Field-induced phase diagram of the XY pyrochlore antiferromagnetEr2Ti2O7

Abstract

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], [110] and [111], the refined field induced magnetic structures are derived from the zero field ψ2 and ψ3 states of the Γ5 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 ψ3 structure at a characteristic field H 001 c = 43 mT. For [110] and [111], the spins are continuously tilted by the field from the ψ2 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 [110], 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. arXiv:1701.07220v2 [cond-mat.str-el]

Frustrated Quantum Rare-Earth Pyrochlores

“…The effect of a magnetic field on Er 2 Ti 2 O 7 has a number of interesting regimes, such as quantum criticality in a [110] field [61], as well as rich physics at low-fields where aspects of the order-by-disorder come into play. This low-field behavior has been explored in detail in recent theoretical [65] and experimental [64,66] studies. Due to the small energy scales, the competition between the order-by-disorder selection and the selection by the applied field occurs at small magnetic fields, of order 0.5 T. This selection is highly direction dependent, with qualitatively different behavior for ψ 2 and ψ 3 ordering.…”

“…More directly, early inelastic neutron scattering experiments [61] observed an approximately linearly dispersing mode near Q ∼ [111], but could not resolve the gap, bounding it to be ∆ 0.1 meV. More recent detailed inelastic neutron scattering studies [47,59,64] focusing on this mode have resolved the gap and found it so be ∆ ∼ 0.04 − 0.05 meV, an order of magnitude smaller than the naïve energy scale (see Fig. 4).…”

Magnetic interactions and spin dynamics in the bond-disordered pyrochlore fluoride NaCaCo2F7

“…This is in contrast to the known pyrochlore system with XY anisotropy, Er 2 Ti 2 O 7 . In this case a feature is seen in the fielddependent magnetization at about 1 T which shows the expected difference in the absolute value for the three main directions of the cubic system [21][22][23]. The absence of such a difference in NaCaCo 2 F 7 might be caused by an accidental "masking" of XY anisotropy.…”

Measurements of the Heat Capacity of Erbium Titanate Er2Ti2O7

“…In addition, in a number of studies, it was found that besides the phase transition of the first order at a temperature of 1.25 K, another increase in the heat capacity is observed at the temperature below 0.3 K in the heat capacity of the Er 2 Ti 2 O 7 compound. ,− This anomaly is related to the presence of the nuclear Schottky contribution to the specific heat of the compound and was considered in subsequent works. − …”