Low Temperature Specific Heat of Dy$_2$Ti$_2$O$_7$ in the Kagome Ice State

TL;DR

This study investigates the low-temperature specific heat of Dy$_2$Ti$_2$O$_7$ in the Kagome ice state, revealing phase transitions, residual entropy, and coexistence of different spin configurations under varying magnetic fields.

Contribution

It provides new experimental data on specific heat at very low temperatures and identifies a previously unreported peak indicating complex spin state coexistence.

Findings

Confirmation of the first-order phase transition line and critical point.

Discovery of a new specific heat peak at 1.25 T below 0.3 K.

Evidence for coexistence of multiple spin states between 1 T and 1.25 T.

Abstract

We report the specific heat of single crystals of the spin ice compound Dy$_2$Ti$_2$O$_7$ at temperatures down to 100 mK in the so-called Kagome ice state. In our previous paper, we showed the anisotropic release of residual entropy in different magnetic field directions and reported new residual entropy associated with spin frustration in the Kagome slab for field in the [111] direction. In this paper, we confirm the first-order phase transition line in the field-temperature phase diagram and the presence of a critical point at (0.98 T, 400 mK), previously reported from the magnetization and specific-heat data. We newly found another peak in the specific heat at 1.25 T below 0.3 K. One possible explanation for the state between 1 T and 1.25 T is the coexistence of states with different spin configurations including the 2-in 2-out one (Kagome ice state), the 1-in 3-out state (ordered state) and paramagnetic one (free-spin state).