Spin dynamics of the quantum dipolar magnet Yb$_3$Ga$_5$O$_{12}$ in an external field

TL;DR

This study explores the spin dynamics of Yb$_{3}$Ga$_{5}$O$_{12}$, revealing quantum dipolar behavior through combined experimental and theoretical approaches, including neutron scattering and spin-wave calculations.

Contribution

It provides the first comprehensive analysis of Yb$_{3}$Ga$_{5}$O$_{12}$ as a quantum dipolar magnet using multiple experimental techniques and theoretical modeling.

Findings

Elastic neutron response peaks below 500 mK

Flat excitation modes develop in the inelastic spectrum

Spin-wave calculations match excitation spectrum at 2 T

Abstract

We investigate ytterbium gallium garnet Yb$_{3}$Ga$_{5}$O$_{12}$ in the paramagnetic phase above the supposed magnetic transition at $T_{\lambda} \approx 54$ mK. Our study combines susceptibility and specific heat measurements with neutron scattering experiments and theoretical calculations. Below 500 mK, the elastic neutron response is strongly peaked in the momentum space. Along with that the inelastic spectrum develops flat excitation modes. In magnetic field, the lowest energy branch follows a Zeeman shift in accordance with the field-dependent specific heat data. An intermediate state with spin canting away from the field direction is evidenced in small magnetic fields. In the field of 2 T, the total magnetization almost saturates and the measured excitation spectrum is well reproduced by the spin-wave calculations taking into account solely the dipole-dipole interactions. The small positive Curie-Weiss temperature derived from the susceptibility measurements is also accounted for by the dipole spin model. Altogether, our results suggest that Yb$_{3}$Ga$_{5}$O$_{12}$ is a quantum dipolar magnet.