Spin dynamics in the antiferromagnetic topological insulator MnBi₄Te₇

MnBi_2+2nTe_4+3n are promising topological insulators (TI) where the natural intergrowth of magnetic layers and TI layers provides a unique platform for studying the interplay between magnetism and topological electronic states. Here we present results from our inelastic neutron scattering study on single crystals MnBi₄Te₇. The spin waves at base temperature can be described by a Heisenberg model with intra-layer interactions and the single-ion anisotropy. Through comparison to the spin waves in MnBi₂Te₄, we discuss the changes in the intra- and inter-layer magnetic interactions and the single-ion anisotropy across the Mn-Bi-Te series. At higher temperatures, MnBi₄Te₇ shows quasielastic scattering at magnetic peak positions below and above Neel temperature T_N, which indicates the existence of two-dimensional magnetic correlations. We extract the correlation lengths and the damping parameters at various temperatures and discuss the influence on magnetism due to the reduced dimensions.