Joint press release of Mittweida University of Applied Sciences and HZDR of December 7, 2023

Magnetization by laser pulse

Research team identifies new details of a promising phenomenon

To magnetize an iron nail, one simply has to stroke its surface several times with a bar magnet. Yet, there is a much more unusual method: A team led by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) discovered some time ago that a certain iron alloy can be magnetized with ultrashort laser pulses. The researchers have now teamed up with the Laserinstitut Hochschule Mittweida (LHM) to investigate this process further. They discovered that the phenomenon also occurs with a different class of materials – which significantly broadens potential application prospects. The working group presents its findings in the scientific journal Advanced Functional Materials (DOI: 10.1002/adfm.202311951).

The unexpected discovery was made back in 2018. When the HZDR team irradiated a thin layer of an iron-aluminum alloy with ultrashort laser pulses, the non-magnetic material suddenly became magnetic. The explanation: The laser pulses rearrange the atoms in the crystal in such a way that the iron atoms move closer together, and thus forming a magnet. The researchers were then able to demagnetize the layer again with a series of weaker laser pulses. This enabled them to discover a way of creating and erasing tiny "magnetic spots" on a surface.

However, the pilot experiment still left some questions unanswered. "It was unclear whether the effect only occurs in the iron-aluminum alloy or also in other materials," explains Dr. Rantej Bali, physicist at the Institute of Ion Beam Physics and Materials Research at HZDR. "We also wanted to try tracking the time progression of the process." For further investigation, he teamed up with Prof. Alexander Horn and Dr. Theo Pflug from the LHM as well as colleagues from the University of Zaragoza in Spain.

Flip book with laser pulses

The experts focused specifically on an iron-vanadium alloy. Unlike the iron-aluminum alloy with its regular crystal lattice, the atoms in the iron-vanadium alloy are arranged more chaotically, forming an amorphous, glass-like structure. In order to observe what happens upon laser irradiation, the physicists used a special method: The pump-probe method.

"First, we irradiate the alloy with a strong laser pulse, which magnetizes the material," explains Theo Pflug. "Simultaneously, we use a second, weaker pulse that is reflected on the material surface."

The analysis of the reflected laser pulse provides an indication of the material's physical properties. This process is repeated several times, whereby the time interval between the first "pump" pulse and the subsequent "probe" pulse is continually extended.

As a result, a time series of reflection data is obtained, which allows to characterize the processes being triggered by the laser excitation. "The whole procedure is similar to generating a flip book," says Pflug. "Likewise, a series of individual images that animate when viewed in quick succession."

Rapid melting

The result: Although it has a different atomic structure than the iron-aluminum compound, the iron-vanadium alloy can also be magnetized via laser. "In both cases, the material melts briefly at the irradiation point", explains Rantej Bali. "This causes the laser to erase the previous structure so that a small magnetic area is generated in both alloys."

An encouraging result: Apparently, the phenomenon is not limited to a specific material structure but can be observed in diverse atomic arrangements.

The team is also keeping track of the temporal dynamics of the process: "At least we now know in which time scales something happens," explains Theo Pflug. "Within femtoseconds, the laser pulse excites the electrons in the material. Several picoseconds later, the excited electrons transfer their energy to the atomic nuclei."

Consequently, this energy transfer causes the rearrangement into a magnetic structure, which is stabilized by the subsequent rapid cooling. In follow-up experiments, the researchers aim to observe exactly how the atoms rearrange themselves by examining the magnetization process with intense X-rays.

Sights set on applications

Although still in the early stages, this work already provides initial ideas for possible applications: For example, placing tiny magnets on a chip surface via laser is conceivable. "This could be useful for the production of sensitive magnetic sensors, such as those used in vehicles," speculates Rantej Bali. "It could also find possible applications in magnetic data storage."

Additionally, the phenomenon appears relevant for a new type of electronics, namely spintronics. Here, magnetic signals should be used for digital computing processes instead of electrons passing through transistors as usual – offering a possible approach to computer technology of the future.

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Publication:

T. Pflug, J. Pablo-Navarro, S. Anwar, M. Olbrich, C. Magén, M. R. Ibarra, K. Potzger, J. Faßbender, J. Lindner, A. Horn, R. Bali: Laser-Induced Positional and Chemical Lattice Reordering Generating Ferromagnetism, Advanced Functional Materials, 2023 (DOI: 10.1002/adfm.202311951)

Further information:

Dr. Rantej Bali
Institute of Ion Beam Physics and Materials Research at HZDR
Phone: +49 351 260 2919 | Email: r.bali@hzdr.de

Dr. Theo Pflug
Research group of Prof. Alexander Horn – Laserinstitut Hochschule Mittweida
Phone: +49 3727 58 1894 | Email: pflug@hs-mittweida.de

Media contact:

Simon Schmitt | Head
Communications and Media Relations at HZDR
Phone: +49 351 260 3400 | Email: s.schmitt@hzdr.de

Helmut Hammer | Press spokesperson
Rectorate | University communications
Hochschule Mittweida | University of Applied Sciences
Technikumplatz 17 | 09648 Mittweida | Germany
Phone: +49 3727 58-1226 | +49 175 68 48 817 | Email: presse@hs-mittweida.de

The Laserinstitut Hochschule Mittweida (LHM) is a central scientific facility at Mittweida University of Applied
Sciences. It is one of the leading research institutes in the field of laser technology in Germany and the only one at a University of Applied Sciences (UAS). The LHM's research areas include laser micro and nano processing, laser-based additive manufacturing, pulsed laser deposition (PLD), laser metrology, modelling and simulation of laser processes as well as laser bionics and biophotonics. Around 50 experts pursue an application-oriented research that is recognized worldwide. Inaugurated in 2016, the LHM institute building with more than 2,500 square meters of research space is the first new research building at a UAS to be co-financed by a federal-state program in Germany.