk single crystal or adjusting interface properties of thin films and multilayers.
A viable alternative to the conventional material screening approach can be the exploration of the interplay between geometry and topology. This interplay is of fundamental interest throughout many disciplines in condensed matter physics, including thin layers of superconductors [8] and superfluids [9], nematic liquid crystals [10], cell membranes [11], semiconductors [12]. In the emergent field of curvilinear magnetism chiral effects are associated to the geometrically broken inversion symmetries [13]. Those appear in curvilinear architectures of even conventional materials. There are numerous exciting theoretical predictions of exchange- and magnetostatically-driven curvature effects, which do not rely on any specific modification of the intrinsic magnetic properties, but allow to create non-collinear magnetic textures in a controlled manner by tailoring local curvatures and shapes [14,15]. Until now the predicted chiral effects due to curvatures remained a neat theoretical abstraction.
Here, I review the very first experimental confirmation of the existence of the curvature-induced chiral interaction with exchange origin in a conventional soft ferromagnetic material. It is experimentally explored the theoretical predictions, that the magnetisation reversal of flat parabolic stripes shows a two step process. At the first switching event, a domain wall pinned by the curvature induced exchange-driven DMI is expelled leading to a magnetisation state homogeneous along the parabola's long axis. Measuring the depinning field enables to quantify the effective exchange-driven DMI interaction constant. The magnitude of the effect can be tuned by the parabola's curvature. It is found that the strength of the exchange-induced DMI interaction for the experimentally realised geometries is remarkably strong, namely $\approx 0.4~$mJ/m$^2$, compared the surface induced DMI. The presented study legitimates the predictive power of full-scale micromagnetic simulations to design the properties of ferromagnets through their geometry, thus stabilising chiral textures.

[1] N. Nagaosa, et al., Nature Nanotech. 8, 899 (2013)
[2] U. K. Rößler, et al., Nature 442, 797 (2006)
[3] A. Fert, et al., Nature Rev. Mat. 2, 17031 (2017)
[4] A. V. Chumak, et al., Nature Physics 11, 453 (2015)
[5] T. Jungwirth, et al., Nature Nanotech. 11, 231 (2016)
[6] I. M. Miron, et al., Nature 476, 189 (2011)
[7] V. Garcia, et al., Nature 460, 81 (2009)
[8] J. Tempere, et al., Phys. Rev. B 79, 134516 (2009)
[9] H. Kuratsuji, Phys. Rev. E 85, 031150 (2012)
[10] T. Lopez-Leon, et al., Nature Physics 7, 391 (2011)
[11] H. T. McMahon, et al., Nature 438, 590 (2005)
[12] C. Ortix, Phys. Rev. B 91, 245412 (2015)
[13] Y. Gaididei, et al., Phys. Rev. Lett. 112, 257203 (2014)
[14] J. A. Otálora, et al., Phys. Rev. Lett. 117, 227203 (2016)
[15] V. P. Kravchuk, et al., Phys. Rev. Lett. 120, 067201 (2018)

Keywords: Micromagnetism; curvilinear effects

  • Invited lecture (Conferences)
    Seminar at the Advanced Materials and Microsystems Laboratory, 05.12.2019, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-30397
Publ.-Id: 30397


Concept of artificial magnetoelectric materials via geometrically controlling curvilinear helimagnets

Volkov, O.; Rößler, U.; Faßbender, J.; Makarov, D.

Magnetoelectric materials are of the great interest due to their unique coupling of the magnetic and electrical order parameters. In these materials magnetic states can be manipulated via electric field and vice versa, offering exciting prospectives for energy efficient memory, logic and sensor devices. However, a sizeable magnetoelectric coupling for technologically relevant applications is obtained for a limited set of single-phase bulk materials. Typically, this restriction can be removed by using two-phase materials, containing strain-coupled magnetoelectric heterostructures based on piezoelectric-magnetostrictive bilayers. Although the concept is promising, there is a clear limitation regarding the fact that strain-induced changes result in the modification of all intrinsic magnetic parameters, in particular anisotropic couplings. Ideally, it would be advantageous that electric field control of magnetic state is achieved without change of global intrinsic magnetic parameters.

We propose a novel type of artificial magnetoelectric material [1], which allows an electric field-induced deterministic switching between magnetic states without influencing intrinsic magnetic parameters. The proposal refers to geometrically curved helimagnets [2,3] embedded in a piezoelectric matrix or sandwiched between two piezoelectric layers. In contrast to typical strain-coupled magnetoelectric heterostructures, we exploit the geometric coupling between the piezoelectric matrix and curvilinear helimagents. Namely, a small geometrical deformation causes a drastic modification of magnetic state of the helimagnet through a magnetic phase transition between a homogeneous magnetic state and a periodical one. Resulting transformations of the average magnetization from non-zero to zero value can be uniquely assigned to logical “1” and “0”. This paves the way towards the realization of novel magnetoelectric devices with geometrically tunable and deterministically switchable magnetic states.

We provide not only the general concept but also show analytical validation for a prototypical example of torsional nanospring helimagnets. Furthermore, we put forth a discussion on the feasibility of the experimental realization of the concept including the choice of materials and fabrication approaches.

[1] O. M. Volkov et al., J. Phys. D: Appl. Phys. (2019). doi:10.1088/1361-6463/ab2368.
[2] O. M. Volkov et al., Scientific Reports 8, 866 (2018).
[3] R. Streubel et al., J. Phys. D: Appl. Phys. (Topical Review) 49, 363001 (2016).

Keywords: Micromagnetism; curvilinear effects; magnetoelectric materials

  • Lecture (Conference)
    2019 MRS Fall meeting & Exhibit, 01.-06.12.2019, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-30396
Publ.-Id: 30396


Concept of artificial magnetoelectric materials via geometrically controlling curvilinear helimagnets

Volkov, O.; Rößler, U.; Faßbender, J.; Makarov, D.

Magnetoelectric materials are of the great interest due to their unique coupling of the magnetic and electrical order parameters, offering exciting prospectives for energy efficient memory, logic and sensor devices. However, a sizeable magnetoelectric coupling for technologically relevant applications is obtained for a limited set of single-phase bulk materials. Typically, this restriction can be removed by using two-phase materials, containing strain-coupled magnetoelectric heterostructures based on piezoelectric-magnetostrictive bilayers. Although the concept is promising, there is a clear limitation regarding the fact that strain-induced changes result in the modification of all intrinsic magnetic parameters, in particular anisotropic couplings. Ideally, it would be advantageous that electric field control of magnetic state is achieved without change of global intrinsic magnetic parameters.

We propose a novel type of artificial magnetoelectric material [1], which allows an electric field-induced deterministic switching between magnetic states without influencing intrinsic magnetic parameters. The proposal refers to geometrically curved helimagnets [2,3] embedded in a piezoelectric matrix or sandwiched between two piezoelectric layers. In contrast to typical strain-coupled magnetoelectric heterostructures, we exploit the geometric coupling between the piezoelectric matrix and curvilinear helimagents. Namely, a small geometrical deformation causes a drastic modification of magnetic state of the helimagnet through a magnetic phase transition between a homogeneous magnetic state and a periodical one. Resulting transformations of the average magnetization from non-zero to zero value can be uniquely assigned to logical “1” and “0”. This paves the way towards the realization of novel magnetoelectric devices with geometrically tunable and deterministically switchable magnetic states.

We provide not only the general concept but also show analytical validation for a prototypical example of torsional nanospring helimagnets. Furthermore, we put forth a discussion on the feasibility of the experimental realization of the concept including the choice of materials and fabrication approaches.

[1] O. M. Volkov et al., J. Phys. D: Appl. Phys. (2019). doi:10.1088/1361-6463/ab2368.
[2] O. M. Volkov et al., Scientific Reports 8, 866 (2018).
[3] R. Streubel et al., J. Phys. D: Appl. Phys. (Topical Review) 49, 363001 (2016).

Keywords: Micromagnetism; curvilinear effects; magnetoelectric materials

  • Lecture (Conference)
    2019 Conference on Magnetism and Magnetic Materials (MMM), 04.-08.11.2019, Las Vegas, USA

Permalink: https://www.hzdr.de/publications/Publ-30395
Publ.-Id: 30395


Theoretical and Experimental Study of Curvature Effects in Nanomagnetism

Volkov, O.

Broken magnetic symmetry is a key aspect in condensed matter physics and in particular in magnetism. It results in the appearance of chiral effects, e.g. topological Hall effect [1] and non-collinear magnetic textures including chiral domain walls and skyrmions [2,3]. These chiral structures are in the heart of novel concepts for magnonics [4], antiferromagnetic spintronics [5], spin-orbitronics [6] and oxitronics [7].
The main origin of the chiral symmetry breaking and thus for the magnetochiral effects in magnetic materials is associated to an antisymmetric exchange interaction, the intrinsic Dzaloshinskii-Moriya interaction (DMI). At present, tailoring of DMI is done rather conventionally by optimizing materials, either doping a bulk single crystal or adjusting interface properties of thin films and multilayers.
A viable alternative to the conventional material screening approach can be the exploration of the interplay between geometry and topology. This interplay is of fundamental interest throughout many disciplines in condensed matter physics, including thin layers of superconductors [8] and superfluids [9], nematic liquid crystals [10], cell membranes [11], semiconductors [12]. In the emergent field of curvilinear magnetism chiral effects are associated to the geometrically broken inversion symmetries [13]. Those appear in curvilinear architectures of even conventional materials. There are numerous exciting theoretical predictions of exchange- and magnetostatically-driven curvature effects, which do not rely on any specific modification of the intrinsic magnetic properties, but allow to create non-collinear magnetic textures in a controlled manner by tailoring local curvatures and shapes [14,15]. Until now the predicted chiral effects due to curvatures remained a neat theoretical abstraction.

[1] N. Nagaosa, et al., Nature Nanotech. 8, 899 (2013)
[2] U. K. Rößler, et al., Nature 442, 797 (2006)
[3] A. Fert, et al., Nature Rev. Mat. 2, 17031 (2017)
[4] A. V. Chumak, et al., Nature Physics 11, 453 (2015)
[5] T. Jungwirth, et al., Nature Nanotech. 11, 231 (2016)
[6] I. M. Miron, et al., Nature 476, 189 (2011)
[7] V. Garcia, et al., Nature 460, 81 (2009)
[8] J. Tempere, et al., Phys. Rev. B 79, 134516 (2009)
[9] H. Kuratsuji, Phys. Rev. E 85, 031150 (2012)
[10] T. Lopez-Leon, et al., Nature Physics 7, 391 (2011)
[11] H. T. McMahon, et al., Nature 438, 590 (2005)
[12] C. Ortix, Phys. Rev. B 91, 245412 (2015)
[13] Y. Gaididei, et al., Phys. Rev. Lett. 112, 257203 (2014)
[14] J. A. Otálora, et al., Phys. Rev. Lett. 117, 227203 (2016)
[15] V. P. Kravchuk, et al., Phys. Rev. Lett. 120, 067201 (2018)

Keywords: Micromagnetism; curvilinear effects

Related publications

  • Invited lecture (Conferences)
    Advanced Training Course “Spintronics Radar Detectors”, 14.-18.10.2019, Athens, Greece

Permalink: https://www.hzdr.de/publications/Publ-30394
Publ.-Id: 30394


Experimental observation of exchange-driven chiral effects in parabolic nanostripes

Volkov, O.

