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。

Fig. 1 Anatomy of the MXenes.

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。

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。作者的工作可以加速并有助于斯格明子基自旋电子学的工程化。该文近期发布于npj Computational Materials9: 173 (2023)。

Editorial Summary

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. 

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. This article was recently published in npj Computational Materials 9: 173 (2023).

原文Abstract及其翻译

Realizing unipolar and bipolar intrinsic skyrmions in MXenes from high-fidelity first-principles calculations (通过高保真第一性原理计算在MXenes中实现单极和双极本征斯格明子)

Arnab Kabiraj & Santanu Mahapatra 

Abstract

Magnetic skyrmions, which are topologically protected tiny spin textures, have emerged as information carriers in energy-efficient logic and memory devices. Skyrmions are commonly realized by inducing large Dzyaloshinskii–Moriya interaction (DMI) in the interface of heavy metal heterolayers. With the advent of two-dimensional magnetism, it is being envisioned to host intrinsic skyrmions in a monolayer, which will be free from any interfacial defect and stacking order. Here using high-fidelity exchange-correlation functional-based first-principles calculations, we investigate such a possibility in methodically designed non-centrosymmetric MXene structures. From a search space of about 3000 materials, our customized high-throughput computational pipeline systematically harnesses out-of-the-plane and in-plane magnetism along with strong DMI to realize typical ‘unipolar’ skyrmions in 78 materials and exotic ‘bipolar’ skyrmions in 13 materials. Micromagnetic and atomistic Monte Carlo simulations further reveal that skyrmions in some of these materials may be stable at room temperature without any external magnetic field. Our study may pave the way for the practical realization of skyrmions-based information technology.

摘要

磁性斯格明子，作为拓扑保护的微小自旋纹理，已成为高能效逻辑和存储设备中的信息载体。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。随着二维磁性的出现，人们设想在单层中实现本征斯格明子，这将摆脱任何界面缺陷和堆叠顺序的限制。在本文中，我们使用基于高保真交换–关联泛函的第一性原理计算，研究了在有条理地设计的非中心对称MXene结构中的实现以上设想的可能性。从大约3000种材料的搜索空间中，我们定制的高通量计算流程系统地利用平面内和平面外磁性以及强DMI来实现78种材料中典型的“单极性”斯格明子和13种材料中奇异的“双极性”斯格明子。微磁和原子级蒙特卡罗模拟进一步揭示了这些材料中的一些斯格明子在没有任何外部磁场的情况下可能在室温下稳定。我们的研究可能为基于斯格明子的信息技术的实际实现铺平道路。