Anisotropic magnons in a layered honeycomb ferromagnet

TL;DR

This study investigates the magnon spectrum in CrSiTe3, revealing anisotropic magnons and minimal magnon gaps, and explores how out-of-plane couplings influence magnetic transition temperatures.

Contribution

It provides detailed neutron scattering evidence for anisotropic magnons and clarifies the role of out-of-plane couplings in CrSiTe3's magnetic properties.

Findings

Magnon gap in CrSiTe3 is very small or absent.

Out-of-plane couplings increase the magnetic transition temperature.

Anisotropic magnons are observed along the out-of-plane direction.

Abstract

Recent experimental and theoretical studies have suggested a possible Dirac magnon gap in the two-dimensional ferromagnetic semiconductor CrSiTe$_3$. Detailed neutron scattering measurements were performed to shed light on the existence of the magnon gap, and suggest that the gap is very small or non-existent, with previous measurements being complicated by experimental factors. During these measurements, it was found that the out-of-plane couplings could explain the usual property of the increase in the magnetic transition temperature when CrSiTe$_3$ is exfoliated to monolayers. Furthermore, the material was shown to have anisotropic magnons along the out-of-plane direction, through the proposed Dirac point. We speculate that this is due to an exchange anisotropy, though Kitaev-like interactions alone cannot explain the spectra.