斯格明子是拓?fù)浔Ｗo(hù)的非共線磁性模式，自旋排列成漩渦狀，表現(xiàn)為納米級(jí)準(zhǔn)粒子，可以通過(guò)自旋極化電流和磁場(chǎng)進(jìn)行操縱。具有穩(wěn)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(chǔ)和處理設(shè)備。例如，邏輯1和0可以由斯格明子的存在和缺失來(lái)表示。

Fig. 1 Anatomy of the MXenes.

斯格明子通常通過(guò)在重金屬異質(zhì)層界面誘導(dǎo)大的Dzyaloshinskii-Moriya相互作用（DMI）來(lái)實(shí)現(xiàn)。實(shí)驗(yàn)表明，一些鐵磁/重金屬異質(zhì)結(jié)構(gòu)，如Fe/Ir (111)、 Ir/Fe/Co/Pt、Pt/Co/MgO等，可以產(chǎn)生較大的DMI。這是因?yàn)椋砻娴姆囱輰?duì)稱性喪失以及由重金屬和Rashba效應(yīng)導(dǎo)致的強(qiáng)自旋–軌道耦合，從而引出較大的DMI。

理論也預(yù)測(cè)在Co表面沉積的二維材料如石墨烯和hBN會(huì)產(chǎn)生斯格明子態(tài)。然而，這些異質(zhì)結(jié)的界面缺陷以及層間堆疊順序?qū)?/span>DMI的提升不利。因此，設(shè)計(jì)具有反演不對(duì)稱性的單層材料，以創(chuàng)造有利于穩(wěn)定斯格明子的條件，是非常有價(jià)值的。

來(lái)自印度科學(xué)院班加羅爾電子系統(tǒng)工程系的Santanu Mahapatra教授團(tuán)隊(duì)，結(jié)合基于高保真交換–關(guān)聯(lián)泛函的第一性原理計(jì)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(kāi)發(fā)了一個(gè)全自動(dòng)的高通量計(jì)算工作流，嚴(yán)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(wěn)定斯格明子的材料。

此外，作者還發(fā)現(xiàn)了一些材料能夠在室溫下無(wú)需任何外部磁場(chǎng)即可形成垂直于平面的斯格明子，這對(duì)于設(shè)計(jì)與當(dāng)前技術(shù)兼容的基于斯格明子的設(shè)備很有價(jià)值。作者的工作可以加速并有助于斯格明子基自旋電子學(xué)的工程化。該文近期發(fā)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(guò)高保真第一性原理計(jì)算在MXenes中實(shí)現(xiàn)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?fù)浔Ｗo(hù)的微小自旋紋理，已成為高能效邏輯和存儲(chǔ)設(shè)備中的信息載體。斯格明子通常通過(guò)在重金屬異質(zhì)層界面誘導(dǎo)大的Dzyaloshinskii-Moriya相互作用（DMI）來(lái)實(shí)現(xiàn)。隨著二維磁性的出現(xiàn)，人們?cè)O(shè)想在單層中實(shí)現(xiàn)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(guān)聯(lián)泛函的第一性原理計(jì)算，研究了在有條理地設(shè)計(jì)的非中心對(duì)稱MXene結(jié)構(gòu)中的實(shí)現(xiàn)以上設(shè)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(jì)算流程系統(tǒng)地利用平面內(nèi)和平面外磁性以及強(qiáng)DMI來(lái)實(shí)現(xiàn)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(jí)蒙特卡羅模擬進(jìn)一步揭示了這些材料中的一些斯格明子在沒(méi)有任何外部磁場(chǎng)的情況下可能在室溫下穩(wěn)定。我們的研究可能為基于斯格明子的信息技術(shù)的實(shí)際實(shí)現(xiàn)鋪平道路。