Broken magnetic symmetry is a key aspect in condensed matter physics and in particular in magnetism. It results in the appearance of chiral effects, e.g. topological Hall effect [1] and non-collinear magnetic textures including chiral domain walls and skyrmions [2,3]. These chiral structures are in the heart of novel concepts for magnonics [4], antiferromagnetic spintronics [5], spin-orbitronics [6] and oxitronics [7].
The main origin of the chiral symmetry breaking and thus for the magnetochiral effects in magnetic materials is associated to an antisymmetric exchange interaction, the intrinsic Dzaloshinskii-Moriya interaction (DMI). At present, tailoring of DMI is done rather conventionally by optimizing materials, either doping a bulk single crystal or adjusting interface properties of thin films and multilayers.
A viable alternative to the conventional material screening approach can be the exploration of the interplay between geometry and topology. This interplay is of fundamental interest throughout many disciplines in condensed matter physics, including thin layers of superconductors [8] and superfluids [9], nematic liquid crystals [10], cell membranes [11], semiconductors [12]. In the emergent field of curvilinear magnetism chiral effects are associated to the geometrically broken inversion symmetries [13]. Those appear in curvilinear architectures of even conventional materials. There are numerous exciting theoretical predictions of exchange- and magnetostatically-driven curvature effects, which do not rely on any specific modification of the intrinsic magnetic properties, but allow to create non-collinear magnetic textures in a controlled manner by tailoring local curvatures and shapes [14,15]. Until now the predicted chiral effects due to curvatures remained a neat theoretical abstraction.
Here, I review the very first experimental confirmation of the existence of the curvature-induced chiral interaction with exchange origin in a conventional soft ferromagnetic material. It is experimentally explored the theoretical predictions, that the magnetisation reversal of flat parabolic stripes shows a two step process. At the first switching event, a domain wall pinned by the curvature induced exchange-driven DMI is expelled leading to a magnetisation state homogeneous along the parabola's long axis. Measuring the depinning field enables to quantify the effective exchange-driven DMI interaction constant. The magnitude of the effect can be tuned by the parabola's curvature. It is found that the strength of the exchange-induced DMI interaction for the experimentally realised geometries is remarkably strong, namely $\approx 0.4~$mJ/m$^2$, compared the surface induced DMI. The presented study legitimates the predictive power of full-scale micromagnetic simulations to design the properties of ferromagnets through their geometry, thus stabilising chiral textures.

[1] N. Nagaosa, et al., Nature Nanotech. 8, 899 (2013)
[2] U. K. Rößler, et al., Nature 442, 797 (2006)
[3] A. Fert, et al., Nature Rev. Mat. 2, 17031 (2017)
[4] A. V. Chumak, et al., Nature Physics 11, 453 (2015)
[5] T. Jungwirth, et al., Nature Nanotech. 11, 231 (2016)
[6] I. M. Miron, et al., Nature 476, 189 (2011)
[7] V. Garcia, et al., Nature 460, 81 (2009)
[8] J. Tempere, et al., Phys. Rev. B 79, 134516 (2009)
[9] H. Kuratsuji, Phys. Rev. E 85, 031150 (2012)
[10] T. Lopez-Leon, et al., Nature Physics 7, 391 (2011)
[11] H. T. McMahon, et al., Nature 438, 590 (2005)
[12] C. Ortix, Phys. Rev. B 91, 245412 (2015)
[13] Y. Gaididei, et al., Phys. Rev. Lett. 112, 257203 (2014)
[14] J. A. Otálora, et al., Phys. Rev. Lett. 117, 227203 (2016)
[15] V. P. Kravchuk, et al., Phys. Rev. Lett. 120, 067201 (2018)

Keywords: Micromagnetism; curvilinear effects

Related publications

  • Invited lecture (Conferences)
    International Workshop “Curvilinear Magnetism”, 23.-24.05.2019, Kyiv, Ukraine

Permalink: https://www.hzdr.de/publications/Publ-30393
Publ.-Id: 30393


Mesoscale Dzyaloshinskii-Moriya interaction: geometrical tailoring of the magnetochiralit

Volkov, O.; Sheka, D.; Gaididei, Y.; Kravchuk, V.; Rößler, U.; Faßbender, J.; Makarov, D.

Magnetic crystals with broken chiral symmetry possess intrinsic spinorbit driven Dzyaloshinskii-Moriya interaction (DMI). Geometrically broken symmetry in curvilinear magnetic systems also leads to the appearance of extrinsic to the crystal exchange driven effective DMI [1,2]. The interplay between the intrinsic and geometrical-induced DMI paves the way to a mesoscale DMI, whose symmetry and strength depend on the geometrical and material parameters [3]. We demonstrate this approach on the example of a helix with intrinsic DMI. Adjusting the helical geometry allows to create new artificial chiral nanostructures with defined properties from standard magnetic materials. For instance, we propose a novel approach towards artificial magnetoelectric materials, whose state is controlled by means of the geometry.
[1] Y. Gaididei et. al, Phys. Rev. Lett. 112, 257203 (2014).
[2] R. Streubel et. al, J. Phys. D: Applied Physics 49, 363001 (2016).
[3] O. Volkov et. al, Scientific Reports 8, 866 (2018).

Keywords: Micromagnetism; curvilinear effects

  • Open Access Logo Lecture (Conference)
    DPG Spring Meeting, Regensburg 2019, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30392
Publ.-Id: 30392


High-motility visible light-driven Ag/AgCl Janus microswimmers interacting with passive beads

Wang, X.; Baraban, L.; Misko, V. R.; Nori, F.; Formanek, P.; Huang, T.; Cuniberti, G.; Faßbender, J.; Makarov, D.

Visible light driven nano/micro swimmers are promising candidates for potential biomedical and environmental applications. However, the previously reported mean squared displacement (MSD) values are low, typically in the range of up to 200 µm2 (when measured over 10 s), even under the favourable UV light illumination.[1,2] This is a severe drawback for the applications where the efficient transport of micromotors within a vessel is demanded.

Here, we demonstrate Ag/AgCl-based spherical Janus micromotors that reveal an efficient propulsion under visible blue light illumination.[3] The proper design of an Ag/AgCl-based micromotor can boost the MSD to a remarkable value of 3000 µm2 (over 10 s) in pure H2O, even when activated with blue light (excitation λ = 450-490 nm). The revealed propulsion of micromotors owns a dependence of the intensity of visible light, which is contributed by the couple plasmonic light absorption of Ag/AgCl and the efficient photochemical decomposition of AgCl. With the motion comparisons of individual Janus particle, small cluster, and large cluster, the effect of suppressed rotational diffusion has been revealed experimentally and in numerical simulations. Furthermore, we show that Ag/AgCl-based Janus micromotors reveal efficient exclusion effect to their surrounding passive polystyrene (PS) beads in pure H2O.[4] The exclusion efficiency is controlled by the number of single Janus PS/Ag/AgCl particles that compose a cluster. Using numerical simulations of the Langevin equations, we gain a fundamental understanding not only the diffusion constants, but also the system-specific interaction parameter between Janus motors and passive beads.

1. Ibele, M., et al., Angew. Chem. Int. Ed. 2009, 48, 3308.
2. Simmchen, J., et al., ChemNanoMat 2017, 3, 65.
3. Wang, X., et al., Small 2018, 14, 1803613.
4. Wang, X., et al., Small 2018, 14, 1802537.

Keywords: Active Janus particles; exclusion interaction; passive beads; visible light‐driven micromotors

Related publications

  • Lecture (Conference)
    Materials Research Society Fall Meeting, 01.-06.12.2019, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-30391
Publ.-Id: 30391


Experimental confirmation of exchange-driven DMI

Volkov, O.; Kakay, A.; Kronast, F.; Mönch, J. I.; Mawass, M.-A.; Faßbender, J.; Makarov, D.

Dzyaloshinskii-Moriya interaction (DMI) is a key ingredient which allows to obtain chiral non-collinear magnetic textures, e.g. chiral domain walls and skyrmions. The conventional spin-orbit induced DMI emerges in gyrotropic crystals or at the interfaces. Therefore, tailoring of DMI is done by optimizing materials. A viable alternative to the material screening approach relies on the use of geometrically broken symmetries of conventional materials, where local geometrical curvatures generate effective exchange-induced DMI.
Here, we provide the very first experimental confirmation of the existence of the curvature-induced DMI in a Permalloy parabolic nanostripe. By analyzing the evolution of transversal domain wall (DW) [1] under the influence of external field we correlate the depinning field of the DW with the curvature-induced DMI field. We put forth a framework to analyze this field and assess the strength of the effective DMI.
[1] O. Volkov et. al, Physica Status Solidi – Rapid Research Letters, 1800309 (2018).

Keywords: Micromagnetism; curvilinear effects

Related publications

  • Lecture (Conference)
    DPG Spring Meeting, Regensburg 2019, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30390
Publ.-Id: 30390


Magnetically-triggered ultrafast soft robots with embedded magnetic cognition and feedback control

Wang, X.; Canon Bermudez, G. S.; Faßbender, J.; Makarov, D.

In the last years, soft robots have been designed and developed to fulfil demands of better malleability and adaptability to changing environment [1-2]. They can be made of various stimuli responsive materials, which respond to magnetic field [3], light [4], temperature [5], electric fields [6], chemicals [7], pressure [8], etc. In contrast to other actuation mechanisms, magnetic fields are appealing for numerous application scenarios (e.g. environmental, biological, medical), where their long-range penetration, easy accessibility, and controllability [2, 9, 10] offer exciting advantages. Despite the significant advances in soft magnetic actuators, real-time monitoring and precise feedback control [11-13] remain a challenge for magnetic soft robots.

Here, we present a soft robotic system capable of precisely controlling its deformation degree by means of embedded highly compliant, high-performance magnetic sensors. Our ultrathin (7-100 μm) and ultrafast soft robots that can be actuated by in external magnetic fields pulsating at rates of up to 200 Hz. The high-performance magnetic field sensor is based on the giant magnetoresistive effect and is prepared on ultrathin polymeric foils [14-17] to assure its high mechanical stability combined with mechanical imperceptibility. The latter is crucial to avoid any disturbance of the soft actuator due to the presence of magnetic sensing device. The self-sensing function is realized by monitoring the change of the sensor signal upon approaching it to a magnetic patch applied to the soft robot. This concept of an entirely soft and integrated sensor-actuator system enables contactless self-tracking of motion for magnetic soft robots and can be readily extended to other stimuli-driven soft actuators. These developments will pave the way towards intelligent soft robots, autonomous and reactive soft devices, and new types of human-robot interaction.

[1] D. Rus et al., Nature 521, 467 (2015)
[2] L. Hines et al., Adv. Mater. 29, 13 (2017)
[3] J. Y. Kim et al., Nat Mat. 10, 747 (2011)
[4] J. Deng et al., J. Am. Chem. Soc. 138, 225 (2016)
[5] Y. S. Kim et al., Nat Mat. 14, 1002 (2015)
[6] T. Mirfakhrai et al., Materials Today 10, 30 (2007)
[7] Q. Zhao et al., Nat Commun 5 (2014)
[8] SA. Morin et al., Science 337, 828 (2012)
[9] W. Hu et al., Nature 554, 81(2018)
[10] Kim. Y, et al., Nature 558, 274 (2018)
[11] T. G. Thuruthel et al., Sci Robot. 4, eaav1488 (2019)
[12] J. A. Lewis et al., Adv. Mater. 30, 1706383 (2018)
[13] W. Zhang et al., Adv Funct Mater. 29, 1806057 (2019)
[14] M. Melzer et al., Adv. Mater. 27, 1274 (2015)
[15] G. S. C. Bermúdez et al., Nat Electron. 1, 589 (2018)
[16] G. S. C. Bermúdez et al., Sci Adv., 4, eaao2623 (2018)
[17] P. N. Granell et al., npj Flexible Electronics, 3, 3 (2018)

Keywords: Soft robot; magnetic sensor; feedback control

Related publications

  • Lecture (Conference)
    Materials Research Society Fall Meeting, 01.-06.12.2019, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-30389
Publ.-Id: 30389


Experimental and theoretical study of curvature effects in parabolic nanostripes

Volkov, O.; Kronast, F.; Mönch, J. I.; Mawass, M.-A.; Kakay, A.; Faßbender, J.; Makarov, D.

