Sign reversal of ST-FMR signals in CoFeB/Pt explained by contributions beyond spin-orbit torque
Abstract
Spin-orbit torques (SOT) provide an efficient route for electrical control of magnetization and is of central interest for low-power magnetic memory applications. Spin-torque ferromagnetic resonance (ST-FMR) is a widely used technique to quantify SOT efficiencies. However, the rectified voltage measured in ST-FMR can contain contributions that are not directly related to SOTs, which affects the accuracy of the extracted torque efficiencies. This may contribute to the large variation of reported SOT efficiencies in literature. In this study, we investigate the damping-like torque efficiencies in CoFeB/Pt heterostructures as a function of Pt thickness. Conventional ST-FMR analysis yields an apparent sign reversal of the extracted efficiency at a Pt thickness of approximately 10 nm. By combining complementary measurement geometries and analysis approaches, we separate the torque-induced signal from additional voltage contributions that share the same angular dependence. Our results show that non-torque voltage contributions can produce an apparent sign reversal in conventional ST-FMR analysis, highlighting the need to distinguish SOT-induced signals from parasitic contributions and we show how to reliably determine the SOT efficiencies.
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BibTeX
@misc{berg2026sign,
title = {{Sign reversal of ST-FMR signals in CoFeB/Pt explained by contributions beyond spin-orbit torque}},
author = {Christian Berg and Ao Du and Durgesh Kumar and Sinan Shu and Sourabh Manna and Sachin Krishnia and Mathias Kläui},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.39749},
eprint = {2610.39749},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.39749},
}
RIS
TY - UNPB
TI - Sign reversal of ST-FMR signals in CoFeB/Pt explained by contributions beyond spin-orbit torque
AU - Christian Berg
AU - Ao Du
AU - Durgesh Kumar
AU - Sinan Shu
AU - Sourabh Manna
AU - Sachin Krishnia
AU - Mathias Kläui
PY - 2026
DA - 2026/10/29
PB - arXiv
DO - 10.48550/arxiv.2610.39749
UR - https://arxiv.org/abs/2610.39749
AB - Spin-orbit torques (SOT) provide an efficient route for electrical control of magnetization and is of central interest for low-power magnetic memory applications. Spin-torque ferromagnetic resonance (ST-FMR) is a widely used technique to quantify SOT efficiencies. However, the rectified voltage measured in ST-FMR can contain contributions that are not directly related to SOTs, which affects the accuracy of the extracted torque efficiencies. This may contribute to the large variation of reported SOT efficiencies in literature. In this study, we investigate the damping-like torque efficiencies in CoFeB/Pt heterostructures as a function of Pt thickness. Conventional ST-FMR analysis yields an apparent sign reversal of the extracted efficiency at a Pt thickness of approximately 10 nm. By combining complementary measurement geometries and analysis approaches, we separate the torque-induced signal from additional voltage contributions that share the same angular dependence. Our results show that non-torque voltage contributions can produce an apparent sign reversal in conventional ST-FMR analysis, highlighting the need to distinguish SOT-induced signals from parasitic contributions and we show how to reliably determine the SOT efficiencies.
ER -