Helimagnons in a chiral ground state of the pyrochlore antiferromagnets

TL;DR

This paper theoretically investigates helimagnon excitations in chiral helical magnetic states of pyrochlore antiferromagnets, revealing anisotropic dispersion relations and mechanisms for relieving magnetic frustration, with results aligning with experimental data.

Contribution

It introduces a theoretical framework for helimagnon excitations in pyrochlore antiferromagnets and connects the effective theory to smectic liquid crystal symmetry.

Findings

Computed low-energy spin-wave spectrum showing characteristic helimagnon dispersion

Demonstrated agreement between dynamics simulations and experimental spectra

Clarified mechanisms for relieving magnetic frustration in these compounds

Abstract

The Goldstone mode in a helical magnetic phase, also known as the helimagnon, is a propagating mode with a highly anisotropic dispersion relation. Here we study theoretically the helimagnon excitations in a complex chiral ground state of pyrochlore antiferromagnets such as spinel CdCr2O4 and itinerant magnet YMn2. We show that the effective theory of the soft modes in the helical state possesses a symmetry similar to that of smectic liquid crystals. We compute the low-energy spin-wave spectrum based on a microscopic spin Hamiltonian and find a dispersion relation characteristic of the helimagnons. By performing dynamics simulations with realistic model parameters, we also obtain an overall agreement between experiment and the numerical spin-wave spectrum. Our work thus also clarifies the mechanisms that relive the magnetic frustration in these compounds.