Curvilinear magnetic objects are in the focus of intensive research due to the possibility to obtain new fundamental effects and stabilize topologically non-trivial magnetic textures at the nanoscale [1]. The physics in these systems is driven by the interplay between exchange and magnetostatic interactions, which contain spatial derivatives in their energy functionals. This makes both interactions sensitive to the appearance of bends and twists in the physical space.
Here, we address experimentally and theoretically curvature-induced effects in parabolic nanostripes with different geometrical parameters [2]. We show that two different magnetic states can appear: the homogeneous magnetic distribution along the parabolic stripe and a state with a transversal domain wall pinned at the vertex of the parabola. The analytical calculation, based on local magnetostatic model, showed its validity and applicability in a wide range of geometrical parameters.
[1] R. Streubel et al., J. Phys. D: Applied Physics 49, 363001 (2016).
[2] O. Volkov et al., Physica Status Solidi – Rapid Research Letters, 1800309 (2018).

Keywords: Micromagnetism; curvilinear effects

Related publications

  • Lecture (Conference)
    DPG Spring Meeting, Regensburg 2019, 31.03.-05.04.2019, Regensburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-30388
Publ.-Id: 30388


Magnetic and Magnetothermal Properties of Hydrogenated Materials Based on Rare Earths and Iron

Paukov, M. A.; Ivanov, L. A.; Gorbunov, D.; Tereshnina, I. S.

Iron-rich rare-earth compounds are the basis for high-energy permanent magnets. These include the R(Fe,T)12, R2Fe17, and R2FeB intermetallics (R = rare earth; T = Ti, V, Mo, Si) that readily absorb hydrogen, which changes their fundamental and functional characteristics. In this letter, we investigate the stability of the magnetic properties of some hydrides with maximum hydrogen content (namely, TmFe11TiH1 and Tm2Fe17H5.5) in a wide temperature range using high magnetic fields. The magnetic phase transition from the ferrimagnetic to the ferromagnetic state was studied immediately after hydrides were obtained, as well as after one year of storage of the samples at ambient temperature. Only the TmFe11TiH hydride is stable over time. The effect of hydrogen on the magnetothermal properties of the Nd2Fe14B and Nd1Pr1Fe14B compounds and a range of magnetic phase transitions were also investigated. Hydrogenation leads to a decrease in the magnetocaloric effect in all investigated compounds as a result of an increase in the distance between magnetically active ions due to the lattice expansion. A magnetic phase diagram is constructed.

Permalink: https://www.hzdr.de/publications/Publ-30387
Publ.-Id: 30387


Anisotropic field-induced ordering in the triangular-lattice quantum spin liquid NaYbSe2

Ranjith, K. M.; Luther, S.; Reimann, T.; Schmidt, B.; Schlender, P.; Sichelschmidt, J.; Yasuoka, H.; Strydom, A. M.; Scurschii, I.; Wosnitza, J.; Kühne, H.; Doert, T.; Baenitz, M.

High-quality single crystals of NaYbSe2, which resembles a perfect triangular-lattice antiferromagnet without intrinsic disorder, are investigated by magnetization and specific heat, as well as the local probe techniques nuclear magnetic resonance (NMR) and electron spin resonance. The low-field measurements confirm the absence of any spin freezing or long-range magnetic order down to 50 mK, which suggests a quantum spin liquid ground (QSL) state with gapless excitations. Instability of the QSL state is observed upon applying magnetic fields. For the H⊥c direction, a field-induced magnetic phase transition is observed above 2 T from the CP(T ) data, agreeing with a clear Ms/3 plateau of M(H), which is associated with an up-up-down spin arrangement. For the H ǀǀ c direction, a field-induced transition could be evidenced at a much higher field range (9–21 T). The 23Na NMR measurements provide microscopic evidence of field-induced ordering for both directions. A reentrant behavior of TN, originating from the thermal and quantum spin fluctuations, is observed for both directions. The anisotropic exchange interactions J ≃ 4.7 K and Jz ≃ 2.33 K are extracted from the modified bond-dependent XXZ model for the spin- 1/2 triangular-lattice antiferromagnet. The absence of magnetic long-range order at zero fields is assigned to the effect of strong bond frustration, arising from the complex spin-orbit entangled 4 f ground state. Finally, we derive the highly anisotropic magnetic phase diagram, which is discussed in comparison with the existing theoretical models for spin- 1/2 triangular-lattice antiferromagnets.

Permalink: https://www.hzdr.de/publications/Publ-30386
Publ.-Id: 30386


Microscopic insights into the disorder induced phase transition in FeRh thin films

Eggert, B.; Schmeink, A.; Potzger, K.; Lindner, J.; Fassbender, J.; Ollefs, K.; Keune, W.; Bali, R.; Wende, H.

By employing 57Fe conversion electron Mössbauer spectroscopy, we qualitatively determined the changes of the microscopic Fe moment of chemical disordered epitaxial B2-FeRh(001) thin films, where the chemical disorder has been induced by ion irradiation with Ne+. Apart from the initial magnetic splitting at 25.4 T an additional sextet contribution arises with an hyperfine field of 27.4 T. A comparison between the structural disorder and the temperature induced phase transition shows a similar change of the 57Fe hyperfine field as a function of the macroscopic magnetisation. This gives an indirect indication, that the metamagnetic phase transition proceeds via a defect-driven domain nucleation of ferromagnetic domains in the antiferromagnetic matrix, as it was suggested based on XPEEM and nano-XRD measurements along the phase transition [1]. We would like to thank the Ion Beam Center at Helmholtz-Zentrum Dresden-Rossendorf for providing the necessary facilities and acknowledge the financial support by DFG (WE2623/17-1).
D. Keavney et al. Scientific Reports 8 1778 (2018)

Related publications

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 31.03.-05.04.2019, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30385
Publ.-Id: 30385


Frustrated and low-dimensional magnetic materials in high magnetic fields

Wosnitza, J.

es liegt keine inhaltliche Kurzfassung des Vortrages vor

  • Invited lecture (Conferences)
    VII European-Asian Symposium “Trends in MAGnetism”, EASTMAG 2019,, 08.-13.09.2019, Ekaterinburg, Russland

Permalink: https://www.hzdr.de/publications/Publ-30384
Publ.-Id: 30384


Materials research in high magnetic fields

Wosnitza, J.

es liegt keine inhaltliche Kurzfassung des Vortrages vor

  • Invited lecture (Conferences)
    HFML-FELIX User Meeting, 08.-10.07.2019, Nijmegen, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-30383
Publ.-Id: 30383


Modulated Order Parameter in the FFLO State of Layered Organic Superconductors

Wosnitza, J.

es liegt keine inhaltliche Kurzfassung des Vortrages vor

  • Invited lecture (Conferences)
    Gordon Research Conference on Superconductivity, 12.-18.05.2019, Les Diablerets, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-30382
Publ.-Id: 30382


Microscopic evidence for the FFLO state in layered organic superconductors

Wosnitza, J.

es liegt keine inhaltliche Kurzangabe vor

  • Invited lecture (Conferences)
    3rd International Symposium of the SFB/TR 49 on “Novel states in correlated con-densed matter – from model systems to real materials”, 18.-20.03.2019, Bad Neuenahr, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30381
Publ.-Id: 30381


Tunable magnetic vortex dynamics in ion-implanted permalloy disks

Ramasubramanian, L.; Kákay, A.; Fowley, C.; Yildirim, O.; Matthes, P.; Sorokin, S.; Titova, A.; Hilliard, D.; Böttger, R.; Hübner, R.; Gemming, S.; Schulz, S. E.; Kronast, F.; Makarov, D.; Faßbender, J.; Deac, A. M.

Nanoscale, low-phase noise, tunable transmitter-receiver links are key for enabling the progress of wireless communi-cation. We demonstrate that vortex-based spin-torque nano-oscillators, which are intrinsically low-noise devices due to their topologically-protected magnetic structure, can achieve frequency tunability when submitted to local ion im-plantation. In the experiments presented here, the gyrotropic mode is excited with spin-polarized alternating currents and anisotropic magnetoresistance measurements yield discreet frequencies from a single device. Indeed, chromium-implanted regions of permalloy disks exhibit different saturation magnetisation than the surrounding, non-irradiated areas, and thus different resonance frequency, corresponding to the specific area where the core is gyrating. Our study proves that such devices can be fabricated without the need of further lithographical steps, suggesting ion irradiation can be a viable and cost-effective fabrication method for densely-packed networks of oscillators.

Keywords: electrical detection; vortex dynamics; frequency tunability; ion implantation; reduced saturation magnetisation

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Permalink: https://www.hzdr.de/publications/Publ-30380
Publ.-Id: 30380


Spin-transport in magnetic tunnel junctions with a zero-moment half-metallic electrode

Titova, A.; Fowley, C.; Lau, Y.-C.; Borisov, K.; Atcheson, G.; Stamenov, P.; Coey, M.; Rode, K.; Lindner, J.; Faßbender, J.; Deac, A. M.

The Big Data revolution has spurred the social need for transmitting ever-larger amounts of data and increasing data transmission speed. Mobile data speeds operating in the low GHz band will not be sufficient in the years to come, and society and researchers, therefore, look towards THz frequencies for next-generation wireless communication. To be successful, cheap and compact THz-transmitters/receivers have to be created. From the field of spintronics, spin-transfer-torque nano-oscillators (STNOs) may offer a solution for this demand, provided that their output frequency can be increased. In such devices, a spin-polarized current induces magnetization dynamics at frequencies of the same order of magnitude as their resonance frequencies. The operating frequencies for current STNOs based on typical transition metal-based ferromagnets and their derivatives lie in the GHz range, as a consequence of their low magnetic anisotropy and high magnetization. On the other hand, ferrimagnetic materials with ultra-high effective anisotropy fields are very promising, as they exhibit magnetic resonances of several hundred GHz, with antiferromagnetic modes in the THz. By integrating such materials into STNOs, sub-THz and even THz wireless emission may be achieved. In order to obtain high output power, the multilayer stacks have to exhibit high magnetoresistive effects: giant magnetoresistance (GMR) or tunneling magnetoresistance (TMR). High spin polarization is a necessary condition for strong magnetoresistive and spin-transfer effects. Therefore half-metals, which are metallic for one spin direction and semiconducting for the other, appear as the ideal choice. The focus of the work presented here is high anisotropy compensated ferrimagnetic half-metals (CFHMs) – a class of materials predicted in 1995 by van Leuken and de Groot. CFHMs behave like antiferromagnets (AFMs) with respect to external magnetic fields, since the magnetic moments of the two sublattices compensate, while simultaneously exhibiting half-metallic electron transport behavior. Many attempts had been made to fabricate such materials. Currently, MnGa-based alloys, where high anisotropy is coupled with low magnetization, attract intense attention and some have already been integrated into magnetic tunnel junctions (MTJs). Complete magnetic compensation in such alloys is, however, difficult to obtain. This was first realized in 2014 in Mn2RuxGa (MRG), which is a material that combines ideal properties like low magnetization, high magnetic anisotropy, and large spin polarization.

Here, the first demonstration of successful integration of MRG in the perpendicular magnetic tunnel junction stack is presented. The magnitude of TMR obtained in the stacks where the MgO barrier was used, although high, can still be improved. The main reason for TMR ratios being lower than what theory predicts is the presence of impurities in the tunnel barrier. In order to enhance the device's performance, different insertion layers between MgO and MRG were incorporated. These layers are diffusion barriers which stop Mn diffusion into the tunnel barrier. The highest TMR to-date (40 % at 10 K) was achieved in MgO-based stacks where a layer of Al 0.6 nm is incorporated. Within this thesis it was demonstrated that the TMR is insensitive to the compensation of the ferromagnetic MRG electrode, thereby, highlighting the fundamental difference between an antiferromagnet and a compensated half-metallic ferrimagnet. Furthermore, another tunnel barrier – Al2O3 (which is expected to be less sensitive to contamination than MgO) – has been integrated into MRG-based MTJ stacks. The current work provides a detailed study of the annealing, the bias voltage applied across the tunnel barrier and the external temperature influence on the performance of MRG-based MTJs. The stacks were analyzed not only via magnetotransport measurements, but also from the point of view of their structural and magnetic properties. This work contributes to the better understanding of spin transport in MRG-based MTJs and shows that these devices exhibit sufficient tunneling magnetoresistance ratios to observe current-induced magnetization dynamics, and, hence, establish a cornerstone of future spintronics devices.

