Unveiling Orbital-mediated Ultrafast Demagnetization in Rare Earth-Transition-Metal Ferrimagnets

Jianwen Gao; Linlin Zhang; Mingli Ge; Runhua Zhang; Jinshan Wang; Hui Li; Xiaowei Zhou; Zhu Liu; Zongzhi Zhang; Li Xi; Yalu Zuo; Chenglong Jia; Feng Qiu; Shaojie Hu; Yang Ren

arXiv · 2606.11591

Unveiling Orbital-mediated Ultrafast Demagnetization in Rare Earth-Transition-Metal Ferrimagnets

Jianwen Gao·Linlin Zhang·Mingli Ge·Runhua Zhang·Jinshan Wang·Hui Li·Xiaowei Zhou·Zhu Liu·Zongzhi Zhang·Li Xi·Yalu Zuo·Chenglong Jia·Feng Qiu·Shaojie Hu·Yang Ren

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Abstract

The ultimate speed limit of magnetic recording and spintronic devices is set by the efficiency of angular-momentum transfer during ultrafast demagnetization, yet its microscopic pathway in Rare-Earth-Transition-Metal (RE-TM) ferrimagnets remains debated. Here, we establish an orbital-mediated framework in which 3d spin-orbit coupling (SOC) governs angular momentum (AM) dissipation. Strong 3d-SOC in RE-Co enables sub-picosecond, single-step demagnetization via direct orbital-to-lattice transfer, whereas weak 3d-SOC in RE-Fe redirects AM into 4f orbitals, producing slower two-step dynamics. The second-stage rate scales with 4f-SOC strength, revealing a distinct orbital-mediated dissipation channel. Using time-resolved magneto-optical Kerr measurements, supported by an extended four-temperature model, corroborate this picture across diverse RE-TM systems (RE = Sm, Gd, Tb, Dy, Ho and TM = Fe, Co, CoNi). Our results identify the SOC-driven competition between 3d and 4f orbital channels as the universal mechanism governing ultrafast demagnetization in RE-TM ferrimagnets, enabling rational design of the switching speed for next-generation spintronic devices.

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Jianwen Gao, Linlin Zhang, Mingli Ge, Runhua Zhang, Jinshan Wang, Hui Li, Xiaowei Zhou, Zhu Liu, Zongzhi Zhang, Li Xi, Yalu Zuo, Chenglong Jia, Feng Qiu, Shaojie Hu, Yang Ren. 2026-06-10. Unveiling Orbital-mediated Ultrafast Demagnetization in Rare Earth-Transition-Metal Ferrimagnets. https://arxiv.org/abs/2606.11591

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