Motivated by predictions of a spin-ice state on the Ising garnet lattice, we have completed neutron-scattering experiments on single crystals of ${\text{Ho}}_3{\text{Ga}}_5{\text{O}}_{12}$. Our results show that although the ${\text{Ho}}^{3+}$ spins have Ising-type character with an easy-axis anisotropy, the low-temperature ground state has coexisting long-range- and short-range-ordered spins and is therefore not an ice state. Inelastic neutron-scattering measurements reveal the presence of low-lying crystal-field states that develop a softening at the onset of short-range magnetic ordering. We suggest that the specific tuning of the exchange and dipolar interactions, along with the accessibility of these low-lying excitations, conspire to drive the system to a disordered state.

• Received 11 August 2008

DOI:https://doi.org/10.1103/PhysRevB.78.140406