Thermodynamic properties of quadrupolar states in the frustrated pyrochlore magnet Tb2Ti2O7

Abstract

The low-temperature thermodynamic properties of the frustrated pyrochlore Tb2+xTi2-xO7+y have been studied using the single crystal of x = 0.005 sitting in a long range ordered phase in the x-T phase diagram. We observed that the specific heat exhibits a minimum around 2 K and slightly increases on cooling, similar to a Schottky-like anomaly for canonical spin ices. A clear specific-heat peak observed at Tc = 0.53 K is ascribable to the phase transition to a quadrupolar state, which contributes to a relatively large change in entropy, S ≃ 2.7 J K-1mol-1. However, it is still smaller than R ln 2 for the ground state doublet of the Tb ions. The entropy release persists to higher temperatures, suggesting strong fluctuations associated with spin ice correlations above Tc. We discuss the field dependence of the entropy change for H ∥ [111] and H ∥ [001].