Magnetic topological material provides a great platform for discovering new topological states, such as the axion insulators, the Chern insulators, and the 3D quantum anomalous Hall (QAH) insulators. Recently, MnBi2Te4 was discovered to be the first material realization of an intrinsic antiferromagnetic topological insulator (TI) where the QAH effect was observed at a record high temperature in its two-dimensional limit. Since the interplay of the magnetism and band topology determines their topological natures, understanding and manipulating the magnetism inside magnetic TIs will be crucial. In this talk, I will present our discovery of two new magnetic topological materials MnBi4Te7 and MnBi8Te13, with the former being an intrinsic antiferromagnetic TI and the latter being the first intrinsic ferromagnetic axion insulator [1, 2]. I will then show how chemical doping and external pressure can lead to continuous fine control of the magnetism and band topology in MnBi4Te7 [3, 4, 5], revealing the important role that chemical defects play. Our study provides a rare van der Waals material platform with great structural, magnetic, and topological tunability to realize various magnetic topological states and investigate emergent phenomena arising from the interplay of magnetism and band topology.
 C. W. Hu, et.al, Nature Communications, 11, 97 (2020)
 C. W. Hu, et.al, Science Advances, 6, eaba4275 (2020)
 C. W. Hu, et.al, Phys. Rev. B 104, 054422 (2021)
 T. M. Qian, et. al, Nano Lett., 22, 5523 (2022)
 T. M. Qian, et. al, Phys. Rev. B 106, 045121 (2022)