Signatures of longitudinal spin pumping in a magnetic phase transition

Taekhyeon Lee, Min Tae Park, Hye-Won Ko, Jung Hyun Oh, San Ko, Seongmun Hwang, Jae Gwang Jang, Geon-Woo Baek, Se Kwon Kim, Hyun-Woo Lee, Myung-Hwa Jung (), Kab-Jin Kim () and Kyung-Jin Lee ()
Additional contact information
Taekhyeon Lee: Korea Advanced Institute of Science and Technology (KAIST)
Min Tae Park: Sogang University
Hye-Won Ko: Korea Advanced Institute of Science and Technology (KAIST)
Jung Hyun Oh: Korea Advanced Institute of Science and Technology (KAIST)
San Ko: Korea Advanced Institute of Science and Technology (KAIST)
Seongmun Hwang: Korea Advanced Institute of Science and Technology (KAIST)
Jae Gwang Jang: Korea Advanced Institute of Science and Technology (KAIST)
Geon-Woo Baek: Korea Advanced Institute of Science and Technology (KAIST)
Se Kwon Kim: Korea Advanced Institute of Science and Technology (KAIST)
Hyun-Woo Lee: Pohang University of Science and Technology
Myung-Hwa Jung: Sogang University
Kab-Jin Kim: Korea Advanced Institute of Science and Technology (KAIST)
Kyung-Jin Lee: Korea Advanced Institute of Science and Technology (KAIST)

Nature, 2025, vol. 638, issue 8049, 106-111

Abstract: Abstract A particle current generated by pumping in the absence of gradients in potential energy, density or temperature1 is associated with non-trivial dynamics. A representative example is charge pumping that is associated with the quantum Hall effect2 and the quantum anomalous Hall effect3. Spin pumping, the spin equivalent of charge pumping, refers to the emission of a spin current by magnetization dynamics4–7. Previous studies have focused solely on transversal spin pumping arising from classical dynamics, which corresponds to precessing atomic moments with constant magnitude. However, longitudinal spin pumping arising from quantum fluctuations, which correspond to a temporal change in the atomic moment’s magnitude, remains unexplored. Here we experimentally investigate longitudinal spin pumping using iron–rhodium (FeRh), which undergoes a first-order antiferromagnet-to-ferromagnet phase transition during which the atomic moment’s magnitude varies over time. By injecting a charge current into a FeRh/platinum bilayer, we induce a rapid phase transition of FeRh in nanoseconds, leading to the emission of a spin current to the platinum layer. The observed inverse spin Hall signal is about one order of magnitude larger than expected for transversal spin pumping, suggesting the presence of longitudinal spin pumping driven by quantum fluctuations and indicating its superiority over classical transversal spin pumping. Our result highlights the significance of quantum fluctuations in spin pumping and holds broad applicability in diverse angular momentum dynamics, such as laser-induced ultrafast demagnetization8, orbital pumping9,10 and quantum spin transfer11–13.

Date: 2025
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DOI: 10.1038/s41586-024-08367-z

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