海归学者发起的公益学术平台
分享信息，整合资源
交流学术，偶尔风月
以面内磁化为特征的二维XY铁磁体已经取得了一定的研究进展。然而，根据 Mermin-Wagner 定理, 由于增强的热涨落, 长程磁有序很难在二维XY铁磁体中存在，这也在一定程度上限制了其在自旋电子学中的应用。因此，实现二维XY铁磁体的易磁化轴从面内向面外转变，对基础研究和实际应用都具有重要意义。在诸多调控手段中，通过纯电学的方式实现该目标是最理想的。虽然外加电场可以操纵二维XY铁磁体的易磁化轴，但是这种调控是易失的，将不可避免地引起能耗问题，这对XY铁磁体在低功耗器件中的应用带来了巨大的挑战。
Fig. 1 Schematic representation of transition between 2D XY and Heisenberg models.
来自山东大学晶体材料国家重点实验室的赵显教授、李妍璐教授和济南大学自旋电子学研究所的李胜世科研团队设计了基于XY铁磁单层VBi
2
Te
4
和铁电单层In
2
Se
3
的多铁范德华异质结。在该异质结中，铁电层极化方向的翻转可以诱导铁磁层的易磁轴由面内转换为面外，使二维XY铁磁体转变为海森堡铁磁体，同时还实现了长程磁有序的关与开。根据蒙特卡洛模拟，具有面外磁各向异性的单层VBi
2
Te
4
的居里温度可达76K。此外，基于二阶微扰理论定性地解释了多铁范德华异质结中与铁电极化有关的磁各向异性。
Fig. 2 Geometric structures of free-standing monolayers and
heterostructures.
值得注意的是，随着磁各向异性改变，单层VBi
2
Te
4
还实现了从半导体到半金属态的转变。这使得In
2
Se
3
的铁电极化态和VBi
2
Te
4
的磁各向异性都可以通过VBi
2
Te
4
的导电状态来进行表征。鉴于此，作者从多铁范德华异质结出发，设计了一种非易失的高密度数据存储器件。此外，研究发现，双轴应变能够有效地调控多铁范德华异质结中单层VBi
2
Te
4
的半金属性质和磁晶各向异性能。该研究为磁各向异性和半金属性的非易失性电调控提供了一个良好的平台，推动了多铁范德华异质结在先进自旋电子器件中的实际应用。
Fig. 6 Strain-induced change in MAE.
该文近期发表于
npj Computational Materials
9
：223
(2023)
，
英文标题与摘要如下，点击左下角“
阅读原文
”可以自由获取论文PDF。
Exploitable magnetic anisotropy and half-metallicity controls in multiferroic van der Waals heterostructure
Yaping Wang, Xinguang Xu，Weixiao Ji，Shengshi Li，Yanlu Li & Xian Zhao
Two-dimensional (2D) XY ferromagnets have drawn pronounced interest in recent years, but the characteristic of easy-plane magnetization restricts their application in spintronics to some extent. Here, we propose a general strategy for constructing multiferroic van der Waals heterostructures, aiming to achieve electrical control over the magnetic anisotropy in 2D XY ferromagnets. The validity of this strategy is verified by the heterostructure composed of ferromagnetic VBi2Te4 and ferroelectric In2Se3 monolayers. By manipulating the polarized states of In2Se3, the VBi2Te4 can be reversibly transformed between 2D XY and Heisenberg ferromagnets, characterized by the switching of easy magnetization axis between in-plane and out-of-plane directions. More interestingly, accompanied by the changes in magnetic anisotropy, the VBi2Te4 also demonstrates a phase transition from a semiconductor to a half-metal state, which can be ascribed to the band alignment and interfacial charge transfer. The switchable magnetic and electronic properties enable the heterostructure to be utilized in nonvolatile memory and logic devices. Additionally, the half-metallicity and magnetocrystalline anisotropy energy of the heterostructure can be effectively tuned by biaxial strain. These findings not only pave the way for electrically nonvolatile control of 2D XY ferromagnet, but also facilitate the development of interfacial magnetoelectric physics and applications.
