Spin-orbit torque generation in NiFe/IrO2 bilayers
Spin-orbit torque generation in NiFe/IrO2 bilayers
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DOI：
10.1103/physrevb.102.134432
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发表时间：
2020-10
影响因子：
3.7
通讯作者：
K. Ueda;Naoki Moriuchi;Kenta Fukushima;T. Kida;M. Hagiwara;J. Matsuno
中科院分区：
文献类型：
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作者：
K. Ueda;Naoki Moriuchi;Kenta Fukushima;T. Kida;M. Hagiwara;J. Matsuno
$5d$过渡金属氧化物具有独特的电子结构，由强自旋轨道耦合主导，因此它们可以成为探索自旋电流物理的有趣平台。本文报道了一种导电的$5d$氧化铱$\ mathm {Ir}{\ mathm {O}}_{2}$在室温下产生自旋轨道转矩（SOT）的方法。通过测量${\ mathm {Ni}}_{81}}{\ mathm {Fe}}_{19}/\ mathm {Ir}{\ mathm {O}}_{2}$两层的二次谐波霍尔电阻，我们发现了类阻尼型和类场型SOTs。前者比后者更大，更容易控制磁化。我们还观察到，类阻尼SOT效率对$\ mathm {Ir}{\ mathm {O}}_{2}$厚度有显著的依赖性，这可以用基于体自旋霍尔效应的漂移-扩散模型很好地描述。我们推导出有效自旋霍尔角为+0.093 \ifmmode\pm\else\textpm\fi{} 0.003，自旋扩散长度为1.7 \ifmmode\pm\else\textpm\fi{} 0.2 nm。通过与对照样品Pt和Ir的比较，我们发现$\mathrm{Ir}{\mathrm{O}}_{2}$的有效自旋霍尔角与Pt相当，是Ir的7倍。与类阻尼SOT相比，类场SOT效率有一个负号，对厚度没有明显的依赖性。这表明类似字段的SOT可能源于接口。这些实验结果表明，$5d$过渡金属氧化物的电子结构的独特性对于高效的电荷到自旋电流转换至关重要。
The $5d$ transition-metal oxides have a unique electronic structure dominated by strong spin-orbit coupling and hence they can be an intriguing platform to explore spin-current physics. Here, we report on room-temperature generation of spin-orbit torque (SOT) from a conductive $5d$ iridium oxide, $\mathrm{Ir}{\mathrm{O}}_{2}$. By measuring second-harmonic Hall resistance of ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}/\mathrm{Ir}{\mathrm{O}}_{2}$ bilayers, we find both dampinglike and fieldlike SOTs. The former is larger than the latter, enabling easier control of magnetization. We also observe that the dampinglike SOT efficiency has a significant dependence on $\mathrm{Ir}{\mathrm{O}}_{2}$ thickness, which is well described by the drift-diffusion model based on the bulk spin Hall effect. We deduce the effective spin Hall angle of +0.093 \ifmmode\pm\else\textpm\fi{} 0.003 and the spin-diffusion length of 1.7 \ifmmode\pm\else\textpm\fi{} 0.2 nm. By comparison with control samples Pt and Ir, we show that the effective spin Hall angle of $\mathrm{Ir}{\mathrm{O}}_{2}$ is comparable to that of Pt and seven times higher than that of Ir. The fieldlike SOT efficiency has a negative sign without appreciable dependence on the thickness, in contrast to the dampinglike SOT. This suggests that the fieldlike SOT likely stems from the interface. These experimental findings suggest that the uniqueness of the electronic structure of $5d$ transition-metal oxides is crucial for highly efficient charge to spin-current conversion.