Magnetic excitations in the topological semimetal $\mathrm{YbMnSb}_2$

TL;DR

This study uses neutron scattering to explore magnetic excitations in YbMnSb$_2$, revealing localized Mn moments, a detailed magnon spectrum, and significant Mn-topological band coupling, advancing understanding of magnetic-topological interactions.

Contribution

It provides the first detailed magnon spectrum and exchange interaction analysis for YbMnSb$_2$, highlighting the strong interlayer exchange and magnetic-topological coupling.

Findings

Magnetic moments are localized on Mn atoms.

Interlayer exchange is significantly larger than in related compounds.

Coupling between Mn moments and topological bands is prominent.

Abstract

We report neutron scattering measurements on YbMnSb$_2$ which shed new light on the nature of the magnetic moments and their interaction with Dirac fermions. Using half-polarized neutron diffraction we measured the field-induced magnetization distribution in the paramagnetic phase and found that the magnetic moments are well localised on the Mn atoms. Using triple-axis neutron scattering we measured the magnon spectrum throughout the Brillouin zone in the antiferromagnetically ordered phase, and we determined the dominant exchange interactions from linear spin-wave theory. The analysis shows that the interlayer exchange is five times larger than in several related compounds containing Bi instead of Sb. We argue that the coupling between the Mn local magnetic moments and the topological band states is more important in YbMnSb$_2$ than in the Bi compounds.