测量作用于绝缘磁体Li$_{0.5}$Al$_{0.7}$Fe$_{1.8}$O$_4$上的自旋轨道转矩效率的两种策略
Two Strategies to Measure Spin-Orbit-Torque Efficiency Acting on the Insulating Magnet Li$_{0.5}$Al$_{0.7}$Fe$_{1.8}$O$_4$
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- Cornell University（康奈尔大学）
- Stanford University（斯坦福大学）
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中文总结 AI 辅助
本文针对绝缘磁体LAFO，提出横向+纵向ST-FMR和Sagnac干涉两种测量自旋轨道转矩效率的策略，前者测得效率约0.07，后者灵敏度足够但结果偏弱，可能源于额外自旋贡献。
中文摘要 AI 辅助
对于绝缘磁体，广泛使用的基于电学的方法来测量自旋轨道转矩效率可能遭受较差的信噪比和不期望的伪影，而基于传统磁光克尔效应（MOKE）成像的光学测量通常缺乏足够的灵敏度。在此，我们分析了两种测量作用于绝缘磁体上的自旋转矩效率的策略，重点关注Pt作用于低阻尼磁体锂铝铁氧体（LAFO）薄膜上的转矩。首先，横向+纵向自旋转矩铁磁共振（ST-FMR）允许将自旋转矩信号与自旋泵浦和共振加热引起的伪影分离。利用该技术，我们测量得到自旋转矩效率$\xi^\text{ST-FMR}_\text{DL}\sim\\ 0.07$，与Pt作用于金属铁磁体上的效率相当但略低。其次，我们尝试使用Sagnac干涉仪对自旋轨道转矩引起的磁偏转进行光学测量。我们发现Sagnac干涉测量法提供了足够的灵敏度来测量来自14.4 nm LAFO薄膜的信号，但推断的转矩效率远弱于横向+纵向ST-FMR的结果。我们推测Sagnac信号中可能存在除电流引起的磁偏转之外的其他贡献，或许是巡回电子自旋的面外分量。这对于磁光耦合系数非常弱的绝缘磁体变得相关。
英文摘要
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 $ξ^\text{ST-FMR}_\text{DL}\sim\ 0.07$, 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.
