Magnetic order and single-ion anisotropy in Tb$_3$Ga$_5$O$_{12}$

TL;DR

This study reveals the complex low-temperature magnetic structure of terbium gallium garnet (TGG), showing it as a multiaxial antiferromagnet with strong anisotropy and detailed crystal-field effects, combining neutron scattering and magnetic measurements.

Contribution

It provides the first detailed neutron diffraction and crystal-field analysis of TGG's magnetic order and anisotropy at low temperatures, clarifying its magnetic structure and single-ion properties.

Findings

TGG is a multiaxial antiferromagnet with six sublattices.

Strong easy-axis anisotropy is observed in TGG.

Crystal-field parameters are revised based on neutron scattering data.

Abstract

Terbium gallium garnet (TGG), Tb$_3$Ga$_5$O$_{12}$, is well known for its applications in laser optics, but also exhibits complex low-temperature magnetism that is not yet fully understood. Its low-temperature magnetic order is determined by means of time-of-flight neutron powder diffraction. It is found to be a multiaxial antiferromagnet with magnetic Tb$^{3+}$ ions forming six sublattices of magnetic moments aligned parallel and anti-parallel to the $\langle100\rangle$ crystallographic directions of the cubic unit cell. The structure displays strong easy-axis anisotropy with respect to a two-fold axis of symmetry in the local orthorhombic environment of the Tb$^{3+}$ sites. The crystal-field splitting within the single-ion ground-state manifold is investigated by inelastic neutron scattering on powder samples. A strong temperature dependence of the quasidoublet ground-state is observed and revised parameters of the crystal-field Hamiltonian are given. The results of bulk magnetic susceptibility and magnetisation measurements are in good agreement with values based on the crystal-field model down to 20~K, where the onset of magnetic correlations is observed.