Two Strategies to Measure Spin-Orbit-Torque Efficiency Acting on the Insulating Magnet Li0.5Al0.7Fe1.8O4
Abstract
For insulating magnets, widely-used electrically-based techniques to measure spin-orbit-torque efficiency can suffer from poor signal-to-noise ratios and unwanted artifacts, while optical measurements based on conventional magneto-optical Kerr effect (MOKE) imaging often lack sufficient sensitivity. Here we analyze two strategies for measuring the spin-torque efficiency acting on an insulating magnet, focusing on the torque from Pt acting on thin films of the low-damping magnet lithium aluminum ferrite (LAFO). First, lateral + longitudinal spin-torque ferromagnetic resonance (ST-FMR) allows separation of the spin-torque signal from artifacts due to spin-pumping and resonant heating. With this technique, we measure a spin-torque efficiency ξST−FMRDL∼ 0.07, comparable to but a bit less than for Pt acting on metallic ferromagnets. Second, we attempted optical measurements of spin-orbit-torque-induced magnetic deflection using Sagnac interferometry. We find that Sagnac interferometry provides sufficient sensitivity to measure signals from 14.4 nm LAFO thin films, but the inferred torque efficiency is much weaker than the result from lateral + longitudinal ST-FMR. We speculate that there may be another contribution to the Sagnac signal other than current-induced magnetic deflection, perhaps an out-of-plane component of itinerant electron spins. This becomes relevant for insulating magnets in which the magneto-optic coupling coefficient is very weak.
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BibTeX
@misc{smedley2026strategies,
title = {{Two Strategies to Measure Spin-Orbit-Torque Efficiency Acting on the Insulating Magnet Li$_0.5$Al$_0.7$Fe$_1.8$O$_4$}},
author = {Orion Smedley and Thow Min Jerald Cham and Daisy O'Mahoney and Sanyum Channa and Xin Yu Zheng and Anna Janni and Lauren J. Riddiford and Yuhan Liang and Bozo Vareskic and Zbigniew Galazka and Yunqiu Kelly Luo and Yuri Suzuki and Daniel C. Ralph},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.15474},
eprint = {2609.15474},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.15474},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Two Strategies to Measure Spin-Orbit-Torque Efficiency Acting on the Insulating Magnet Li_0.5Al_0.7Fe_1.8O_4
AU - Orion Smedley
AU - Thow Min Jerald Cham
AU - Daisy O'Mahoney
AU - Sanyum Channa
AU - Xin Yu Zheng
AU - Anna Janni
AU - Lauren J. Riddiford
AU - Yuhan Liang
AU - Bozo Vareskic
AU - Zbigniew Galazka
AU - Yunqiu Kelly Luo
AU - Yuri Suzuki
AU - Daniel C. Ralph
PY - 2026
DA - 2026/09/14
PB - arXiv
DO - 10.48550/arxiv.2609.15474
UR - https://arxiv.org/abs/2609.15474
AB - For insulating magnets, widely-used electrically-based techniques to measure spin-orbit-torque efficiency can suffer from poor signal-to-noise ratios and unwanted artifacts, while optical measurements based on conventional magneto-optical Kerr effect (MOKE) imaging often lack sufficient sensitivity. Here we analyze two strategies for measuring the spin-torque efficiency acting on an insulating magnet, focusing on the torque from Pt acting on thin films of the low-damping magnet lithium aluminum ferrite (LAFO). First, lateral + longitudinal spin-torque ferromagnetic resonance (ST-FMR) allows separation of the spin-torque signal from artifacts due to spin-pumping and resonant heating. With this technique, we measure a spin-torque efficiency ξ^ST−FMR_DL∼ 0.07, comparable to but a bit less than for Pt acting on metallic ferromagnets. Second, we attempted optical measurements of spin-orbit-torque-induced magnetic deflection using Sagnac interferometry. We find that Sagnac interferometry provides sufficient sensitivity to measure signals from 14.4 nm LAFO thin films, but the inferred torque efficiency is much weaker than the result from lateral + longitudinal ST-FMR. We speculate that there may be another contribution to the Sagnac signal other than current-induced magnetic deflection, perhaps an out-of-plane component of itinerant electron spins. This becomes relevant for insulating magnets in which the magneto-optic coupling coefficient is very weak.
ER -