Enhancement of spin-orbit torque efficiency by tailoring interfacial spin-orbit coupling in Pt-based magnetic multilayers

We study inserting Co layer thickness-dependent spin transport and spin-orbit torques (SOTs) in the Pt/Co/Py trilayers by spin-torque ferromagnetic resonance. The interfacial perpendicular magnetic anisotropy (IPMA) energy density ($K_{\rm s}= 2.7 $ erg/cm$^{2}$, 1 erg = 10$^{-7}$ J), which is dominated by interfacial spin-orbit coupling (ISOC) in the Pt/Co interface, total effective spin-mixing conductance $(G_{\mathrm{eff,tot}}^{\mathrm{\uparrow \downarrow }}=\mathrm{0.42\times }{10}^{15} \mathrm{\Omega }^{-1}\cdot\mathrm{m}^{-2}$) and two-magnon scattering ($\beta_{\mathrm{TMS}}= 0.46 {\mathrm{nm}}^{2}$) are first characterized, and the damping-like torque ($\xi_{\mathrm{DL}}= 0.103$) and field-like torque ($\xi _{\mathrm{FL}}=-0.017$) efficiencies are also calculated quantitatively by varying the thickness of the inserting Co layer. The significant enhancement of $\xi_{\mathrm{DL}}$ and $\xi_{\mathrm{FL}}$ in Pt/Co/Py than Pt/Py bilayer system originates from the interfacial Rashba-Edelstein effect due to the strong ISOC between Co-3d and Pt-5d orbitals at the Pt/Co interface. Additionally, we find a considerable out-of-plane spin polarization SOT, which is ascribed to the spin anomalous Hall effect and possible spin precession effect due to IPMA-induced perpendicular magnetization at the Pt/Co interface. Our results demonstrate that the ISOC of the Pt/Co interface plays a vital role in spin transport and SOTs-generation. Our finds offer an alternative approach to improve the conventional SOTs efficiencies and generate unconventional SOTs with out-of-plane spin polarization to develop low power Pt-based spintronic via tailoring the Pt/FM interface.     

垂直点接触自旋霍尔纳米振荡器中自旋波动力学的微磁学模拟

基于微磁学模拟的方法，对垂直点接触自旋霍尔纳米振荡器(VNC-SHNO)中自旋波的激发和其非线性动力行为随电流、磁场及角度的依赖关系进行了详细的数值模拟研究.首先研究了纳米振荡器的频谱特性随激发电流的变化的关系，发现在低电流下，其频谱在远低于铁磁共振频率f_FMR处出现一个自旋相干性很好的振荡峰f₁以及几个高阶谐波峰，且其频率随电流增加表现出明显的红移；而在高电流下，其频谱除了出现低频f₁峰以外，在接近f_FMR处还出现了一个高频峰f₂，但其频率几乎不随激发电流变化.其次，通过振荡模式的功率谱的空间分布图，发现f₁是局域在点接触边界的一类非线性“子弹”型自旋孤波，而f₂是分布在局域模f₁外围的一类准线性传播型自旋波.最后，还细致研究了外加磁场强度及外加磁场面外角度对自旋霍尔纳米振荡器中这两类自旋波的激发和调控规律，为下一步实验研究该器件的非线性动力特性及其在非线性逻辑计算中的应用提供了理论基础.