Large enhancement of spin–orbit torques under a MHz modulation due to phonon

DOI：

10.1063/5.0174580

发表时间：

2023-12

期刊：

Applied Physics Letters

影响因子：

通讯作者：

中科院分区：

物理与天体物理2区

文献类型：

作者：

Han-tao Zhang;Qianwen Zhao;Baiqing Jiang;Yuan Wang;T. Xie;Kaihua Lou;ChaoChao Xia;C. Bi

自旋轨道力矩（SOTs）的发现为磁随机存取存储器（MRAM）提供了另一种写入方法，点燃了近年来自旋轨道电子学的发展。sot的定量表征高度依赖于sot驱动的铁磁共振（ST-FMR），其中调制的微波电流用于产生交流sot，调制频率通常小于100 kHz（传统锁相放大器的极限）。在这里，我们通过开发ST-FMR测量，在扩展的调制频率范围（高达MHz）中研究了典型SOT材料/铁磁体双层的SOT。值得注意的是，我们发现测量到的SOT在MHz范围内增加了约3倍，这是目前SOT理论无法解释的。我们将SOT的增强归因于声子-磁振子耦合带来的额外磁振子激励，这也反映在所获得的ST-FMR光谱中谐振场和线宽的微小变化上，这分别对应于有效磁化常数和阻尼常数的改变。结果表明，在声子-磁振子耦合的帮助下，SOT-MRAM的写入电流可能会减小。

The discovery of spin–orbit torques (SOTs) generated through the spin Hall or Rashba effects provides an alternative write approach for magnetic random-access memory (MRAM), igniting the development of spin orbitronics in recent years. Quantitative characterization of SOTs highly relies on the SOT-driven ferromagnetic resonance (ST-FMR), where a modulated microwave current is used to generate ac SOTs and the modulation frequency is usually less than 100 kHz (the limit of conventional lock-in amplifiers). Here, we have investigated the SOT of typical SOT material/ferromagnet bilayers in an extended modulation-frequency range, up to MHz, by developing the ST-FMR measurement. Remarkably, we found that the measured SOTs are enhanced about three times in the MHz range, which cannot be explained according to the present SOT theory. We attribute the enhancement of SOT to additional magnon excitations due to phonon–magnon coupling, which is also reflected in the slight changes of resonant field and linewidth in the acquired ST-FMR spectra, corresponding to the modifications of effective magnetization and damping constant, respectively. Our results indicate that the write current of SOT-MRAM may be reduced with the assistance of phonon–magnon coupling.

Large enhancement of spin–orbit torques under a MHz modulation due to phonon–magnon coupling

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