Role of nonmagnetic spacers in the magnetic interactions of antiferromagnetic topological insulators MnBi4⁢Te7 and MnBi2⁢Te4

Abstract

MnBi4⁢Te7 belongs to a family of antiferromagnetic topological insulators. It forms a natural heterostructure of magnetic (septuple) and nonmagnetic (quintuple) topological blocks. Here, we explore the magnetism and magnetic interactions in this compound using inelastic neutron scattering. We find that the interlayer magnetic coupling is much weaker in MnBi4⁢Te7 as compared to MnBi2⁢Te4 due to the insertion of nonmagnetic quintuple layers in the former. However, other key magnetic energy scales residing within a single septuple block, the single-ion anisotropy and long-range intralayer exchanges, are essentially the same. This identifies a transferable set of magnetic interactions applicable to the extended family of magnetic topological insulators based on MnBi2⁢Te4−Bi2⁢Te3 heterostructures.