Crystal fields and magnetic structure of the Ising antiferromagnet Er3Ga5 O12

Rare-earth garnets are an exciting playground for studying the exotic magnetic properties of the frustrated hyperkagome lattice. Here we present a comprehensive study of the single ion and collective magnetic properties of the garnet Er3Ga5O12. Using inelastic neutron scattering, we find a crystal-field ground-state doublet for Er3+ with strong Ising anisotropy along local [100] axes. Magnetic susceptibility and heat-capacity measurements provide evidence for long-range magnetic ordering with TN=0.8 K, and no evidence for residual entropy is found when cooling through the ordering transition. Neutron powder diffraction reveals that the ground-state spin configuration corresponds to the six-sublattice, Ising antiferromagnetic state (Γ3) common to many of the rare-earth garnets. However, we also found that μSR appears to be insensitive to the ordering transition in this material, in which a low-temperature relaxation plateau was observed with no evidence of spontaneous muon precession. The combined muon and neutron results may be indicative of a dynamical ground state with a relatively long correlation time. Despite this potential complication, our work indicates that Er3Ga5O12 is an excellent model system for studying the complex metamagnetism expected for a multiaxis antiferromagnet.