Part of this work was carried out under the EU Project TRANSPIRE - DLV-737038.

Keywords: Magnetic tunnel junctions; Heusler compound; Ferrimagnet; Half-metal

Related publications

  • Invited lecture (Conferences)
    11th International Workshop on nanomagnetism and its novel applications SpinS-2019, 02.-04.10.2019, Duisburg/Mülheim an der Ruhr, Germany

Permalink: https://www.hzdr.de/publications/Publ-30379
Publ.-Id: 30379


Ion Irradiation Induced Cobalt/Cobalt Oxide Heterostructures: From Materials to Devices

Hilliard, D.; Yildirim, O.; Fowley, C.; Arekapudi, S. S. P. K.; Cansever, H.; Böttger, R.; Hlawacek, G.; Hellwig, O.; Lindner, J.; Faßbender, J.; Deac, A. M.

The demand on high data transfer and storage capacities requires smaller devices to transmit or save data. Forming well-defined ferromagnetic and electrically conducting volumes in a non-magnetic and insulating matrix in nanometer dimensions can pave a way to the production of such small devices. Oxygen reduction in Co3O4/Pd multilayers is possible by local proton irradiation resulting in ferromagnetic and conducting Co embedded in a nonmagnetic and insulating Co3O4 matrix [1].
To understand the mechanism behind this, we analysed in-plane single- and out-of-plane multilayer cobalt oxide films after H+ irradiation. We also confined irradiated areas on films in the range of microns to sub-micron to ascertain the lateral distribution of displaced oxygen, while establishing vertical Co/CoO interfaces which would lead to exchange bias across said interfaces.
Irradiated films were characterized by SQUID magnetometry to estimate the effective O removal. Figure 1 (a) shows hysteresis loops for single layers irradiated with various doses and (b) multilayer systems irradiated with a fixed dose. In (a) we see that irradiating single layer films results in minimal O removal by measuring the saturation magnetization Ms. Geometrical confinement of the irradiated region indeed increases the Ms suggesting lateral O displacement, although this value is still only about 10% of bulk Co metal ((a) inset). The effect is much more pronounced in 0.8 nm CoO multilayers as indicated by the presence of perpendicular magnetic anisotropy (b).
Figure 2 shows a loop shift for the multilayer (green) after field cooling demonstrating the formation of vertical Co/CoO interfaces post irradiation. This result is not seen in a single layer system (orange) as the layer is too thick to maintain a well-defined interface. These findings present new opportunities of device fabrication in single and bilayer systems.

Keywords: ion; irradiation; proton; cobalt oxide; CoO; Co3O4; paramagnetic; ferromagnetic; reduction; removal; oxygen; displacement; exchange; bias; magnetization; antiferromagnetic; perpencular; magnetic; anisotropy

Related publications

  • Lecture (Conference)
    2019 Joint MMM-Intermag Washington DC, 14.-18.01.2019, Washington DC, USA

Permalink: https://www.hzdr.de/publications/Publ-30378
Publ.-Id: 30378


Comparison of STED, confocal and optical microscopy of ultra-short pitch cholesterics

Pišljar, J.; Posnjak, G.; Pajk, S.; Godec, A.; Podlipec, R.; Kokot, B.; Muševič, I.

The goal of this work is to compare experimentally achievable resolution limits of three different optical microscopy techniques in chiral nematic liquid crystals: (i) standard optical polarisation microscopy, (ii) confocal optical microscopy using fluorescently labelled liquid crystal and (iii) Stimulated Emission Depletion (STED) microscopy using custom synthesised fluorescent dyes. The microscopy experiments on micrometre thin LC samples reveal that the lateral resolution better than ~90 nm can be achieved using STED technique in thin layers of liquid crystals. The standard optical microscopy with index matching between the objective and the sample cover glass in combination with short-wavelength narrow-band optical illumination is quite competitive to STED technique and optical details as small as ~150 nm could be resolved using aberration limited microscope.

Keywords: Sections; STED; optical microscopy; confocal microscopy; lateral resolution; short pitch cholesteric; fingerprint texture

Permalink: https://www.hzdr.de/publications/Publ-30376
Publ.-Id: 30376


Concept of artificial magnetoelectric materials via geometrically controlling curvilinear helimagnets

Volkov, O.; Rößler, U. K.; Faßbender, J.; Makarov, D.

A novel type of artificial magnetoelectric material, which allows an electric field-induced deterministic switching between magnetic states without influencing intrinsic magnetic parameters, is proposed. It refers to three dimensional curvilinear helimagnets, e.g. torsion springs, embedded in a piezoelectric matrix. In contrast to conventional strain-coupled magnetoelectric heterostructures based on piezoelectric-magnetostrictive bilayers, we exploit the geometrical coupling of the matrix to the curvilinear helimagnet with intrinsic chiral Dzyaloshinskii–Moriya interactions. Namely, the magnetic state is modified due to the change of geometrical parameters of the curved nanomagnet. Theoretically, the essence of the proposal is analysed for a deformable torsional spring made of helimagnetic material. In response to the geometrical change magnetic phase transition between the homogeneous and a periodically modulated state can be driven in a wide range of geometrical parameters. Resulting transformations of the average magnetization from non-zero to zero value can be uniquely assigned to logical ‘1’ and ‘0’. As the chiral magnetic properties are easier to control by mechanical distortion than effective anisotropies, our concept should lead to a robust design of novel magnetoelectric devices.

Keywords: Curvilinear magnetism; Helimagnet; Magnetoelectric material; Converse magnetoelectric effect

Permalink: https://www.hzdr.de/publications/Publ-30375
Publ.-Id: 30375


Gas-liquid two-phase flow in a centrifugal pump mock-up with swirling gas flow injection at 1600 rpm

Bieberle, A.; Schäfer, T.
Project Member: Bieberle, Martina; Project Member: Neumann-Kipping, Martin; DataCollector: Wolf, Jan; Project Leader: Hampel, Uwe

This data repository contains reconstructed and quantitatively analyzed gas-liquid two-phase distributions obtained from a centrifugal pump mock-up whose geometry is related to a commercially available industrial centrifugal pump. As measurement system the ultrafast electron beam X-ray CT scanner (UFXCT) is applied with a frame rate of 2,500 Hz, single-plane mode and a total scanning interval of 5 seconds. The data repository contains:

  • Reconstructed raw data sets (Algebraic Reconstruction Technique from the UFO framework) for different inlet gas fractions (eps0.0xx) at constant 1600 rpm and for both rotating and back-rotated impeller positions, respectively
  • Extracted RPM per CT scan (frame) including its raw data
  • Extracted angular positions of the impeller mock-up per frame
  • Calculated quantitative gas fraction data sets (static impeller position)
  • Time-averaged gas fraction distribution and its corresponding averaged variance
  • Pump and impeller mask data
  • Additional data obtained from the SPS server with a sampling frequency of 1 Hz

Keywords: centrifugal pump; gas-liquid two-phase flow; ultrafast electron beam X-ray computed tomography

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Permalink: https://www.hzdr.de/publications/Publ-30374
Publ.-Id: 30374


Gas-liquid two-phase flow in a centrifugal pump mock-up with swirling gas flow injection at 1480 rpm

Bieberle, A.; Schäfer, T.
Project Member: Bieberle, Martina; Project Member: Neumann-Kipping, Martin; DataCollector: Wolf, Jan; Project Leader: Hampel, Uwe

This data repository contains reconstructed and quantitatively analyzed gas-liquid two-phase distributions obtained from a centrifugal pump mock-up whose geometry is related to a commercially available industrial centrifugal pump. As measurement system the ultrafast electron beam X-ray CT scanner (UFXCT) is applied with a frame rate of 2,500 Hz, single-plane mode and a total scanning interval of 10 seconds. The data repository contains:

  • Reconstructed raw data sets (Algebraic Reconstruction Technique from the UFO framework) for different inlet gas fractions (eps0.0xx) at constant 1480 rpm and for both rotating and back-rotated impeller positions, respectively
  • Extracted RPM per CT scan (frame) including its raw data
  • Extracted angular positions of the impeller mock-up per frame
  • Calculated quantitative gas fraction data sets (static impeller position)
  • Time-averaged gas fraction distribution and its corresponding averaged variance
  • Pump and impeller mask data
  • Additional data obtained from the SPS server with a sampling frequency of 1 Hz

Keywords: centrifugal pump; gas-liquid two-phase flow; ultrafast electron beam X-ray computed tomography

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Permalink: https://www.hzdr.de/publications/Publ-30373
Publ.-Id: 30373


Gas-liquid two-phase flow in a centrifugal pump mock-up with swirling gas flow injection at 1300 rpm

Bieberle, A.; Schäfer, T.
Project Member: Bieberle, Martina; Project Member: Neumann-Kipping, Martin; DataCollector: Wolf, Jan; Project Leader: Hampel, Uwe

This data repository contains reconstructed and quantitatively analyzed gas-liquid two-phase distributions obtained from a centrifugal pump mock-up whose geometry is related to a commercially available industrial centrifugal pump. As measurement system the ultrafast electron beam X-ray CT scanner (UFXCT) is applied with a frame rate of 2,500 Hz, single-plane mode and a total scanning interval of 5 seconds. The data repository contains:

  • Reconstructed raw data sets (Algebraic Reconstruction Technique from the UFO framework) for different inlet gas fractions (eps0.0xx) at constant 1300 rpm and for both rotating and back-rotated impeller positions, respectively
  • Extracted RPM per CT scan (frame) including its raw data
  • Extracted angular positions of the impeller mock-up per frame
  • Calculated quantitative gas fraction data sets (static impeller position)
  • Time-averaged gas fraction distribution and its corresponding averaged variance
  • Pump and impeller mask data
  • Additional data obtained from the SPS server with a sampling frequency of 1 Hz

Keywords: centrifugal pump; gas-liquid two-phase flow; ultrafast electron beam X-ray computed tomography

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Permalink: https://www.hzdr.de/publications/Publ-30372
Publ.-Id: 30372


Gas-liquid two-phase flow in a centrifugal pump mock-up with disperse gas flow injection at 1600 rpm

Bieberle, A.; Schäfer, T.
Project Member: Bieberle, Martina; Project Member: Neumann-Kipping, Martin; DataCollector: Wolf, Jan; Project Leader: Hampel, Uwe

This data repository contains reconstructed and quantitatively analyzed gas-liquid two-phase distributions obtained from a centrifugal pump mock-up whose geometry is related to a commercially available industrial centrifugal pump. As measurement system the ultrafast electron beam X-ray CT scanner (UFXCT) is applied with a frame rate of 2,500 Hz, single-plane mode and a total scanning interval of 5 seconds. The data repository contains:

  • Reconstructed raw data sets (Algebraic Reconstruction Technique from the UFO framework) for different inlet gas fractions (eps0.0xx) at constant 1600 rpm and for both rotating and back-rotated impeller positions, respectively
  • Extracted RPM per CT scan (frame) including its raw data
  • Extracted angular positions of the impeller mock-up per frame
  • Calculated quantitative gas fraction data sets (static impeller position)
  • Time-averaged gas fraction distribution and its corresponding averaged variance
  • Pump and impeller mask data
  • Additional data obtained from the SPS server with a sampling frequency of 1 Hz

Keywords: centrifugal pump; gas-liquid two-phase flow; ultrafast electron beam X-ray computed tomography

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Permalink: https://www.hzdr.de/publications/Publ-30371
Publ.-Id: 30371


