Magnon spectrum of the Weyl semimetal half-Heusler compound GdPtBi

TL;DR

This study maps the magnon spectrum of GdPtBi, revealing sharp spin-wave modes and elucidating magnetic interactions, advancing understanding of its antiferromagnetic order and topological properties.

Contribution

The paper provides the first detailed magnon spectrum of GdPtBi and identifies the dominant magnetic interactions using inelastic neutron scattering and spin-wave theory.

Findings

Magnon spectrum shows two sharp dispersive modes.

GdPtBi is dominated by second-neighbor interactions.

The magnon gap is approximately 0.15 meV.

Abstract

The compound GdPtBi is known as a material where the non-trivial topology of electronic bands interplays with an antiferromagnetic order, which leads to the emergence of many interesting magnetotransport phenomena. Although the magnetic structure of the compound has previously been reliably determined, the magnetic interactions responsible for this type of order remained controversial. In the present study, we employed time-of-flight inelastic neutron scattering to map out the low-temperature spectrum of spin excitations in single-crystalline GdPtBi. The observed spectra reveal two spectrally sharp dispersive spin-wave modes, which reflects the multi-domain state of the $\mathbf{k} = (\frac{1}{2}\frac{1}{2}\frac{1}{2})$ face-centred cubic antiferromagnet in the absence of a symmetry-breaking magnetic field. The magnon dispersion reaches an energy of $\sim 1.1$~meV and features a gap of $\sim 0.15$~meV. Using linear spin-wave theory, we determined the main magnetic microscopic parameters of the compound that provide good agreement between the simulated spectra and the experimental data. We show that GdPtBi is well within the ($\frac{1}{2}\frac{1}{2}\frac{1}{2}$) phase and is dominated by second-neighbor interactions, thus featuring low frustration.