Highly efficient spin-orbit torque in Pt/Co/Ir multilayers with antiferromagnetic interlayer exchange coupling
Highly efficient spin-orbit torque in Pt/Co/Ir multilayers with antiferromagnetic interlayer exchange coupling
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DOI：
10.1103/physrevb.101.014404
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发表时间：
2020-01-03
影响因子：
3.7
通讯作者：
Hayashi, Masamitsu
中科院分区：
文献类型：
--
作者：
Ishikuro, Yuto;Kawaguchi, Masashi;Hayashi, Masamitsu
我们研究了具有三个重复单元结构的 Pt/Co/Ir 多层膜中的自旋轨道扭矩 (SOT)。由于系统表现出不同 Ir 层厚度的振荡层间交换耦合，我们比较了 Co 层铁磁和反铁磁耦合时薄膜的 SOT。 SOT 使用异常霍尔电阻磁滞回线的电流感应位移进行评估。相对较厚的 Pt 层用作多层的种子层，用于通过自旋霍尔效应产生自旋电流。在没有反铁磁耦合的情况下，SOT 对于所施加的电流密度是恒定的，并且相应的自旋扭矩效率（即有效自旋霍尔角）类似于 0.09，与之前的报告一致。相反，对于具有反铁磁耦合的薄膜，SOT 随着施加的电流密度而增加并最终饱和。饱和时的 SOT 比没有反铁磁耦合时大大约 15 倍。如果我们假设净总磁化强度由于反铁磁耦合而减少了 3 倍，则自旋扭矩效率大约会增加 5 倍。基于 Landau-Lifshitz-Gilbert 方程的模型计算表明，反铁磁耦合的存在可以增加 SOT，但增强程度有限，在这种情况下，增强程度为 1.2-1.4 倍。因此，我们认为 SOT 还存在其他来源，可能是在界面处，这可能解释了未补偿的合成反铁磁体多层中的高效 SOT。
We have studied the spin-orbit torque (SOT) in Pt/Co/Ir multilayers with three repeats of the unit structure. As the system exhibits oscillatory interlayer exchange coupling with varying Ir layer thickness, we compare the SOT of films when the Co layers are coupled ferromagnetically and antiferromagnetically. SOT is evaluated using current-induced shift of the anomalous Hall resistance hysteresis loops. A relatively thick Pt layer, serving as a seed layer to the multilayer, is used to generate spin current via the spin Hall effect. In the absence of antiferromagnetic coupling, the SOT is constant against the applied current density and the corresponding spin torque efficiency (i.e., the effective spin Hall angle) is similar to 0.09, in agreement with previous reports. In contrast, for films with antiferromagnetic coupling, the SOT increases with the applied current density and eventually saturates. The SOT at saturation is a factor of similar to 15 larger than that without the antiferromagnetic coupling. The spin torque efficiency is approximately five times larger if we assume the net total magnetization is reduced by a factor of 3 due to the antiferromagnetic coupling. Model calculations based on the Landau-Lifshitz-Gilbert equation show that the presence of antiferromagnetic coupling can increase the SOT but the degree of enhancement is limited, in this case, to a factor of 1.2-1.4. We thus consider there are other sources of SOT, possibly at the interfaces, which may account for the highly efficient SOT in the uncompensated synthetic antiferromagnet multilayers.