Electric field effect on magnetic interactions in ultrathin transition-metal films

自旋电子学目前面临的一个挑战是如何控制磁性材料中的局部自旋结构，如手性畴壁、skyrmions或反skyrmions，这是迈向应用的关键一步。电场的使用是有吸引力的，因为它提供了一种以低能源成本局部改变磁性的方法。因此，在铁磁半导体、多铁性材料和磁性金属等材料中，利用电场控制磁性的研究已经取得了很大的进展。在金属中，焦点主要集中在电场诱导磁晶各向异性的变化上。在这个项目中，我们将使用多尺度方法结合密度泛函理论（DFT）和原子自旋动力学模拟来探索电场操纵过渡金属界面局部自旋结构的可能性。我们的重点将是在具有铁磁或反铁磁交换和显著的Dzyaloshinskii-Moriya相互作用（DMI）的表面上的超薄过渡金属薄膜，其表现出手性畴壁或磁skyrmions。基于DFT，我们将计算交换和DMI的电场依赖关系以及磁晶各向异性能量。在这些系统中，电场引起的磁相互作用的变化可能允许写入和/或删除这种局域自旋结构。我们将通过原子自旋动力学来探索这种可能性，利用从DFT计算中得到的参数化的磁相互作用，包括电场的影响。表面电场的局部变化，例如由于扫描隧道显微镜的尖端，可以包括在这些模拟中。应用测地线微推弹性带（GNEB）方法，获得了skyrmions或反skyrmions等局域自旋结构坍塌或产生的能量势垒。采用谐波过渡态理论计算了寿命。

A current challenge in the field of spintronics is the manipulation of localized spin structures such as chiral domain walls, skyrmions, or antiskyrmions in magnetic materials, which is a crucial step towards applications. The use of electric fields is attractive as it provides a means to change magnetic properties locally and at low energy cost. Therefore, there has been a large research effort to control magnetism by electric fields in materials such as ferromagnetic semiconductors, multiferroics and magnetic metals. In metals, the focus has been mainly on the electric-field induced change of the magnetocrystalline anisotropy. In this project we will use a multiscale approach combining density functional theory (DFT) and atomistic spin dynamics simulations to explore the possibility of manipulating localized spin structures at transition-metal interfaces by electric fields. Our focus will be ultrathin transition-metal films at surfaces with ferro- or antiferromagnetic exchange and significant Dzyaloshinskii-Moriya interaction (DMI), which exhibit chiral domain walls or magnetic skyrmions. Based on DFT we will calculate the electric field dependence of the exchange and the DMI as well as the magnetocrystalline anisotropy energy. The electric field induced changes of the magnetic interactions in these systems may allow to write and/or to delete such localized spin structures. We will explore this possibility by atomistic spin dynamics using the magnetic interactions as parametrized from our DFT calculations including the effect of the electric field. The local variation of the electric field on the surface e.g. due to the tip of a scanning tunneling microscope can be included in these simulations. The energy barriers for the collapse or creation of localized spin structures such as skyrmions or antiskyrmions will be obtained by applying the geodesic nudged elastic band (GNEB) method. Harmonic transition-state theory is used to calculate the lifetimes.