We report on first-principles calculations of spin-transfer torque (STT) in epitaxial magnetic tunnel junctions (MTJs) based on ferrimagnetic tetragonal ${\mathrm{Mn}}_3\mathrm{Ga}$ electrodes, both as analyzer in a Fe/MgO stack, and also in an analogous stack with a second ${\mathrm{Mn}}_3\mathrm{Ga}$ electrode (instead of Fe) as polarizer. Solving the ballistic transport problem ($\mathrm{NEGF}+\mathrm{DFT}$) for the nonequilibrium spin density in a scattering region extended to over 7.6 nm into the ${\mathrm{Mn}}_3\mathrm{Ga}$ electrode, we find long-range spatial oscillations of the STT decaying on a length scale of a few tens of angstroms, both in the linear response regime and for finite bias. The oscillatory behavior of the STT in ${\mathrm{Mn}}_3\mathrm{Ga}$ is robust against variations in the stack geometry (e.g., the barrier thickness and the interface spacing) and the applied bias voltage, which may affect the phase and the amplitude of the spacial oscillation, but the high (carrier) frequency mode is only responsive to variations in the longitudinal lattice constant of ${\mathrm{Mn}}_3\mathrm{Ga}$ (for fixed in-plane geometry) without being commensurate with the lattice. Our interpretation of the long-range STT oscillations is based on the bulk electronic structure of ${\mathrm{Mn}}_3\mathrm{Ga}$, taking also into account the spin-filtering properties of the MgO barrier. Comparison to a fully ${\mathrm{Mn}}_3\mathrm{Ga}$-based stack shows similar STT oscillations, but a significant enhancement of both the TMR effect at the Fermi level and the STT at the interface, due to resonant tunneling for the mirror-symmetric junction with thinner barrier (three monoatomic layers). From the calculated energy dependence of the spin-polarized transmissions at 0 V, we anticipate asymmetric or symmetric TMR as a function of the applied bias voltage for the Fe-based and the all-${\mathrm{Mn}}_3\mathrm{Ga}$ stacks, respectively, which also both exhibit a sign change below $\pm 1\mathrm{V}$. In the latter, symmetric, case we expect a TMR peak at zero, which is larger for the thinner barriers because of a spin-polarized resonant tunneling contribution.

中文翻译：

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基于第一原理的基于Mn3Ga的铁磁隧道结中的自旋传递扭矩

我们报告基于铁磁四边形的外延磁性隧道结（MTJs）中自旋传递扭矩（STT）的第一性原理计算 ${锰}_3嘎$ 电极，既可以用作Fe / MgO堆栈中的分析仪，也可以用作具有第二个电极的类似堆栈中的分析仪 ${锰}_3嘎$电极（代替铁）作为极化器。解决弹道运输问题（$\mathrm{神经生长因子}+\mathrm{DFT}$）的散射区域中的非平衡自旋密度扩展到7.6 nm以上 ${锰}_3嘎$电极，我们发现STT的远距离空间振荡在线性响应范围和有限偏置中都在几十埃的长度尺度上衰减。STT在中的振荡行为${锰}_3嘎$ 对堆叠几何形状（例如，势垒厚度和界面间距）和施加的偏置电压的变化具有鲁棒性，这可能会影响空间振荡的相位和幅度，但是高（载波）频率模式仅对的纵向晶格常数的变化 ${锰}_3嘎$（用于固定的平面几何形状）而与晶格不相称。我们对远程STT振荡的解释是基于${锰}_3嘎$，还考虑了MgO势垒的自旋过滤特性。完全比较${锰}_3嘎$的堆叠显示出相似的STT振荡，但是由于具有更薄势垒（三个单原子层）的镜对称结的共振隧穿，费米能级的TMR效应和界面处的STT都得到了显着增强。根据计算得出的自旋极化传输在0 V时的能量依赖性，我们预计非对称或对称TMR随所施加的基于Fe的偏置电压和所有基于${锰}_3嘎$ 堆栈，分别在下面也都显示出符号变化 $\pm \mathrm{1个}\mathrm{伏特}$。在后者的对称情况下，我们期望TMR峰值为零，这对于较薄的势垒来说更大，这是因为自旋极化共振隧穿的影响。