Gas-liquid two-phase flow in a centrifugal pump mock-up with disperse gas flow injection at 1480 rpm

Bieberle, A.; Schäfer, T.
Project Member: Bieberle, Martina; Project Member: Neumann-Kipping, Martin; DataCollector: Wolf, Jan; Project Leader: Hampel, Uwe

This data repository contains reconstructed and quantitatively analyzed gas-liquid two-phase distributions obtained from a centrifugal pump mock-up whose geometry is related to a commercially available industrial centrifugal pump. As measurement system the ultrafast electron beam X-ray CT scanner (UFXCT) is applied with a frame rate of 2,500 Hz, single-plane mode and a total scanning interval of 5 seconds. The data repository contains:

  • Reconstructed raw data sets (Algebraic Reconstruction Technique from the UFO framework) for different inlet gas fractions (eps0.0xx) at constant 1480 rpm and for both rotating and back-rotated impeller positions, respectively
  • Extracted RPM per CT scan (frame) including its raw data
  • Extracted angular positions of the impeller mock-up per frame
  • Calculated quantitative gas fraction data sets (static impeller position)
  • Time-averaged gas fraction distribution and its corresponding averaged variance
  • Pump and impeller mask data
  • Additional data obtained from the SPS server with a sampling frequency of 1 Hz

Keywords: centrifugal pump; gas-liquid two-phase flow; ultrafast electron beam X-ray computed tomography

Downloads

Permalink: https://www.hzdr.de/publications/Publ-30370
Publ.-Id: 30370


Gas-liquid two-phase flow in a centrifugal pump mock-up with disperse gas flow injection at 1300 rpm

Bieberle, A.; Schäfer, T.
Project Member: Bieberle, Martina; Project Member: Neumann-Kipping, Martin; DataCollector: Wolf, Jan; Project Leader: Hampel, Uwe

This data repository contains reconstructed and quantitatively analyzed gas-liquid two-phase distributions obtained from a centrifugal pump mock-up whose geometry is related to a commercially available industrial centrifugal pump. As measurement system the ultrafast electron beam X-ray CT scanner (UFXCT) is applied with a frame rate of 2,500 Hz, single-plane mode and a total scanning interval of 5 seconds. The data repository contains:

  • Reconstructed raw data sets (Algebraic Reconstruction Technique from the UFO framework) for different inlet gas fractions (eps0.0xx) at constant 1300 rpm and for both rotating and back-rotated impeller positions, respectively
  • Extracted RPM per CT scan (frame) including its raw data
  • Extracted angular positions of the impeller mock-up per frame
  • Calculated quantitative gas fraction data sets (static impeller position)
  • Time-averaged gas fraction distribution and its corresponding averaged variance
  • Pump and impeller mask data
  • Additional data obtained from the SPS server with a sampling frequency of 1 Hz

Keywords: centrifugal pump; gas-liquid two-phase flow; ultrafast electron beam X-ray computed tomography

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Permalink: https://www.hzdr.de/publications/Publ-30369
Publ.-Id: 30369


Selective Adsorption of Pb(II) on an Annealed Hematite (1-102) Surface: Evidence from Crystal Truncation Rod X-ray Diffraction and Density Functional Theory

Qiu, C.; Chen, W.; Schmidt, M.; Majs, F.; Douglas, T. A.; Trainor, T. P.

The Pb(II) binding mechanism on an annealed hematite (11 ̅02) surface was studied using crystal truncation rod (CTR) X-ray diffraction coupled with density functional theory (DFT) calculations. The best fit CTR model suggested Pb(II) exhibited selective sorption to one specific type of edge-sharing surface site (ES2) over the other two types of potential surface sites. From the best fit model structure, it is found that the Pb surface complex species form a trigonal pyramid local geometry with the base consisting of three oxygen groups that include two surface O groups (IO and IIIO) and one distal O extending toward solution. The trigonal pyramid geometry is slightly distorted with Pb-O bond lengths ranging from 2.21 to 2.31 Å and O-Pb-O bond angles ranging from 72° to 75°. Under this structural distortion the nearest distance between Pb and Fe is found to be 3.39(1) Å. Consistent with the CTR results, DFT calculations indicate the Pb binding energy at the ES2 site is at least 0.06 eV stronger compared to the other two types of potential sites. Using bond-valence rules we propose a stoichiometry of Pb(II) binding on the hematite (11 ̅02) surface, which indicates proton release through the deprotonation of all oxygen groups bonding to Pb.

Keywords: Sorption; hematite; Surface X-ray Diffraction; CTR; DFT

Permalink: https://www.hzdr.de/publications/Publ-30368
Publ.-Id: 30368


Developments towards the detection of 135Cs and 137Cs by AMS

Wieser, A.; Lachner, J.; Martschini, M.; Steier, P.; Priller, A.; Honda, M.; Marchhart, O.; Golser, R.

The isotopic ratio ¹³⁵Cs/¹³⁷Cs can be used to assign sources of anthropogenic cesium input, as a geochemical tracer, or for modifying anthropogenic radionuclide dispersion models. Due to its long halflife, ¹³ ⁵Cs is hard to detect via decay counting. Mass Spectrometry has to deal with isobaric interferences, i.e. ¹³⁵Ba and ¹³⁷Ba for Cs detection. The new method of Ion Laser InterAction Mass Spectrometry (ILIAMS) at the Vienna Environmental Research Accelerator (VERA) overcomes this problem by exploiting differences in the electron affinites of CsF₂ and BaF₂ molecules.
A ¹³³CsF₂ current on the order of 100 nA from a mixed Cs₂SO₄ and PbF₂ - matrix is extracted from the ion source. The sample material is mobilized by heating the ionizer only, so no external sputtering material is needed. First results show reproducible detection of ¹³⁵Cs and ¹³⁷Cs in in-house reference materials. With 1mg stable Cs carrier, we reach a blank level of ¹³⁷Cs/¹³³Cs = 6 · 10−12, which corresponds to ≈ 30 mBq. We aim to lower this value by at least two orders of magnitude for measuring environmental samples.

Keywords: Accelerator Mass Spectrometry

Permalink: https://www.hzdr.de/publications/Publ-30367
Publ.-Id: 30367


Ion-irradiation-induced cobalt/cobalt oxide heterostructures: printing 3D interfaces

Yildirim, O.; Hilliard, D.; Arekapudi, S. S. P. K.; Fowley, C.; Cansever, H.; Koch, L.; Ramasubramanian, L.; Zhou, S.; Böttger, R.; Lindner, J.; Faßbender, J.; Hellwig, O.; Deac, A. M.

Interfaces separating ferromagnetic (FM) layers from non-ferromagnetic layers offer unique properties due to spin-orbit coupling and symmetry breaking, yielding effects such as exchange bias, perpendicular magnetic anisotropy, spin-pumping, spin-transfer torques, conversion between charge and spin currents and vice-versa. These interfacial phenomena play crucial roles for magnetic data storage and transfer applications, which require forming FM nano-structures embedded in non-ferromagnetic matrices. Here, we investigate the possiblity of creating such nano-structures by ion-irradiation. We study the effect of lateral confinement on the ion-irradiation-induced reduction of non-magnetic metal oxides (e.g., antiferro- or paramagnetic) to ferromagnetic metals. Our findings are later exploited to form 3-dimensional magnetic interfaces between Co, CoO and Pt by spatially-selective irradiation of CoO/Pt multilayers. We demonstrate that the mechanical displacement of the O atoms plays a crucial role during their reduction from insulating, non-ferromagnetic Co oxides to metallic Co. Metallic Co yields both perpendicular magnetic anisotropy in the generated Co/Pt nano-structures, and, at low temperatures, exchange bias at vertical interfaces between Co and CoO. If pushed to the limit of ion-irradiation technology, this approach could, in principle, enable the creation of densely-packed, atomic scale ferromagnetic point-contact spin-torque oscillator (STO) networks, or conductive channels for current-conned-path based current perpendicular-to-plane giant magnetoresistance read-heads.

Keywords: ion; irradiation; proton; cobalt oxide; CoO; Co3O4; paramagnetic; ferromagnetic; reduction; removal; oxygen; displacement; exchange; bias; magnetization; antiferromagnetic; perpencular; magnetic; anisotropy

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Permalink: https://www.hzdr.de/publications/Publ-30366
Publ.-Id: 30366


Visualisation of melt flow effects on dendritic solidification

Shevchenko, N.; Keplinger, O.; Eckert, S.

X-ray radioscopic studies have been performed to improve the understanding of the complex interrelation between melt flow and the evolution of dendritic structures during solidification of Ga-In alloys. Natural convection is caused by density variations within the solidifying alloys. Forced convection was produced by electromagnetic stirring. Within this work special interest was focused on dendrite fragmentation and segregation phenomena. Melt convection alters the solutal field near the solidification front, leading to different microstructures or even to the formation of freckle defects. Essential process parameters such as flow patterns, solute concentration, the mushy zone morphology and permeability, dendrite growth velocities were quantified by image analysis. Particular attention is paid to the development of segregation structures and to the “self-healing” process of segregation zones. The observations indicate that if the local melt flow near the solidification front is destabilized, the Indium-rich melt flows inside the channel. The consequence is the “self-healing” process, i.e. the channel is filled in a short time by new dendrites and finally disappears. Eventual mechanisms that destabilize the channel formation are discussed so that the freckle defect can be eliminated by electromagnetic stirring on early stage of solidification. Moreover, our experiments demonstrate how the melt flow contributes to grain refinement, the CET (columnar to equiaxed transition) and dendrite fragments transport, which are discussed intensively in the literature.

Keywords: Solidification; Ga-In alloy; Convection; Freckle defects

  • Lecture (Conference)
    5th International Conference on Advances in Solidification Processes (ICASP-5) & 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5), 17.-21.06.2019, Salzburg, Austria

Permalink: https://www.hzdr.de/publications/Publ-30365
Publ.-Id: 30365


Quantum radiation in dielectric media with dispersion and dissipation

Lang, S.; Schützhold, R.; Unruh, W.

By a generalization of the Hopfield model, we construct a microscopic Lagrangian describing a dielectric medium with dispersion and dissipation. This facilitates a well-defined and unambiguous ab initio treatment of quantum electrodynamics in such media, even in time-dependent backgrounds. As an example, we calculate the number of photons created by switching on and off dissipation in dependence on the temporal switching function. This effect may be stronger than quantum radiation produced by variations of the refractive index Δn(t) since the latter are typically very small and yield photon numbers of order (Δn)². As another difference, we find that the partner particles of the created medium photons are not other medium photons but excitations of the environment field causing the dissipation (which is switched on and off).

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Permalink: https://www.hzdr.de/publications/Publ-30364
Publ.-Id: 30364


Two Orders of Magnitude Boost in the Detection Limit of Droplet-Based Micro-Magnetofluidics with Planar Hall Effect Sensors

Schütt, J.; Illing, R.; Volkov, O.; Kosub, T.; Granell, P. N.; Nhalil, H.; Faßbender, J.; Klein, L.; Grosz, A.; Makarov, D.

Magnetofluidics is a dynamic research field, which requires novel sensor solutions to boost the detection limit of tiny quantities of magnetized objects. Here, we present a sensing strategy relying on planar Hall Effect (PHE) sensors in digital microfluidics for the detection of a multiphase liquid flow, i.e. superparamagnetic aqueous droplets in an oil carrier phase. The high resolution of the sensor allows the detection of nanoliter-sized superparamagnetic droplets with a concentration of 0.58 mg/cm³, even when they are biased in a geomagnetic field only. The limit of detection can be boosted another order of magnitude reaching 0.04 mg/cm³ (1.4 million particles in a single 100 nl droplet) when a magnetic field of 5 mT is applied to bias the droplets. With this performance, our sensing platform outperforms the state-of-the-art solutions in digital magnetofluidics by a factor of 100. This allows us to detect ferrofluid droplets in clinically and biologically relevant concentrations and even below without the need of externally applied magnetic fields. These results open the route for new strategies of the utilization of ferrofluids in microfluidic geometries in e.g. bio(-chemical) or medical applications.

