斯格明子是拓撲保護的非共線磁性模式，自旋排列成漩渦狀，表現為納米級準粒子，可以通過自旋極化電流和磁場進行操縱。具有穩定斯格明子的材料可用于制造超低功耗的微觀尺度信息存儲和處理設備。例如，邏輯1和0可以由斯格明子的存在和缺失來表示。

Fig. 1 Anatomy of the MXenes.

斯格明子通常通過在重金屬異質層界面誘導大的Dzyaloshinskii-Moriya相互作用（DMI）來實現。實驗表明，一些鐵磁/重金屬異質結構，如Fe/Ir (111)、 Ir/Fe/Co/Pt、Pt/Co/MgO等，可以產生較大的DMI。這是因為，表面的反演對稱性喪失以及由重金屬和Rashba效應導致的強自旋–軌道耦合，從而引出較大的DMI。

理論也預測在Co表面沉積的二維材料如石墨烯和hBN會產生斯格明子態。然而，這些異質結的界面缺陷以及層間堆疊順序對DMI的提升不利。因此，設計具有反演不對稱性的單層材料，以創造有利于穩定斯格明子的條件，是非常有價值的。

來自印度科學院班加羅爾電子系統工程系的Santanu Mahapatra教授團隊，結合基于高保真交換–關聯泛函的第一性原理計算以及微磁和蒙特卡羅模擬，探索了含有單層磁性金屬的MXene特定子類中斯格明子的存在。作者開發了一個全自動的高通量計算工作流，嚴格掃描了大約3000種材料的大空間，最終得到了91種有望形成穩定斯格明子的材料。

此外，作者還發現了一些材料能夠在室溫下無需任何外部磁場即可形成垂直于平面的斯格明子，這對于設計與當前技術兼容的基于斯格明子的設備很有價值。作者的工作可以加速并有助于斯格明子基自旋電子學的工程化。該文近期發布于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 ?elds. 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-?delity exchange-correlation functional-based ?rst-principles calculations with micromagnetic and Monte Carlo (MC) simulations, to explore a speci?c subclass of MXenes containing a single magnetic metal layer for the presence of skyrmions. A fully automated high-throughput computational work?ow 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 ?eld, 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及其翻譯

Realizing unipolar and bipolar intrinsic skyrmions in MXenes from high-fidelity first-principles calculations (通過高保真第一性原理計算在MXenes中實現單極和雙極本征斯格明子)

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，作為拓撲保護的微小自旋紋理，已成為高能效邏輯和存儲設備中的信息載體。斯格明子通常通過在重金屬異質層界面誘導大的Dzyaloshinskii-Moriya相互作用（DMI）來實現。隨著二維磁性的出現，人們設想在單層中實現本征斯格明子，這將擺脫任何界面缺陷和堆疊順序的限制。在本文中，我們使用基于高保真交換–關聯泛函的第一性原理計算，研究了在有條理地設計的非中心對稱MXene結構中的實現以上設想的可能性。從大約3000種材料的搜索空間中，我們定制的高通量計算流程系統地利用平面內和平面外磁性以及強DMI來實現78種材料中典型的“單極性”斯格明子和13種材料中奇異的“雙極性”斯格明子。微磁和原子級蒙特卡羅模擬進一步揭示了這些材料中的一些斯格明子在沒有任何外部磁場的情況下可能在室溫下穩定。我們的研究可能為基于斯格明子的信息技術的實際實現鋪平道路。