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

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)_nhave 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 MnBi₄Te₇using 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.