Coexisting Ferromagnetic–Antiferromagnetic Phases and Manipulation in a Magnetic Topological Insulator MnBi4Te7

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 superlattice-like 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.