Structure induced magnetic transitions for hybrid magnetic materials (in-house)
Our research focusses on understanding the mechanism of disorder induced magnetic transitions, and attempts to exploit such transitions for creating spin-transport and spin-wave devices based on hybrid architectures. Magnetic properties can depend sensitively on the arrangement of atoms in alloys, typically composed of a 3d magnetic metal with a non-magnetic metal. Ion-beams are highly effective tools for randomizing the atomic arrangement in alloys, in a controllable way, and varying the nearest neighbour interactions between the magnetic atoms. Huge changes in the saturation magnetization of some alloys can be observed by varying the atomic arrangement.
A salient example of ion-induced magnetic phase transition is observed in Fe60Al40 alloy thin films. The figure below shows the low saturation magnetization observed on the chemically ordered Fe60Al40 thin films (left), and the factor of 40 increase observed on the film after ion irradiation (right).
Magnetic phase transitions can be induced at the nanoscale using ion-irradiation through lithographed masks, or using a focussed ion-beam as a stylus. The sketch below depicts the fabrication of neary-discrete ferromagnetic stripes, separated by ~ 40 nm wide weakly magnetic spacers, obtained by locally inducing chemical disorder. The magnet/spacer/magnet structure can exhibit reprogrammable parallel (↑/spacer/↑) and antiparallel (↑/spacer/↓) magnetic states, and is a step towards achieving a laterally patterned spin-valve .
- Nano-magnetic patterning for spin-transport and spin-wave device applications
- Engineering the metamagnetic phase transition in FeRh
- Dr Rantej Bali (spokesperson)
- Alireza Heidarian
- Dr Kay Potzger (senior scientist)
- Prof Adekunle Adeyeye, National University of Singapore
- Prof Jürgen Bauch, Technische Universität Dresden
- Dr Florian Kronast, Helmholtz-Zentrum Berlin
- Dr Peter Metaxas & Prof Mikhail Kostylev, University of Western Australia
- Dr Falk Röder & Prof Hannes Lichte, Triebenberg Laboratory, Technische Universität Dresden
- Prof Andrzej Maziewski, University of Białystok
- Dr Alevtina Smekhova, Lomonosov Moscow State University
- Dr Hartmut Stöcker, TUBA Freiberg
- Dr Enric Menendez, University of LEuven, Belgium
Chemically ordered Fe-Al alloys are paramagnetic whereas disordered alloys are ferromagnetic. Disorder can be induced by ion-irradiation as seen in the hysteresis loops of Fig. 1 [2,3]. By means of local ion treatment, ferromagnetic micro- or nanostructures can be created within a paramagnetic matrix (Fig. 2).
Fig. 1: Hysteresis loops of Fe60Al40 measured after irradiation with varying dosage.
Fig. 2: a) Flat topography of Fe60Al40 sheets seen using Atomic Force Microscopy, and b) magnetic contrast observed using Magnetic Force Microscopy showing magnetically patterned array. c) and d) show magnetic contrast under applied magnetic field indicated by the arrows. All micrographs are 7.5 x 7.5 microns2 scale.
 Printing Nearly-Discrete Magnetic Patterns Using Chemical Disorder Induced Ferromagnetism, Rantej Bali, Sebastian Wintz, Falk Meutzner, René Hübner, Richard Boucher, Ahmet A. Ünal, Sergio Valencia, Andreas Neudert, Kay Potzger, Jürgen Bauch, Florian Kronast, Stefan Facsko, Jürgen Lindner, and Jürgen Fassbender, Nano Letters 2014, (http://pubs.acs.org/doi/abs/10.1021/nl404521c).
 Ion mass dependence of irradiation-induced local creation of ferromagnetism in Fe60Al40 alloys, J. Fassbender, M. O. Liedke, T. Strache, W. Möller, E. Menéndez, J. Sort, K. V. Rao, S. C. Deevi, and J. Nogués, Phys. Rev. B 2008, 77, 174430.
 Direct Magnetic Patterning due to the Generation of Ferromagnetism by Selective Ion Irradiation of Paramagnetic FeAl Alloys, Enric Menéndez, Maciej Oskar Liedke, Jürgen Fassbender, Thomas Gemming, Anja Weber, Laura J. Heyderman, K. V. Rao, Seetharama C. Deevi, Santiago Suriñach, Maria Dolors Baró, Jordi Sort, and Josep Nogués, Small 2009, 5, No. 2, 229–234