Keywords: Droplet microfluidics; emulsion; planar Hall Effect; sensorics; microtechnology; contactless sensing; ferrofluids

  • Open Access Logo ACS Omega 5(2020), 20609
    Online First (2020) DOI: 10.1021/acsomega.0c02892
    Cited 5 times in Scopus
  • Lecture (Conference) (Online presentation)
    DPG Frühlingstagung, 22.-24.03.2021, Dresden, Deutschland
  • Lecture (Conference) (Online presentation)
    8th International Symposium on Sensor Science, 17.-28.05.2021, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30363
Publ.-Id: 30363


ADAM PETer – an anthropomorphic, deformable and multimodality pelvis phantom with positron emission tomography extension for radiotherapy

Gillmann, C.; Homolka, N.; Johnen, W.; Runz, A.; Echner, G.; Pfaffenberger, A.; Mann, P.; Schneider, V.; Hoffmann, A. L.; Troost, E. G. C.; Koerber, S. A.; Kotzerke, J.; Beuthien-Baumann, B.

Objective: To develop an anthropomorphic, deformable and multimodal pelvis phantom with positron emission tomography extension for radiotherapy (ADAM PETer).
Methods: The design of ADAM PETer was based on our previous pelvis phantom (ADAM) and extended for compatibility with PET and use in 3T magnetic resonance imaging (MRI). The formerly manually manufactured silicon organ surrogates were replaced by 3D printed organ shells. Two intraprostatic lesions, four iliac lymph node metastases and two pelvic bone metastases were added to simulate prostate cancer as multifocal and metastatic disease. Radiological properties (computed tomography (CT) and 3T MRI) of cortical bone, bone marrow and adipose tissue were simulated by heavy gypsum, a mixture of Vaseline and K2HPO4 and peanut oil, respectively. For soft tissues, agarose gels with varying concentrations of agarose, gadolinium (Gd) and sodium fluoride (NaF) were developed. The agarose gels were doped with patient-specific activity concentrations of a Fluorine-18 labelled compound and then filled into the 3D printed organ shells of prostate lesions, lymph node and bone metastases. The phantom was imaged at a dual energy CT and a 3T PET/MRI scanner.
Results: The compositions of the soft tissue surrogates are the following (given as mass fractions of agarose[w%]/NaF[w%]/Gd[w%]): Muscle (4/1/0.027), prostate (1.35/4.2/0.011), prostate lesions (2.25/4.2/0.0085), lymph node and bone metastases (1.4/4.2/0.025). In all imaging modalities, the phantom simulates human contrast. Intraprostatic lesions appear hypointense as compared to the surrounding normal prostate tissue in T2-weighted MRI. The PET signal of all tumors can be localized as focal spots at their respective site. Activity concentrations of 12.0 kBq/mL (prostate lesion), 12.4 kBq/mL (lymph nodes) and 39.5 kBq/mL (bone metastases) were measured.
Conclusion: The ADAM PETer pelvis phantom can be used as multimodal, anthropomorphic model for CT, 3T-MRI and PET measurements. It will be central to simulate and optimize the technical workflow for the integration of PET/MRI-based radiation treatment planning of prostate cancer patients.

Keywords: PET/MRI; prostate cancer; anthropomorphic pelvis phantom; anthropomorphic pelvis phantom

Permalink: https://www.hzdr.de/publications/Publ-30362
Publ.-Id: 30362


Off-shell Ward identities for N-gluon amplitudes

Ahmadiniaz, N.; Schubert, C.

Off-shell Ward identities in non-abelian gauge theory continue to be a subject of active research, since they are, in general, inhomogeneous and their form depends on the chosen gauge-fixing procedure. For the three-gluon and four-gluon vertices, it is known that a relatively simple form of the Ward identity can be achieved using the pinch technique or, equivalently, the background-field method with quantum Feynman gauge. The latter is also the gauge-fixing underlying the string-inspired formalism, and here we use this formalism to derive the corresponding form of the Ward identity for the one-loop N - gluon amplitudes.

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Permalink: https://www.hzdr.de/publications/Publ-30361
Publ.-Id: 30361


Waves in the magnetized spherical Couette problem.

Garcia Gonzalez, F.; Seilmayer, M.; Giesecke, A.; Stefani, F.

Experiments on the magnetized spherical Couette system are presently being carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid metal (GaInSn) is confined within two differentially rotating spheres and exposed to a magnetic field parallel to the axis of rotation. Bifurcation diagrams for rotating waves, obtained with continuation methods when only the magnetic field is increased, are presented. This allows us to carefully investigate the time-scales of the nonlinear saturation of the radial jet, return flow, and shear layer instabilities, as found in previous studies. In addition, modulated rotating waves, obtained at secondary bifurcations, are exhaustively studied by means of direct numerical simulations, with main focus on their spatio-temporal symmetries. We find that at moderate differential rotation the modulated rotating waves give rise to several types of chaotic flows, but only for the radial jet instability. With this study we reveal how the flow patterns and time-scales depend on the magnetic field, reproducing thus different physical situations of the HZDR experiments.

  • Poster
    Alexander von Humboldt Colloquium “Research without Borders – Alexander von Humboldt’s Legacy Today”, 11.-13.04.2019, Madrid, Spain

Permalink: https://www.hzdr.de/publications/Publ-30360
Publ.-Id: 30360


Experiments and simulations on the magnetized spherical Couette problem

Garcia Gonzalez, F.; Seilmayer, M.; Giesecke, A.; Stefani, F.

Experiments on the magnetized spherical Couette system are presently being carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid metal (GaInSn) is confined within two differentially rotating spheres and exposed to a magnetic field parallel to the axis of rotation. Bifurcation diagrams for rotating waves, obtained with continuation methods when only the magnetic field is increased, are presented. Bifurcation diagrams for modulated rotating waves and chaotic flows, obtained by means of DNS, are presented as well. This allows us to carefully investigate the nonlinear saturation of the radial jet, return flow, and shear layer instabilities, as found in previous studies. The main focus is on studing their spatio-temporal symmetries. We find that at moderate differential rotation the modulated rotating waves give rise to several types of chaotic flows, but only for the radial jet instability. With this study we reveal how the flow patterns and time-scales depend on the magnetic field, reproducing thus different physical situations of the HZDR experiments.

  • Poster
    Bursting the Bubble: Connecting Thermonuclear Burst Research to a Wider Community 2019, 24.-28.06.2019, Leiden, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-30359
Publ.-Id: 30359


The Hämmerlein skarn-greisen deposit in the Erzgebirge (Germany) - Analysis, geometallurgy and pre-concentration of a compositionally complex and fine-grained ore deposit

Kern, M.

The polymetallic Hämmerlein skarn-greisen deposit, located in the central portion of the Erzgebirge (Germany), is one of the most promising and prominent tin exploration targets in the world, with indium and zinc as potential by-products. The deposit has been discovered 50 years ago but has never been exploited, primarily because of the challenging beneficiation process. Currently, tin is mainly extracted from placer deposits in the Southeast Asian tin belt and in hydrothermal greisen deposit in China. Economic concentrations of tin are also found in metasomatically altered calc-silicate rocks called tin skarn, which is the predominant rock type at Hämmerlein. The exploitation of such deposits is usually challenging because of their complex mineralogy and fine-grained textures. As the currently mined easy-accessible and high-grade tin deposits are getting fewer, complex tin skarn orebodies have recently become the prime focus of tinexploration. The aim of this thesis is to characterize the ores from the Hämmerlein deposit and to evaluate the success of beneficiation experiments. This is achieved by developing an analytical procedure allowing for deportment analysis of complex ores, by combining geological and geometallurgical understanding of the Hämmerlein orebody, and by developing a novel data-driven approach to determine the optimal sensor that can be used for sensor-based sorting. A newly developed approach for the analysis of fine-grained complex ores combines mineralogical and chemical analysis using a Mineral Liberation Analyzer (MLA), electron probe microanalysis, X-ray powder diffraction, inductively-coupled plasma optical emission spectroscopy and X-ray fluorescence analysis to crushed and uncrushed samples. For MLA analysis, the conventional approach of creating a mineral reference list containing energy-dispersive X-ray (EDX) spectra and information about elemental concentrations and mineral densities did not achieve accurate results for the characterization of some of the samples analyzed. The fine-grained texture of the ore and the presence of a variety of tin-bearing minerals necessitate adding mineral references with manually mixed EDX-spectra, calculated elemental concentrations and calculated densities. Modal mineralogy and calculated assay data obtained by this modified approach for evaluating and processing MLA data is in very good agreement with results from bulk geochemistry and X-ray powder diffraction. The new approach can be adapted to calculate complex metal deportment of other mineralogically complex ore types containing a multitude of ore minerals. Quantitative MLA data from bulk samples and hand specimens are used to interpret the orebody from a geological and geometallurgical perspective. Analyzed samples exhibit considerable variability in modal mineral content and Sn deportment within the different lithounits of the deposit. The systematic differences between lithounits are VIII attributed to several stages of ore formation. The so-called MAMA ratio — a mineral association parameter that is calculated from automated mineralogy data — captures the cassiterite-chlorite-fluorite-sulfide assemblage. This assemblage is identified as the major source of tin in the deposit. It forms stockwork mineralization in greisen-type ores of the footwall and replaces pre-existing skarn lithologies in the hanging wall. These findings provide insight into the genesis of Sn mineralization and also yield important clues for beneficiation. Sensor-based sorting is the most promising technology to separate coarse barren particles from ore particles in the size range between 1 and 10 cm. A newly developed simulation-based approach is applied to find the optimal sensor for sensor-based sorting. Cassiterite is the single most important ore mineral, yet, it is only a very minor constituent (< 4 vol. %), which is heterogeneously distributed and fine-grained, ranging in size from 5 μm to 3 mm. Quantitative mineralogical and textural data from more than 100 thin sections acquired by MLA were taken to capture mineralogical and textural variability of the skarn ore and Schiefererz. Parameters from MLA datasets, such as mineral grain size distribution, modal mineralogy, mineral area and mineral density distribution are used to simulate the prospects of sensor-based sorting using different sensors. The results illustrate that the abundance of rock-forming chlorite and/or density anomalies may well be used as proxies for the abundance of cassiterite. Synchronization of MLA data and analysis of the same material with commercially available sensors illustrates excellent correspondence. Sorting of the Hämmerlein ore may well be achieved by using a shortwavelength infrared detector — to quantify the abundance of chlorite — or a dual-energy X-ray transmission detector to determine the abundance dense components. In summary, this thesis uses MLA data to assess the beneficiation potential of the Hämmerlein deposit by distinguishing between recoverable and unrecoverable Sn, evaluating processing strategies and by determining optimal sensors for sensor-based sorting. The presented approaches, beneficiation strategies and analytical procedures can be adapted for other ore types and have the potential to become standard technologies for the assessment of complex deposits.

  • Doctoral thesis
    TU Bergakademie Freiberg, 2019

Permalink: https://www.hzdr.de/publications/Publ-30358
Publ.-Id: 30358


Convection and magnetohydrodynamics in rotating spherical geometry: Simple models and their application to astrophysics

Garcia Gonzalez, F.

Spherical geometry and rotation are key factors for the study of many geophysical and astrophysical phenomena. In addition, strong temperature gradients develop in planetary and stellar fluid interiors. The Boussinesq approximation is a basic step for understanding flow dynamics in such environments. The formulation and numerical approach to this approximation in the context of thermal convection in rapidly rotating thin shells will be presented together with the main parameters describing the problem. The application to several geophysical (planetary atmospheres or cores) and astrophysical (white dwarfs, neutron stars...) contexts will be outlined.

As an example of simple magnetohydrodynamics problem, the magnetised spherical Couette system will be considered. Some interesting applications to the astrophysical community and advanced experiments of this problem will be commented.

