Abstract: Magnetic topological insulators (TI) are of interest for potential applications in dissipationless quantum transport, optical, and magnetoelectric responses. These materials couple topological electronic states with magnetism so that the symmetry of the magnetic states determines the topological electronic states, offering an opportunity for manipulation of the topological states through magnetism.

In this talk, I will briefly review the magnetic TIs, particularly the intrinsically magnetic TIs in the Mn-Bi-Te family, including MnBi2Te4 and MnSb2Te4. The focus of the talk will be on the understanding of magnetism in these TIs. I will present the inelastic neutron scattering results of the spin dynamics in MnBi2Te4, MnBi4Te7, and MnSb2Te4. I will demonstrate how magnetic interactions and anisotropies were determined in these materials and discuss their implications. In MnSb2Te4, I will identify the experimental signature of strong antiferromagnetic coupling due to the presence of Mn-Sb anti-site mixing and propose a defect-driven scheme with competing interlayer interactions which can explain the observed defect-dependent magnetic ground states in MnSb2Te4.