Role of non-magnetic spacers in the magnetic interactions of antiferromagnetic topological insulators MnBi$_{4}$Te$_{7}$ and MnBi$_{2}$Te$_{4}$

TL;DR

This study investigates how non-magnetic spacers affect magnetic interactions in antiferromagnetic topological insulators MnBi$_{4}$Te$_{7}$ and MnBi$_{2}$Te$_{4}$, revealing weaker interlayer coupling in MnBi$_{4}$Te$_{7}$ due to inserted layers.

Contribution

It provides new insights into magnetic interactions in MnBi$_{4}$Te$_{7}$, highlighting the role of non-magnetic layers and establishing transferable magnetic energy scales for related materials.

Findings

Interlayer magnetic coupling is weaker in MnBi$_{4}$Te$_{7}$ compared to MnBi$_{2}$Te$_{4}$.

Single-ion anisotropy and intralayer exchanges are similar in both compounds.

Non-magnetic layers modulate interlayer magnetic interactions without affecting intra-layer properties.

Abstract

MnBi$_{4}$Te$_{7}$ belongs to a family of antiferromagnetic topological insulators. It forms a natural heterostructure of magnetic (septuple) and non-magnetic (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 MnBi$_{4}$Te$_{7}$ as compared to MnBi$_{2}$Te$_{4}$ due to the insertion of non-magnetic 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 MnBi$_2$Te$_4$-Bi$_2$Te$_3$ heterostructures.