Momentum-dependent magnon lifetime in the metallic non-collinear triangular antiferromagnet CrB2

TL;DR

This study investigates magnon decay in the metallic non-collinear antiferromagnet CrB2 using inelastic neutron scattering, revealing unusual momentum-dependent damping and higher-order decay processes not explained by linear theory.

Contribution

It provides the first comprehensive experimental analysis of spin dynamics and magnon decay mechanisms in metallic non-collinear antiferromagnets, highlighting higher-order effects.

Findings

Magnon linewidth shows unusual momentum dependence.

Intrinsic damping arises from two-magnon decay and Stoner continuum.

Experimental evidence of higher-order decay effects in metallic antiferromagnets.

Abstract

Non-collinear magnetic order arises for various reasons in several magnetic systems and exhibits interesting spin dynamics. Despite its ubiquitous presence, little is known of how magnons, otherwise stable quasiparticles, decay in these systems, particularly in metallic magnets. Using inelastic neutron scattering, we examine the magnetic excitation spectra in a metallic non-collinear antiferromagnet CrB$_{2}$, in which Cr atoms form a triangular lattice and display incommensurate magnetic order. Our data show intrinsic magnon damping and continuum-like excitations that cannot be explained by linear spin wave theory. The intrinsic magnon linewidth $\Gamma(q,E_{q})$ shows very unusual momentum dependence, which our analysis shows to originate from the combination of two-magnon decay and the Stoner continuum. By comparing the theoretical predictions with the experiments, we identify where in the momentum and energy space one of the two factors becomes more dominant. Our work constitutes a rare comprehensive study of the spin dynamics in metallic non-collinear antiferromagnets. It reveals, for the first time, definite experimental evidence of the higher-order effects in metallic antiferromagnets.