  • Invited lecture (Conferences)
    Bursting the Bubble: Connecting Thermonuclear Burst Research to a Wider Community 2019, 24.-28.06.2019, Leiden, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-30357
Publ.-Id: 30357


Die Auswahl eines optimalen Sensors zur sensor-basierten Sortierung unter Anwendung automatisierter Mineralogie in Kombination mit Maschinellem Lernen

Kern, M.; Tusa, L.; Khodadadzadeh, M.; Leißner, T.; van den Boogaart, K. G.; Gloaguen, R.; Gutzmer, J.

Sensor-basierte Sortierung ist eine Technologie, die in zunehmendem Maße zur Aufbereitung von Primärrohstoffen verwendet wird. Um beurteilen zu können, ob der Einsatz sensor-basierter Sortierung zur Anreicherung eines bestimmten Erzes wirtschaftlich eingesetzt werden kann, werden nach Stand der Technik zeitaufwändige und teure empirische Teststudien durchgeführt. Mit dem hier vorgestellten innovativen simulations-basierten Ansatz ist es möglich, die Auswahl eines Sensors auf Grundlage von quantitativen mineralogischen und texturellen Daten zu treffen. Solche Daten können mit verfügbaren Methoden der automatisierten Mineralogie rasch und kostengünstig erhoben werden. Das dokumentierte Fallbeispiel basiert auf Daten aus mehr als 100 Dünnschliffen von zwei verschiedenen Erztypen aus der Sn-In-Zn Lagerstätte Hämmerlein, Erzgebirge. Die Proben wurden ausgewählt, um die mineralogische und texturelle Variabilität zu erfassen. Parameter wie Mineralkorngrößenverteilung, modale Mineralogie, Mineralflächen- und Mineraldichteverteilung wurden verwendet, um die Erfolgsaussichten einer sensorgestützten Sortierung mit verschiedenen Sensoren zu simulieren. Die Ergebnisse zeigen, dass die Häufigkeit von gesteinsbildendem Chlorit und/oder Dichteanomalien als Proxy für die Häufigkeit von Kassiterit, dem Haupterzmineral, verwendet werden können. Dies deutet darauf hin, dass die Sortierung des Hämmerlein-Erzes entweder mit einem Kurzwellen-Infrarotdetektor zur Quantifizierung des Chloritgehalts oder einem Dual-Energy-Röntgentransmissionsdetektor zur Abschätzung des Kassiteritgehalts erreicht werden kann. Die Abschätzung des Kassiteritgehalts einer Probe wurde durch Maschinelles Lernen optimiert, indem die Daten des Kurzwellen-Infrarot-Detektors mit den mineralogischen Daten integriert wurden. Dies führt zu einer weiteren, wichtigen Verbesserung der simulierten Ergebnisse. Empirische Tests mit handelsüblichen Sensorsystemen wurden genutzt, um die Vorhersagen der Simulationen experimentell zu validieren. Der entwickelte Ansatz kann sehr einfach auf andere Rohstofftypen angepasst werden; er birgt damit großes Potenzial, eine Schlüsseltechnologie zur Optimierung von Aufbereitungsprozessen zu werden.

  • Contribution to proceedings
    Tagung Aufbereitung und Recycling, 07.-8.11.2019, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30356
Publ.-Id: 30356


Experiments and simulations on the magnetized spherical Couette problem

Garcia Gonzalez, F.; Seilmayer, M.; Giesecke, A.; Stefani, F.

Experiments on the magnetized spherical Couette system are presently being carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid metal (GaInSn) is confined within two differentially rotating spheres and exposed to a magnetic field parallel to the axis of rotation. Bifurcation diagrams for rotating waves, obtained with continuation methods when only the magnetic field is increased, are presented. Bifurcation diagrams for modulated rotating waves and chaotic flows, obtained by means of DNS, are presented as well. This allows us to carefully investigate the nonlinear saturation of the radial jet, return flow, and shear layer instabilities, as found in previous studies. The main focus is on studing their spatio-temporal symmetries. We find that at moderate differential rotation the modulated rotating waves give rise to several types of chaotic flows, but only for the radial jet instability. With this study we reveal how the flow patterns and time-scales depend on the magnetic field, reproducing thus different physical situations of the HZDR experiments.

  • Poster
    11th pamir International Conference Fundamental and Applied MHD 2019., 01.-05.07.2019, Reims, France

Permalink: https://www.hzdr.de/publications/Publ-30355
Publ.-Id: 30355


Correction to. The inherent link between ore formation and geometallurgy as documented by complex tin mineralization at the Hämmerlein deposit (Erzgebirge, Germany)

Kern, M.; Kästner, J.; Tolosana Delgado, R.; Jeske, T.; Gutzmer, J.

We noticed that the presented formula for calculation of the MAMA ratio requires clarification in two places.

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Permalink: https://www.hzdr.de/publications/Publ-30354
Publ.-Id: 30354


Pair production in temporally and spatially oscillating fields

Aleksandrov, I. A.; Kohlfürst, C.

Electron-positron pair production for inhomogeneous electric and magnetic fields oscillating in space and time is investigated. By employing accurate numerical methods (Furry-picture quantization and quantum kinetic theory), final particle momentum spectra are calculated and analyzed in terms of effective models. Furthermore, criteria for the applicability of approximate methods are derived and discussed. In this context, special focus is placed on the local density approximation, where fields are assumed to be locally homogeneous in space. Eventually, we apply our findings to the multiphoton regime. Special emphasis is on the importance of linear momentum conservation and the effect of its absence in momentum spectra within approximations based on local homogeneity of the fields.

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Permalink: https://www.hzdr.de/publications/Publ-30353
Publ.-Id: 30353


Chaotic and oscillatory flows in the magnetized spherical Couette system.

Garcia Gonzalez, F.; Seilmayer, M.; Stefani, F.

Experiments on the magnetized spherical Couette system are presently being carried out at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). A liquid metal (GaInSn) is confined within two differentially rotating spheres and exposed to a magnetic field parallel to the axis of rotation. Bifurcation diagrams for modulated rotating waves and chaotic flows are obtained for investigating the nonlinear saturation of the radial jet, return flow, and shear layer instabilities, as found in previous studies.

  • Invited lecture (Conferences)
    9th International Congress on Industrial and Applied Mathematics, ICIAM 2019, 15.-19.07.2019, Valencia, Spain

Permalink: https://www.hzdr.de/publications/Publ-30352
Publ.-Id: 30352


The MAMA ratio: An index that quantifies genetic and geometallurgic relationships

Kern, M.; Kästner, J.; Tolosana Delgado, R.; Jeske, T.; Gutzmer, J.

A comprehensive quantitative mineralogical study on the Hämmerlein tin deposit in the Erzgebirge, Germany, yields not only insights into the genesis of Sn mineralization but provides also important clues for beneficiation. The lithological units of the skarn and greisen deposit show significant differences in modal mineralogy and Sn deportment. These systematic differences are attributed to several stages of ore formation. Of greatest significance is a paragenetically late cassiterite-chlorite-fluorite-sulfide assemblage. This assemblage replaces pre-existing skarn lithologies and also forms stockwork mineralization in greisen-type ores developed at the expense of mica schist that surrounds the skarn. The co-genetic formation of the cassiterite-chlorite-fluorite-sulfide assemblage is captured by the mineral association parameter – a parameter that can be easily quantified from data acquired during automated mineralogy studies. To document the preferred mineral association a ratio is introduced that illustrates how closely cassiterite – the only Sn mineral of economic relevance – is associated with chlorite, fluorite and sulfides. This so-called MAMA ratio illustrates the strongly preferred association between cassiterite and chlorite. The same data can also be used to deduce constraints and opportunities for beneficiation. The case study illustrates the inherent link between ore genesis and process mineralogy – a link that should be considered in any geometallurgical assessment.

  • Contribution to proceedings
    GOOD Meeting 2019, 22.-24.01.2019, Bremen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30351
Publ.-Id: 30351


On the effect of time-dependent inhomogeneous magnetic fields on the particle momentum spectrum in electron-positron pair production

Kohlfürst, C.

Electron-positron pair production in spatially and temporally inhomogeneous electric and magnetic fields is studied within the Dirac-Heisenberg-Wigner formalism (quantum kinetic theory) through computing the corresponding Wigner functions. The focus is on discussing the particle momentum spectrum regarding signatures of Schwinger and multiphoton pair production. Special emphasis is put on studying the impact of a strong dynamical magnetic field on the particle distribution functions. As the equal-time Wigner approach is formulated in terms of partial integro-differential equations an entire section of the manuscript is dedicated to present numerical solution techniques applicable to Wigner function approaches in general.

Permalink: https://www.hzdr.de/publications/Publ-30350
Publ.-Id: 30350


On self-created and self-creating dynamos

Stefani, F.

The lecture gives an overview about recent and future (self-created) liquid metal experiments on dynamo action and magnetically triggered flow instabilities. Some aspects of non-linear (self-creating) dynamos, in which induction and flow instabilities conspire to provide self-excitation, are also discussed.

  • Invited lecture (Conferences)
    11th PAMIR International Conference - Fundamental and Applied MHD, 01.-05.07.2019, Reims, France

Permalink: https://www.hzdr.de/publications/Publ-30349
Publ.-Id: 30349


Measure where protons stop in the patient: Verification of proton therapy by means of prompt gamma rays

Khamfongkhruea, C.; Nenoff, L.; Priegnitz, M.; Barczyk, S.; Berthold, J.; Vander Stappen, F.; Petzoldt, J.; Smeets, J.; Enghardt, W.; Pausch, G.; Richter, C.

Introduction
Proton therapy is the most advanced radiotherapeutic technique. For the same dose in the tumor, the dose in the surrounding normal tissue is substantially lower than in classical radiation therapy using photon beams. Protons stop in the patient and no dose is deposited behind that position. However, the resulting dose deposition is more sensitive to anatomical changes during treatment and to uncertainties in the CT-based range calculation. Therefore, monitoring of the proton range during treatment would substantially improve proton therapy. Prompt gamma radiation, which is emitted in nuclear reactions of the proton beam with the patient’s tissue, can be used to conclude on the proton range. The most translational advanced approach is prompt-gamma imaging (PGI) using a so-called slit camera [1]. A one-dimensional projection of the prompt-gamma distribution is acquired through a slit collimator onto a spatially resolved detector (Fig.1). The system, developed by IBA, is evaluated concerning its clinical benefit.

Materials and Methods
The PGI slit-camera was first enabled for routine clinical use by developing dedicated calibration and QA procedures as well as a clinical workflow and setting up a clinical study. In 2015, we were able to perform the first in-man PGI-based range verification [2], 13 years after the idea was initially proposed. In addition, the sensitivity and accuracy of the PGI slit-camera to detect different types of treatment deviations were evaluated for pencil-beam-scanning (PBS) proton therapy in an anthropomorphic phantom [3]. Following, a 2nd generation system was developed to improve positioning accuracy and reproducibility. Clinical application of this system in PBS proton therapy started in 2018.

Results
In the first in-man applications, detected inter-fractional global range variations were below ±2 mm, and thereby within the overall measurement uncertainties. This was verified with independent control CTs acquired directly before treatment. The phantom study revealed, that global and local range shifts can be detected with high sensitivity. Shift detection accuracy was better than 2 mm under clinical conditions. With the 2nd generation system, positioning uncertainty could be reduced to about 1 mm, potentially allowing a first in-man validation of the absolute range prediction as the measurement uncertainty is below the range prediction uncertainty.

Conclusion
With the translation from basic physics experiments into clinical operation, we were able to demonstrate the applicability of PGI-based range verification for improving the accuracy of proton therapy. Currently, we systematically evaluate the clinical benefit of the approach aiming for an automated detection of clinical relevant treatment deviation and classification of the underlying error source.

