Multiple field-induced phase transitions in the geometrically frustrated dipolar magnet: Gd2Ti2O7

Field-driven phase transitions generally arise from competition between Zeeman energy and exchange or crystal-field anisotropy. Here we present the phase diagram of a frustrated pyrochlore magnet Gd2Ti2O7, where crystal-field splitting is small compared to the dipolar energy. We find good agreement between zero-temperature critical fields and those obtained from a mean-field model. Here, dipolar interactions couple real space and spin space, so the transitions in Gd2Ti2O7 arise from field-induced ``cooperative anisotropy,{''} reflecting the broken spatial symmetries of the pyrochlore lattice.