论文标题

Spintronics符合非绝热分子动力学:由于电子开放量子系统而导致的非共线性磁性旋转扭矩和阻尼

Spintronics meets nonadiabatic molecular dynamics: Geometric spin torque and damping on noncollinear classical magnetism due to electronic open quantum system

论文作者

Bajpai, Utkarsh, Nikolic, Branislav K.

论文摘要

我们分析了一个量子古典混合体系统,该系统稳定地进攻缓慢的经典局部磁矩,形成头对头域壁,并嵌入了快速非平衡电子的开放量子系统中。电子位于连接到宏观储层的金属线中。该模型捕获了Spintronics中动态非共线性和非稳态磁纹理的本质,同时使获得了电子系统的确切时间依赖性的非平衡密度矩阵成为可能,并将其分为四个贡献。费米表面的贡献在矩上产生耗散性(或在旋转术语中类似阻尼状的旋转术语),而两个费米海上的贡献之一产生了在绝热状态中占主导地位的几何扭矩。当减少与储层的耦合时,几何扭矩是唯一的非零贡献。在局部,它具有非隔离性(或旋转术语中的场状)和类似阻尼的组件,但后者的总和为零,它们在非绝热分子动力学中充当了几何磁力和电摩擦力的对应物。基于Landau-lifshitz-gilbert方程的磁化动力学的广泛使用的微磁化动力学建模不存在这种非依赖性的几何扭矩,而原子化动力学的旋转动力学建模,而先前对费米表面型扭矩的分析已严重低估了其大小。

We analyze a quantum-classical hybrid system of steadily precessing slow classical localized magnetic moments, forming a head-to-head domain wall, embedded into an open quantum system of fast nonequilibrium electrons. The electrons reside within a metallic wire connected to macroscopic reservoirs. The model captures the essence of dynamical noncollinear and noncoplanar magnetic textures in spintronics, while making it possible to obtain the exact time-dependent nonequilibrium density matrix of electronic system and split it into four contributions. The Fermi surface contribution generates dissipative (or damping-like in spintronics terminology) spin torque on the moments, and one of the two Fermi sea contributions generates geometric torque dominating in the adiabatic regime. When the coupling to the reservoirs is reduced, the geometric torque is the only nonzero contribution. Locally it has both nondissipative (or field-like in spintronics terminology) and damping-like components, but with the sum of latter being zero, which act as the counterparts of geometric magnetism force and electronic friction in nonadiabatic molecular dynamics. Such current-independent geometric torque is absent from widely used micromagnetics or atomistic spin dynamics modeling of magnetization dynamics based on the Landau-Lifshitz-Gilbert equation, where previous analysis of Fermi surface-type torque has severely underestimated its magnitude.

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