Research: Ultra Fast Change of Volume Discovered in Magnetic Materials

2018-01-26

All magnetic materials show a change of volume if their magnetization changes, but how the process takes place on the shortest time scales is still a mystery. To understand how magnetic changes of volume occur inside the femtosecond range (10-15s) one needs both new measurement methods and novel theories. An international collaboration of both experimental and theoretical research groups has now managed to come a step closer to the solution of this riddle.

What they have managed to measure is how the volume of nanoparticles of iron-platinum changes by transforming the spin-magnetic state of the material, so called magnetostriction, on ultra-short time scales, within picoseconds (10-12 s). The new results have been published in the journal Nature Communications.

The Uppsala researcher Hermann Dürr has together with researchers from the USA, Japan, Germany and Czech Republic and also companies, such as IBM and Western Digital, used a new experimental technique, so called ultra-fast electron scattering, to be able to measure dynamic length variations in all three nanoparticle dimensions.

Electron pulses, shorter than 100
femtoseconds, are aimed at the
nanoparticles of iron-platinum and
a three-dimensional tomography of
how the electrons scatter is depicted
on the detector screen.
Figure: Alex Reid.

The experimental technique entails that an ultra-short laser pulse is aimed at the nanoparticles of iron-platinum, which then lose their magnetization due to the fact that the electrons in the material are excited and that the material ends up in a state very far from equilibrium. Thereafter electron pulses, as short as 100 femtoseconds, are aimed at the material and the way electrons scatter off the nanoparticles allowed for the first time to observe oscillation in the particle volume. This is very similar to making a bell ring but now it is the loss of magnetization that is causing the ringing.

The Uppsala physicists Pablo Maldonado and Peter Oppeneer have developed a new theory which provides detailed insight into how magnetostriction builds up caused by the non-equilibrium energy flow between electrons, lattice atoms and the iron-platinum magnetization. These results are especially important for the magnetic hard disk industry since iron-platinum nanoparticles are considered the most promising storage medium for the high capacity hard disk drives of the future.

– Our experiments have been able to show the potential electron scattering has for ultrafast volume changes. I hope to be able to build measurement instruments for ultrafast electron diffraction in the FREIA-laboratory at Uppsala University and develop it as a center for interdisciplinary research, where it is possible to combine ultrafast structure tomography and theory for dynamical processes, says Hermann Dürr who recently was recruited from Stanford to become professor at the Department of Physics and Astronomy.

Article Reference

Beyond a phenomenological description of magnetostriction, A. H. Reid, X. Shen, P. Maldonado et al., Nature Communications, DOI:10.1038/s41467-017-02730-7

Contact

Prof. Hermann Dürr, telefon 0704-250176, herman.durr@physics.uu.se
Dr. Pablo Maldonado, pablo.maldonado@physics.uu.se
Prof. Peter Oppeneer, peter.oppeneer@physics.uu.se,
all of them at the Department of Physics and Astronomy, Uppsala University.

Camilla Thulin

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