  • Poster
    1. German Cancer Research Congress - GCRC, 04.-05.02.2019, Heidelberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30348
Publ.-Id: 30348


Polar Waves and Chaotic Flows in Thin Rotating Spherical Shells

Garcia Gonzalez, F.; Chambers, F.; Watts, A.

Convection in rotating spherical geometries is an important physical process in planetary and stellar systems. Using continuation methods at a low Prandtl number, we find both strong equatorially asymmetric and symmetric polar nonlinear rotating waves in a model of thermal convection in thin rotating spherical shells with stress-free boundary conditions.
For the symmetric waves, convection is confined to high latitude in both hemispheres but is only restricted to one hemisphere close to the pole in the case of asymmetric waves. This is in contrast to what is previously known from studies in the field. These periodic flows, in which the pattern is rotating steadily in the azimuthal direction, develop a strong axisymmetric component very close to onset. Using stability analysis of periodic orbits, the regions of stability are determined and the topology of the stable/unstable oscillatory flows bifurcated from the branches of rotating waves is described. By means of direct numerical simulations of these oscillatory chaotic flows, we show that these three-dimensional convective polar flows exhibit characteristics, such as force balance or mean physical properties, which are similar to flows occurring in planetary atmospheres.
We show that these results may open a route to understanding unexplained features of gas giant atmospheres, particularly in the case of Jupiter. These include the observed equatorial asymmetry with a pronounced decrease at the equator (the so-called dimple), and the coherent vortices surrounding the poles recently observed by the Juno mission.

Keywords: Astrophysical fluid dynamics; Bifurcations; Convection; Geophysical fluid dynamics; Rotating geophysical flows

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Permalink: https://www.hzdr.de/publications/Publ-30347
Publ.-Id: 30347


Dual-energy computed tomography for improved proton therapy treatment planning

Peters, N.; Wohlfahrt, P.; Möhler, C.; Greilich, S.; Richter, C.

Purpose/Objective:

Cancer treatment with protons requires an accurate prediction of the particle’s range in tissue. In cCurrently clinical practice, computed tomography (CT) images are used to voxelwise translate the CT number into the tissue’s stopping power relative to water (SPR) via heuristic relations (HLUT). However, the general validity of this approach is limited due to the different physical interaction processes of photons and ions. The resulting range uncertainty is taken into account in the treatment plan by adding a safety margin around the tumor, effectively limiting the potential benefits of particle therapy over conventional radiotherapy. The use of dual-energy CT (DECT) allows for a direct derivation of tissue parameters, resulting in a better characterization of the tissue. The potential of a DECT-based,and ultimately allows a patient-individualized range prediction (DirectSPR) has been shown in previous work. In 2015, we were first to introduce DECT scans for routine clinical treatment planning, still using a generic HLUT. Here, we portray the next steps towards the full clinical implementation of DirectSPR, namely its validation and assessment of its clinical benefit.

Material and Methods:

To validate the method for realistic clinical scenarios, its accuracy was investigated in an anthropomorphic head phantom as well as in porcine biological tissue. Furthermore, intra- and inter-patient variabilities in CT-based SPR prediction were investigated in a retrospective analysis of 102 brain-tumor and 25 prostate-cancer patients. The clinical HLUT was then refined by performing a step-wise weighted linear fit of the resulting SPR distribution in different tissue regionsusing the DirectSPR information of the investigated patient cohort. To assess the effect of this refinement on the proton range within the patient, treatment plans were recalculated using the clinical HLUT, the refined HLUT as well as the DirectSPR approach.

Results:

In the complex head geometry, DirectSPR showed an improved accuracy compared to the clinical HLUT approach. For biological tissues in a simple geometry, an accuracy below 0.2% could be achieved. Between clinical HLUT and DirectSPR, mean range differences (±1SD) of (1.2±0.7)% for brain-cancer and (1.7±0.5)% for prostate-tumor patients were determined. By refining the HLUT, they were significantly reduced (p≪0.001, two-sample t-test) below 0.3%. HoweverMoreover, an observed intra-patient soft-tissue diversity of 6% as well as an inter-patient bone diversity of 5%, underline an additional benefit of the DirectSPR approach, as such variabilities cannot be considered by any generic HLUT-based range prediction.

Conclusions:

The clinical feasibility of DirectSPR for proton range prediction as well as its advantage over the HLUT approach has been demonstrated. A retrospective application on patient data allowed for a reduction of systematic deviations found in clinical HLUT. The refined HLUT was implemented at our institution as a step towards the currently ongoing full integration of DirectSPR. The Its higher precision accuracy in range prediction is reflected in a potentially allows a reduction of the safety margin, which is currently under investigation.

  • Poster
    1. German Cancer Research Congress GCRC, 04.-05.02.2019, Heidelberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30346
Publ.-Id: 30346


A model for tidal synchronization and modulation of the solar dynamo

Stefani, F.; Giesecke, A.; Weier, T.

We present a solar dynamo model of Tayler-Spruit type with an Omega-effect that is conventionally produced by solar-like differential rotation, while its alpha-effect is periodically modulated by planetary tidal forcing. The underlying resonance builds upon the tendency of the Tayler instability to generate helicity oscillations which can be synchronized by periodic tidal forces. We focus on the 11.07 years alignment periodicity of the planets Venus, Earth, and Jupiter and analyze its synchronization with the solar dynamo. The typically emerging dynamo modes are dipolar or quadrupolar fields, oscillating with a 22.14 years period or pulsating with a 11.07 years period. When starting from a conventional alpha-Omega-dynamo, the addition of the periodic alpha-part can lead to entrainment of the entire dynamo via parametric resonance. Phase coherent transitions between dipoles and quadrupoles are discussed, too.

  • Lecture (Conference)
    11th PAMIR International Conference - Fundamental and Applied MHD, 01.-05.07.2019, Reims, France
  • Contribution to proceedings
    11th PAMIR International Conference - Fundamental and Applied MHD, 01.-05.07.2019, Reims, France
    Proceedings of the 11th PAMIR International Conference - Fundamental and Applied MHD, Reims, France: University of Reims Champagne-Ardenne, 43-47

Permalink: https://www.hzdr.de/publications/Publ-30345
Publ.-Id: 30345


Dual Energy - Stopping Power Ratio: Facilitating clinical implementation of Dual Energy CT-based stopping power prediction – What‘s the benefit?

Richter, C.; Möhler, C.

Facilitating clinical implementation of Dual Energy CT-based stopping power prediction – What‘s the benefit?

  • Invited lecture (Conferences)
    Siemens Healthineers Lunch Symposium at ESTRO 38, 29.04.2019, Milano, Italia

Permalink: https://www.hzdr.de/publications/Publ-30344
Publ.-Id: 30344


CT-based delineation: What can we gain from state-of-the-art CT image acquisition and reconstruction techniques?

Richter, C.; Negwer, F.; Troost, E. G. C.; Wohlfahrt, P.

X-ray computed tomography (CT) has been the standard imaging modality in radiation oncology for both, treatment planning and delineation of targets and organs at risk for decades. For further improvement, especially for delineation, magnetic resonance imaging (MRI) and positron emission tomography (PET) are being extensively investigated and more often included into clinical routines. They can provide better soft tissue contrast and functional information. Still, also in the field of CT imaging relevant improvements have been made, that are not so much in the spotlight. Hence, this talk will focus on novel CT image acquisition and reconstruction techniques and their potential benefit for radiation oncology applications.
First, the potential value of dual-energy CT (DECT) for delineation will be discussed. DECT has already been proven to allow for a more accurate treatment planning, especially in particle therapy. It provides additional tissue information compared to conventional CT imaging. Furthermore, DECT enables the reconstruction of different CT datasets with varying image contrasts. Currently, it is unproven whether this additional information translates into improvement of the segmentation and delineation quality. The exploration of this benefit in combination with machine learning approaches is envisioned. First studies will be presented.
Second, the potential of iterative CT reconstruction methods will be highlighted. They allow for a substantial reduction of imaging dose to reach a similar noise level as conventional filtered back projection. Hence, iterative reconstruction is of high relevance for adaptive protocols as it reduces the dose burden from more frequent CT imaging during treatment.
Third, the value and challenges of metal artefact reduction algorithms will be covered. It has been shown that the visual image impression can be substantially improved for regions suffering from metal artefacts in conventional CT reconstruction, suggesting a direct benefit for delineation purposes. However, as these algorithms can also quantitatively alter the image in regions not influenced by metal artefacts, great care should be taken – especially in particle therapy planning.
In summary, state-of-the-art CT imaging can provide additional value for radiation oncology purposes. This talk aims to increase awareness of this potential. By revisiting the institutional imaging protocol, one can potentially improve the image quality for delineation and/or safe dose to patients.

  • Invited lecture (Conferences)
    ESTRO 38, 26.-30.04.2019, Milano, Italia
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 133(2019), S361-S361
    DOI: 10.1016/S0167-8140(19)31118-1

Permalink: https://www.hzdr.de/publications/Publ-30343
Publ.-Id: 30343


Translational medical physics research: Increasing accuracy in particle therapy towards its physical limit

Richter, C.

Translational medical physics research: Increasing accuracy in particle therapy towards its physical limit

  • Invited lecture (Conferences)
    Sino-German Round Table Symposium on Cancer Precision Medicine in the Era of Big Data, 19.-20.06.2019, Tianjin, China

Permalink: https://www.hzdr.de/publications/Publ-30342
Publ.-Id: 30342


Bildgeführte Teilchentherapie und Bestrahlungs-Verifizierung

Richter, C.

Bildgeführte Teilchentherapie und Bestrahlungs-Verifizierung

  • Invited lecture (Conferences)
    Fachkundekurs und Aktualisierungskurs für die Partikeltherapie, 07.-09.11.2019, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-30341
Publ.-Id: 30341


Dual-Energy CT for particle therapy planning and beyond

Richter, C.

Dual-Energy CT for particle therapy planning and beyond

  • Invited lecture (Conferences)
    ESTRO School: Imaging for Physicists, 29.09.-03.10.2019, Manchester, United Kingdom
  • Lecture (Conference)
    ESTRO School: Imaging for physicists, 14.04.-19.05.2021, online, online

Permalink: https://www.hzdr.de/publications/Publ-30340
Publ.-Id: 30340


CT-based in-room imaging

Richter, C.

CT-based in-room imaging

  • Invited lecture (Conferences)
    ESTRO School: Imaging for Physicists, 29.09.-03.10.2019, Manchester, United Kingdom
  • Lecture (Conference)
    ESTRO School: Imaging for physicists, 14.04.-19.05.2021, online, online

Permalink: https://www.hzdr.de/publications/Publ-30339
Publ.-Id: 30339


CT for radiotherapy planning

Richter, C.

CT for radiotherapy planning

  • Invited lecture (Conferences)
    ESTRO School: Imaging for Physicists, 29.09.-03.10.2019, Manchester, United Kingdom
  • Lecture (Conference)
    ESTRO Imaging for physicists, 14.04.-19.05.2021, online, online

Permalink: https://www.hzdr.de/publications/Publ-30338
Publ.-Id: 30338


Clinical implementation of TPS-independent DECT-based patient-individual SPR prediction and its way into Raystation

Richter, C.; Wohlfahrt, P.

Clinical implementation of TPS-independent DECT-based patient-individual SPR prediction and its way into Raystation

  • Invited lecture (Conferences)
    Raysearch Particle Premeeting at PTCOG, 12.06.2019, Manchester, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-30337
Publ.-Id: 30337


The DRESDYN Project at HZDR

Stefani, F.; Eckert, S.; Gerbeth, G.; Giesecke, A.; Seilmayer, M.; Vogt, T.

We discuss the background and the recent status of the DRESDYN project at HZDR. Special focus is laid on the relation with sodium flow problems specific to SFR's.

  • Lecture (Conference)
    ESFR-SMART workshop on Instrumentation for the Safety of Liquid Metal Facilities, 10.-12.04.2019, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-30336
Publ.-Id: 30336


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