The spin-transfer-torque-driven (STT-driven) dynamics of a domain wall in an easy-axis rare-earth transition-metal ferrimagnet is investigated theoretically and numerically in the vicinity of the angular momentum compensation point $T_A$, where the net spin density vanishes. The particular focus is given on the unusual interaction of the antiferromagnetic dynamics of a ferrimagnetic domain wall and the adiabatic component of STT, which is absent in antiferromagnets but exists in the ferrimagnets due to the dominant coupling of conduction electrons to transition-metal spins. Specifically, we first show that the STT-induced domain-wall velocity changes its sign across $T_A$ due to the sign change of the net spin density, giving rise to a phenomenon unique to ferrimagnets that can be used to characterize $T_A$ electrically. It is also shown that the frequency of the STT-induced domain-wall precession exhibits its maximum at $T_A$ and it can approach the spin-wave gap at sufficiently high currents. Lastly, we report a numerical observation that, as the current density increases, the domain-wall velocity starts to deviate from the linear-response result, calling for a more comprehensive theory for the domain-wall dynamics in ferrimagnets driven by a strong current.

中文翻译：

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由自旋转移力矩驱动的亚铁磁体畴壁动力学

在角动量补偿点 $T_A$ 附近，从理论上和数值上研究了易轴稀土过渡金属亚铁磁体中畴壁的自旋转移扭矩驱动（STT 驱动）动力学，其中净自旋密度消失。特别关注亚铁磁畴壁的反铁磁动力学与 STT 的绝热成分的不寻常相互作用，这在反铁磁体中不存在，但由于传导电子与过渡金属自旋的主要耦合而存在于亚铁磁体中。具体来说，我们首先表明，由于净自旋密度的符号变化，STT 引起的畴壁速度在 $T_A$ 上改变了其符号，从而产生了亚铁磁体特有的现象，可用于表征 $T_A$ . 还表明 STT 引起的畴壁进动的频率在 $T_A$ 处显示出最大值，并且它可以在足够高的电流下接近自旋波隙。最后，我们报告了一个数值观察结果，随着电流密度的增加，畴壁速度开始偏离线性响应结果，这需要一个更全面的强电流驱动亚铁磁体畴壁动力学理论。