Suppression of Pauling's Residual Entropy in Dilute Spin Ice (Dy$_{1-x}$Y$_x$)$_2$Ti$_2$O$_7$

TL;DR

This study investigates how non-magnetic Y dilution affects the low-temperature entropy of Dy$_2$Ti$_2$O$_7$ spin ice, revealing suppression of residual entropy and suggesting a non-degenerate ground state, supported by experiments and Monte Carlo simulations.

Contribution

It provides new insights into the impact of dilution on spin ice entropy, challenging existing theories about residual entropy in dilute systems.

Findings

Ultra-slow thermal equilibration diminishes with dilution

Low-temperature entropy decreases with increasing Y content

Monte Carlo simulations support experimental observations

Abstract

Around 0.5 K, the entropy of the spin-ice Dy$_2$Ti$_2$O$_7$ has a plateau-like feature close to Pauling's residual entropy derived originally for water ice, but an unambiguous quantification towards lower temperature is prevented by ultra-slow thermal equilibration. Based on specific heat data of (Dy$_{1-x}$Y$_x$)$_2$Ti$_2$O$_7$ we analyze the influence of non-magnetic dilution on the low-temperature entropy. With increasing x, the ultra-slow thermal equilibration rapidly vanishes, the low-temperature entropy systematically decreases and its temperature dependence strongly increases. These data suggest that a non-degenerate ground state is realized in (Dy$_{1-x}$Y$_x$)$_2$Ti$_2$O$_7$ for intermediate dilution. This contradicts the expected zero-temperature residual entropy obtained from a generalization of Pauling's theory for dilute spin ice, but is supported by Monte Carlo simulations.