Oxygen incorporation has been reported to increase the current-induced spin-orbit torque in ferromagnetic heterostructures, but the underlying mechanism is still under active debate. Here, we report on an in-situ study of the oxygen exposure effect on spin-orbit torque in Pt/Co bilayers via controlled oxygen exposure, Co and Mg deposition, and electrical measurements in ultrahigh vacuum. We show that the oxygen exposure on Pt/Co indeed leads to an increase of spin-orbit torque, but the enhancement is not as large as those reported previously. Similar enhancement of spin-orbit torque is also observed after the deposition of an MgO capping layer. The results of ab initio calculations on the Rashba splitting of Pt/Co and Pt/Co/O suggest that the enhancement is due to enhanced Rashba-Edelstein effect by surface-adsorbed oxygen. Our findings shed some light on the varying roles of oxygen in modifying the spin torque efficiency reported previously.
Robust Gapless Surface State against Surface Magnetic Impurities on (Bi$_{0.5}$Sb$_{0.5}$)$_2$Te$_3$ Evidenced by In Situ Magnetotransport Measurements
尽管进行了大量的实验和理论研究，但表面磁性杂质对拓扑绝缘体（TI）拓扑表面态的影响这一重要问题仍未得到解决。我们阐明的（Bi $_{0.5}$ Sb $_{0.5}$）$_{2}$ Te $_{3}$：Cr吸附原子的外延薄膜上的影响是增量沉积到TI上的在低温下保持在真空中，和\textit{in situ}的磁导率和霍尔效应测量进行在每个增量与静电门控。在实验确定的表面传输制度，测得的最小电子密度显示出非单调的演变与铬密度（$n_{\mathrm{Cr}}$）：它首先增加，然后减少与$n_{\mathrm{Cr}}$。这种不寻常的行为归因于Cr作为离子化杂质和电子供体的双重作用，具有分别在低和高$n_{\mathrm{Cr}}$下增强和降低表面态中的电子不均匀性的竞争效应。不同的$n_{\mathrm{Cr}}$上的一个和相同的样品，这产生了明确的证据表明，弱的反局域化效应持续存在，表面状态保持无间隙的最高$n_{\mathrm{Cr}}$，相反的预期，沉积的Cr应该打破时间反演对称性，并诱导在狄拉克点的间隙开口。
Helium Ion Microscopy for Reduced Spin Orbit Torque Switching Currents
自旋轨道转矩驱动开关是一种有利的方式来操纵纳米磁性物体的存储器和无线通信设备。从一种磁状态切换到另一种磁状态所需的临界电流取决于所用材料的几何形状和固有特性，这些特性很难局部控制。在这里，我们展示了如何聚焦氦离子束照射可以调制局部磁各向异性的Co薄膜在微观尺度上。使用异常霍尔效应的实时原位表征显示了辐射下的磁各向异性的数量级减少，并使用此，多电平开关被证明。其结果是，自旋开关电流密度，低至800 kA cm $^{-2}$，可以实现在膜的预定区域，而不需要光刻。空间上改变临界电流的能力不仅对存储元件有影响，而且对神经形态和概率计算也有影响。
