Dispersionless spin waves in Gadolinium Gallium Garnet

TL;DR

This study uses neutron scattering to explore high-field spin wave behavior in Gadolinium Gallium Garnet, revealing localized excitations and the effects of dipolar interactions on magnetic states.

Contribution

It demonstrates that the high-field spin wave spectrum in Gd3Ga5O12 is well-described by a spin wave theory including dipolar interactions, highlighting localized excitations.

Findings

Almost dispersionless excitations dominate at large momentum transfers.

Localized spin waves are associated with ten-site rings.

High-field spectrum matches spin wave theory predictions.

Abstract

We report the results of neutron scattering on a powder sample of Gd3Ga5O12 at high magnetic fields. We find that in high fields (B>1.8 T) the system is not fully polarized, but has a small canting of the moments induced by the dipolar interaction. We show that the degree of canting is accurately predicted by the standard Hamiltonian which includes the dipolar interaction. The inelastic scattering is dominated at large momentum transfers by a band of almost dispersionless excitations. We show that these correspond to the spin waves localized on ten site rings, expected for a system described by a nearest neighbor interaction, and that the spectrum at high fields B>1.8 T is well-described by a spin wave theory. The phase for fields <1.8 T is characterized by an antiferromagnetic Bragg peak at (210) and an incommensurate peak.