Competing magnetic interactions in the antiferromagnetic topological insulator MnBi${}_2$Te${}_4$

Abstract

The antiferromagnetic (AF) compound MnBi${}_2$Te${}_4$ is suggested to be the first realization of an antiferromagnetic (AF) topological insulator. Here we report on inelastic neutron scattering studies of the magnetic interactions in MnBi${}_2$Te${}_4$ that possess ferromagnetic (FM) triangular layers with AF interlayer coupling. The spin waves display a large spin gap and pairwise exchange interactions within the triangular layer are frustrated due to large next-nearest neighbor AF exchange. The degree of frustration suggests proximity to a variety of magnetic phases, potentially including skyrmion phases, that could be accessed in chemically tuned compounds or upon the application of symmetry-breaking fields.

5 pages, 4 figures