Abstract: Magnetic topological insulators (MTIs) have received considerable attention owing to the demonstration of various quantum phenomena, such as the quantum anomalous Hall effect and topological magnetoelectric effect. The intrinsic superlatticelike layered MTIs MnBi2Te4/(Bi2Te3)n have been extensively investigated mainly through transport measurements; however, a direct investigation of their superlattice-sensitive magnetic behaviors is relatively rare. In this paper, we report a microscopic real space investigation of the magnetic phase behaviors in MnBi4Te7 using cryogenic magnetic force microscopy. The intrinsic robust A type antiferromagnetic (AFM), surface spin-flip (SSF) + AFM, ferromagnetic (FM) + SSF + AFM, and forced FM phases are sequentially visualized via the increased external magnetic field, consistent with the magnetic behavior in the M-H curve. The temperature-dependent magnetic phase evolution behaviors are further investigated to obtain a complete H-T phase diagram of MnBi4Te7. Tentative local phase manipulation via the stray field of the magnetic tip is demonstrated by transforming the AFM into the FM phase in the surface layers of MnBi4Te7. Our study provides key real-space ingredients for understanding the complicated magnetic, electronic, and topological properties of such intrinsic MTIs and suggests new directions for manipulating spin textures and locally controlling their exotic properties.
Two-dimensional (2D) magnetic materials with magnetic anisotropy can form magnetic order at finitetemperature and monolayer limit. Their macroscopic magnetism is closely related to the number of layers andstacking forms, and their magnetic exchange coupling can be regulated by a variety of external fields. Thesenovel properties endow 2D magnetic materials with rich physical connotation and potential application value,thus having attracted extensive attention. In this paper, the recent advances in the experiments and theoreticalcalculations of 2D magnets are reviewed. Firstly, the common magnetic exchange mechanisms in several 2Dmagnetic materials are introduced. Then, the geometric and electronic structures of some 2D magnets and theirmagnetic coupling mechanisms are introduced in detail according to their components. Furthermore, we discusshow to regulate the electronic structure and magnetism of 2D magnets by external (field modulation andinterfacial effect) and internal (stacking and defect) methods. Then we discuss the potential applications ofthese materials in spintronics devices and magnetic storage. Finally, the encountered difficulties and challengesof 2D magnetic materials and the possible research directions in the future are summarized and prospected. DOI: 10.7498/aps.71.20220301
Kui Huang (黄逵), Zhenxian Li (李政贤), Deping Guo (郭的坪), Haifeng Yang (杨海峰), Yiwei Li (李一苇), Aiji Liang (梁爱基), Fan Wu (吴凡), Lixuan Xu (徐丽璇), Lexian Yang (杨乐仙), Wei Ji (季威), Yanfeng Guo (郭艳峰), Yulin Chen (陈宇林)* and Zhongkai Liu (柳仲楷)*
Abstract
As a van der Waals ferromagnet with high Curie temperature, Fe5–xGeTe2 has attracted tremendous interests recently. Here, using high-resolution angle-resolved photoemission spectroscopy (ARPES), we systematically investigated the electronic structure of Fe5–xGeTe2 crystals and its temperature evolution. Our ARPES measurement reveals two types of band structures from two different terminations with slight kz evolution. Interestingly, across the ferromagnetic transition, we observed the merging of two split bands above the Curie temperature, suggesting the band splitting due to the exchange interaction within the itinerant Stoner model. Our results provide important insights into the electronic and magnetic properties of Fe5–xGeTe2 and the understanding of magnetism in a two-dimensional ferromagnetic system.
Two-dimensional magnetic semiconductors provide a platform for studying physical phenomena at atomically thin limit, and promise magneto-optoelectronic devices application. Here, we report light helicity detectors based on graphene-CrI3-graphene vdW heterostructures. We investigate the circularly polarized light excited current and reflective magnetic circular dichroism (RMCD) under various magnetic fields in both monolayer and multilayer CrI3 devices. The devices exhibit clear helicity-selective photoresponse behavior determined by the magnetic state of CrI3. We also find abnormal negative photocurrents at higher bias in both monolayer and multilayer CrI3. A possible explanation is proposed for this phenomenon. Our work reveals the interplay between magnetic and optoelectronic properties in CrI3 and paves the way to developing spin-optoelectronic devices.
