Dispersion and lifetimes of magnons in non-collinear magnets from time dependent density functional theory

TL;DR

This paper presents a novel first-principles computational approach using time-dependent density functional theory to analyze magnon dispersion and lifetimes in non-collinear magnets, revealing complex damping behaviors.

Contribution

The authors develop a new computational scheme based on non-collinear KKR Green's functions to study spin dynamics and magnon decay in non-collinear magnetic materials.

Findings

Identified three Goldstone modes with linear dispersion in the long-wavelength limit.

Magnons exhibit significant Landau damping away from the Brillouin zone center.

Magnon attenuation varies with chirality and is influenced by the spin-polarized band structure.

Abstract

We investigate the spin dynamics of the non-collinear kagome triangular anti-ferromagnet Mn$_3$Rh using linear response time-dependent density functional theory. To this end, we present a novel first principles computational scheme for the evaluation of the dynamical susceptibility based on the non-collinear KKR Green's functions method and a symbolic computer algebra.This approach allows us to address the Landau decay of spin waves into non-collinear electron-hole Stoner pairs being inaccessible to adiabatic methods. Our calculations reveal three distinct Goldstone modes dispersing linearly in the long-wavelength regime giving rise to the three magnon branches and we discuss their non-trivial spatial polarizations. The spin-waves turn out to be defined in the whole Brillouin zone but their Landau damping becomes substantial away from the zone's center. Surprisingly, magnons of comparable momenta and energies can feature, depending on their chirality, considerably different attenuation, in some cases of predominantly resonant character. We trace this effect to the interplay between the magnon eigenvectors and the intrinsically spin-polarized altermagnetic band structure and the resulting spectrum of non-collinear Stoner states.