Realizing unipolar and bipolar intrinsic skyrmions in MXenes from high-fidelity first-principles calculations

Arnab Kabiraj & Santanu Mahapatra 

npj Computational Materials 9: 173 (2023); Published online: 25 September 2023

编辑概述：存在斯格明子MXenes的高通量计算

斯格明子是拓扑保护的非共线磁性模式，自旋排列成漩涡状，表现为纳米级准粒子，可以通过自旋极化电流和磁场进行操纵。具有稳定斯格明子的材料可用于制造超低功耗的微观尺度信息存储和处理设备。例如，逻辑1和0可以由斯格明子的存在和缺失来表示。斯格明子通常通过在重金属异质层界面诱导大的Dzyaloshinskii-Moriya相互作用（DMI）来实现。实验表明，一些铁磁/重金属异质结构，如Fe/Ir (111)、 Ir/Fe/Co/Pt、Pt/Co/MgO等，可以产生较大的DMI。这是因为，表面的反演对称性丧失以及由重金属和Rashba效应导致的强自旋-轨道耦合，从而引出较大的DMI。理论也预测在Co表面沉积的二维材料如石墨烯和hBN会产生斯格明子态。然而，这些异质结的界面缺陷以及层间堆叠顺序对DMI的提升不利。因此，设计具有反演不对称性的单层材料，以创造有利于稳定斯格明子的条件，是非常有价值的。在本文中，来自印度科学院班加罗尔电子系统工程系的Santanu Mahapatra教授团队，结合基于高保真交换-关联泛函的第一性原理计算以及微磁和蒙特卡罗模拟，探索了含有单层磁性金属的MXene特定子类中斯格明子的存在。作者开发了一个全自动的高通量计算工作流，严格扫描了大约3000种材料的大空间，最终得到了91种有望形成稳定斯格明子的材料。此外，作者还发现了一些材料能够在室温下无需任何外部磁场即可形成垂直于平面的斯格明子，这对于设计与当前技术兼容的基于斯格明子的设备很有价值。本工作可能加速并有助于斯格明子基自旋电子学的工程化。

Editorial Summary: A high-throughput calculation on MXenes with intrinsic Skyrmions

Skyrmions, topologically protected noncollinear magnetic patterns with spins arranged in a whirl, behave as nanometer-sized quasiparticles and can be manipulated using spin-polarized currents and magnetic fields. Materials with stable skyrmions can be used to fabricate devices that can store and process information at microscopic length scales with ultra-low power consumption. For example, logic 1 and 0 can be represented by the presence and absence of the skyrmion. Skyrmions are commonly realized by inducing large Dzyaloshinskii–Moriya interaction (DMI) in the interface of heavy metal heterolayers. In experiments, ferromagnet/heavy metal heterostructures such as Fe/Ir(111), Ir/Fe/Co/Pt, Pt/Co/MgO were synthesized to generate large DMIs. This can be understood by the loss of inversion symmetry at the surface and large spin-orbit coupling due to the presence of heavy metals and the Rashba effect, which led to large Dzyaloshinskii–Moriya interactions (DMI).  Besides, two-dimensional (2D) materials such as graphene and hBN on Co surfaces has been predicted to result in skyrmion states. However, the DMI is adversely affected by defects at the interface as well as the stacking order of the layers. Designing a single layer of material with inversion asymmetry that creates conditions favorable for stabilizing skyrmions is, therefore, highly desirable. In this work, a group led by Prof. Santanu Mahapatra from the Department of Electronic Systems Engineering, Indian Institute of Science (IISc) Bangalore, combined high-fidelity exchange-correlation functional-based first-principles calculations with micromagnetic and Monte Carlo (MC) simulations, to explore a specific subclass of MXenes containing a single magnetic metal layer for the presence of skyrmions. A fully automated high-throughput computational workflow was developed to rigorously scan a large space of around 3000 materials. The authors ended up with 91 promising materials capable of hosting stable skyrmions. They also found a few materials capable of hosting out-of-plane skyrmions at room temperature without any external magnetic field, which can be useful for designing skyrmion-based devices compatible with the current technology. This work could accelerate and aid in the engineering of skyrmion-based spintronics.