Field-Induced Phase Diagram Of The Xy Pyrochlore Antiferromagnet Er2ti2o7

We explore the field-temperature phase diagram of the XY pyrochlore antiferromagnet Er2Ti2O7 by means of magnetization and neutron diffraction experiments. Depending on the field strength and direction relative to the high symmetry cubic directions [001], [1 (1) over bar0], and [111], the refined field-induced magnetic structures are derived from the zero field.2 and.3 states of the Gamma(5) irreducible representation which describes the ground state of XY pyrochlore antiferromagnets. At low field, domain selection effects are systematically at play. In addition, for [001], a phase transition is reported towards a psi(3) structure at a characteristic field H-c(001) = 43 mT. For [1 (1) over bar0] and [111], the spins are continuously tilted by the field from the psi(2) state, and no phase transition is found while domain selection gives rise to sharp anomalies in the field dependence of the Bragg peaks intensity. For [1 (1) over bar0], these results are confirmed by high resolution inelastic neutron scattering experiments, which in addition allow us to determine the field dependence of the spin gap. This study agrees qualitatively with the scenario proposed theoretically by Maryasin et al. [Phys. Rev. B 93, 100406(R) (2016)], yet the strength of the field-induced anisotropies is significantly different from theory.