Helimagnon Bands as Universal Spin Excitations of Chiral Magnets

TL;DR

This study reveals that helimagnon bands are a universal feature of chiral magnets like MnSi, demonstrated through comprehensive neutron scattering and a simple three-parameter model that accurately explains the observed magnetic excitations.

Contribution

It introduces a minimal three-parameter model that universally describes helimagnon bands in chiral magnets, validated by extensive experimental data.

Findings

Helimagnon bands are a universal feature of chiral magnets.

A three-parameter model accurately reproduces all observed spectra.

Strongly coupled helimagnon bands are identified as a key characteristic.

Abstract

MnSi is a cubic compound with small magnetic anisotropy, which stabilizes a helimagnetic spin spiral that reduces to a ferromagnetic and antiferromagnetic state in the long- and short-wavelength limit, respectively. We report a comprehensive inelastic neutron scattering study of the collective magnetic excitations in the helimagnetic state of MnSi. In our study we observe a rich variety of seemingly anomalous excitation spectra, as measured in well over twenty different locations in reciprocal space. Using a model based on only three parameters, namely the measured pitch of the helix, the measured ferromagnetic spin wave stiffness and the amplitude of the signal, as the only free variable, we can simultaneously account for \textit{all} of the measured spectra in excellent quantitative agreement with experiment. Our study identifies the formation of intense, strongly coupled bands of helimagnons as a universal characteristic of systems with weak chiral interactions.