Zero-temperature magnetic phase diagram for the frustrated antiferromagnet gadolinium gallium garnet

Using the recently developed Locally Optimized Simulated Annealing (LOSA) method, we examine numerically the zero-temperature magnetic phase diagram of gadolinium gallium garnet as a function of external field strength and direction. The field is assumed to lie in a plane generated by two principal crystal axes, as this is the case for which most single-crystal experimental data are available. Spin configurations are generated using LOSA for a total of 132 field vectors, and further refined with a hybrid solution exchange method to obtain minimum energy configurations. Our results show a total of five distinct magnetic phases, including a paramagnetic phase at the highest fields, phases with varied field-induced antiferromagnetic ordering at intermediate fields, and a spin-glass phase at low fields. In each of the phases, we calculate simulated neutron scattering profiles and examine the magnetic ordering. We also include an analysis of the appearance of soft magnon modes in the high-field phase. Results are qualitatively consistent with existing experimental data and allow predictions to be made for further experimental tests.