报告：First-principles study of Dzyaloshinskii-Moriya Interaction
报告人：杨洪新（中国科学院磁性材料与器件重点实验室，宁波材料技术与工程研究所）
时间： 2018年6月14日（星期四） 上午9：30
地点： 唐仲英楼A313
Abstract:
The Dzyaloshinskii-Moriya Interaction (DMI) between spins induced by spin-orbit coupling (SOC) in magnetic materials lacking inversion symmetry and in particular at the interface between ferromagnetic (FM) and heavy nonmagnetic (NM) metals has become recently a subject of tremendous interest for both scientists and engineers. This is because the DMI is recognized to play the most prominent role for creating topologically non-trivial textures called magnetic skyrmions which are very attractive for ultra-dense information storage and spintronic devices. Furthermore, DMI plays an essential role for fast domain wall (DW) dynamics driven by spin-orbit torques. It has been shown that the DW velocity strongly depends on the relative parameters of exchange coupling, magnetic anisotropy and the DMI. Thus, much attention has been paid on searching efficient material combinations giving rise to large DMI values at FM/NM interfaces.
The study of DMI at Pt/Co interfaces [1] has unveiled the main features and microscopic mechanisms of DMI in NM/FM bilayers. We found that the large anticlockwise (ACW) DMI of the Pt/Co bilayers has a predominant contribution from pair couplings between the spins of the interfacial Co layer. This DMI between the interface Co spins is directly related to the change of the SOC energy in the interface Pt atoms, demonstrating the picture of Fert-Levy type interfacial DMI from first-principles.
Based on the understanding of the DMI mechanism at FM/NM interfaces [1], we propose several approaches to control the DMI in ultrathin magnetic films and enhance its amplitude. First, the DMI can be enlarged via multilayer stacking of FM and NM metals possessing the required DMI chiralities in corresponding FM/NM bilayers. Next approach is adding an oxidized capping layer, such as MgO, on top of a Pt/Co bilaye. We show that the DMI in Pt/Co/MgO is much larger, about 1.6 times, compared to that in Pt/Co bilayers for all the Co thicknesses considered. [2] Moreover, we explore the possibility of electric field control of DMI in FM/NM/Oxide structures, which opens a route towards an efficient way for controlling skyrmions. [3] Finally, we report the Rashba effect induced interfacial Dzyaloshinskii-Moriya Interaction (DMI) at graphene /FM interfaces [4].
[1] H. X. Yang, et al. Physical Review Letters 115, 267210 (2015).
[2] O. Boulle, H. X. Yang et al. Nature Nanotech. 11, 449-454 (2016)
[3] H Yang, O Boulle, V Cros, A Fert, M Chshiev, arXiv preprint arXiv:1603.01847
[4] H. Yang, G. Chen, A. A.C. Cotta, A. T. N'Diaye, S. A. Nikolaev, E. A. Soares, W. A. A. Macedo, A. K. Schmid, A. Fert, M. Chshiev, Nature Materials（2018）doi:10.1038/s41563-018-0079-4
