Gupta Deeksha, Pankratova Maryna, Riepp Matthias, Pereiro Manuel, Sanyal Biplab, Ershadrad Soheil, Hehn Michel, Pontius Niko, Schüßler-Langeheine Christian, Abrudan Radu, Bergeard Nicolas, Bergman Anders, Eriksson Olle, Boeglin Christine
Institut de Physique et de Chimie des Matériaux de Strasbourg, UMR7504, CNRS et Université de Strasbourg, Strasbourg, France.
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein Str. 15, Berlin, Germany.
Nat Commun. 2025 Mar 31;16(1):3097. doi: 10.1038/s41467-025-58411-3.
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 FeGd 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 FeGd 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.
飞秒激光脉冲可用于诱导磁性材料中磁化强度的超快变化。人们提出了几种微观机制来解释这些现象，包括超短自旋极化热电子（SPHE）的输运。然而，由于对元素和时间分辨率的测量要求，目前这种超快自旋电流的特征还很不明确。在此，我们利用时间分辨和元素分辨的X射线磁圆二色性以及原子自旋动力学模拟，研究了自旋极化电流中角动量的超快转移。我们表明，在自旋阀结构中使用Co/Pt多层膜作为偏振器时，SPHE会驱动FeGd薄膜两个子晶格的退磁。这种行为可以用两种物理机制来解释：自旋转移力矩和SPHE引起的热涨落。我们对超短SPHE脉冲向FeGd薄膜的热传递以及导致所观察到的磁化动力学的SPHE电流密度的自旋极化效应进行了定量描述。我们的工作最终表征了SPHE的自旋极化，揭示了与Co磁化方向出乎意料的相反自旋极化。
