垂直极化电流驱动的反铁磁畴壁动力学研究

The dynamics of magnetic domain walls is of great importance for both the fundamental magnetic theory and the potential application of magnetic materials. Therefore, domain wall motion is a research focus in magnetics. The manipulation of magnetic domain wall motion has been extensively studied in the past few years while relatively few studies focused on the antiferromagnetic domain walls. There are still lots of unknowns for the domain walls in antiferromagnetic materials. Most research on the dynamics of antiferromagnetic domain walls is the theoretical study based on a one-dimensional domain wall model in the framework of the phenomenological equations, sometimes with the help of numerical simulations as well. It is known that an antiferromagnetic domain wall can be moved by an in-plane spin-polarized current or spin waves. In this project, we will use the classical spin model to study the dynamics of antiferromagnetic domain walls driven by a spin-polarized current perpendicular to the plane. We have the following research tasks in this project: (1) to determine whether the pure rotational mode exists for an antiferromagnetic domain wall; (2) to investigate the contributions of the two spin-transfer torques (i.e., a Slonczewski torque and a fieldlike torque) on the dynamics of antiferromagnetic domain walls; (3) to explore the influence of the antisymmetric exchange interaction (Dzyaloshinskii-Moriya interaction) on the dynamics of antiferromagnetic domain walls. Moreover, we will try to obtain the phenomenological equations of antiferromagnetic materials in the presence of Dzyaloshinskii-Moriya interaction based on the classical spin model, and thus to establish the relation between classical spin model and the phenomenological theory. Therefore, a successful evaluation of this project will be a great help for the application of antiferromagnetic materials as well as the understanding of the antiferromagnetic domain wall dynamics.

磁性畴壁动力学的研究对基础理论和磁性材料的应用都有着重要的意义， 也是当代磁学界研究的热点问题之一。以前人们主要集中研究了铁磁畴壁运动，但对反铁磁畴壁运动的研究较少。至今为止，反铁磁畴壁运动的基本规律尚不完全清楚。当前研究反铁磁畴壁动力学的方法主要是通过唯象理论对一维畴壁进行理论分析，有时也借助于数值模拟。对反铁磁的研究主要集中在面内自旋极化电流、自旋波诱发的畴壁动力学上。本课题拟基于经典自旋模型对垂直极化电流驱动下的反铁磁畴壁动力学进行研究， 具体的研究任务为：（1）确定反铁磁畴壁是否存在纯翻转的运动模式；（2）讨论两种自旋转移矩对反铁磁畴壁运动的贡献；（3）研究反对称交换作用对畴壁运动的影响。此外，我们将尝试得到在考虑反对称交换作用下的唯象反铁磁动力学方程，进而建立经典自旋模型和唯象理论之间的联系。这些研究将有助于加深对反铁磁畴壁动力学的认识，对反铁磁的具体应用也会起到促进作用。

与铁磁材料相比，反铁磁材料具有工作频率高以及偶极相互影响较小等优点。本项目针对反铁磁体系的动力学特点，通过对比反铁磁体系与铁磁体系的差异，预测了反铁磁体系中可能存在磁子的颤动现象(Zitterbewegung)。我们研究了旋转磁场以及极化电流驱动的反铁磁畴壁的动力学，发现: （1）在DMI存在时旋转磁场可以有效的驱动反铁磁畴壁；（2）反铁磁畴壁在垂直极化电流驱动下可以出现纯翻转的模式，当电流密度较大时可以诱发螺旋波。此外，在项目执行期间我们开发了支持GPU加速的微磁学软件包JuMag。