Tuning ultrafast demagnetization with ultrashort spin polarized currents in multi-sublattice ferrimagnets

Deeksha Gupta, Maryna Pankratova, Matthias Riepp, Manuel Pereiro, Biplab Sanyal, Soheil Ershadrad, Michel Hehn, Niko Pontius, Christian Schüßler-Langeheine, Radu Abrudan, Nicolas Bergeard, Anders Bergman, Olle Eriksson and Christine Boeglin ()
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Deeksha Gupta: CNRS et Université de Strasbourg
Maryna Pankratova: Uppsala University
Matthias Riepp: CNRS et Université de Strasbourg
Manuel Pereiro: Uppsala University
Biplab Sanyal: Uppsala University
Soheil Ershadrad: Uppsala University
Michel Hehn: Institut Jean Lamour, UMR 7198 CNRS
Niko Pontius: Albert-Einstein Str. 15
Christian Schüßler-Langeheine: Albert-Einstein Str. 15
Radu Abrudan: Albert-Einstein Str. 15
Nicolas Bergeard: CNRS et Université de Strasbourg
Anders Bergman: Uppsala University
Olle Eriksson: Uppsala University
Christine Boeglin: CNRS et Université de Strasbourg

Nature Communications, 2025, vol. 16, issue 1, 1-10

Abstract: Abstract Femtosecond laser pulses can be used to induce ultrafast changes of the magnetization in magnetic materials. Several microscopic mechanisms have been proposed to explain these observations, including the transport of ultrashort spin-polarized hot-electrons (SPHE). However, currently such ultrafast spin currents are only poorly characterized due to the measurement requirements for element and time resolution. Here, using time- and element-resolved X-ray magnetic circular dichroism alongside atomistic spin-dynamics simulations, we study the ultrafast transfer of the angular momentum from spin-polarized currents. We show that using a Co/Pt multilayer as a polarizer in a spin-valve structure, the SPHE drives the demagnetization of the two sub-lattices of the Fe74Gd26 film. This behaviour can be explained with two physical mechanisms; spin transfer torque and thermal fluctuations induced by the SPHE. We provide a quantitative description of the heat transfer of the ultrashort SPHE pulse to the Fe74Gd26 films, as well as the effect of spin-polarization of the SPHE current density responsible for the observed magnetization dynamics. Our work finally characterizes the spin-polarization of the SPHEs revealing unexpected opposite spin polarization to the Co magnetization.

Date: 2025
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DOI: 10.1038/s41467-025-58411-3

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