Determination of the Entropy via Measurement of the Magnetization: Application to the Spin ice Dy2Ti2O7

TL;DR

This paper introduces a magnetization-based method using Maxwell's relations to accurately determine residual entropy in spin ice Dy2Ti2O7, providing insights into magnetic monopoles and phase crossover phenomena.

Contribution

It presents a novel, calorimetry-independent approach to measure residual entropy in spin ice using magnetization data, validated on Dy2Ti2O7.

Findings

Method confirms residual entropy measurement aligns with calorimetric results

Identifies a field-induced crossover from spin ice to paramagnetic behavior

Provides insight into entropy dependence on magnetic moments in spin ice

Abstract

The residual entropy of spin ice and other frustrated magnets is a property of considerable interest, yet the usual way of determining it, by integrating the heat capacity, is generally ambiguous. Here we note that a straightforward alternative method based on Maxwell's thermodynamic relations can yield the residual entropy on an absolute scale. The method utilises magnetization measurements only and hence is a useful alternative to calorimetry. We confirm that it works for spin ice, Dy2Ti2O7, which recommends its application to other systems. The analysis described here also gives an insight into the dependence of entropy on magnetic moment, which plays an important role in the theory of magnetic monopoles in spin ice. Finally, we present evidence of a field-induced crossover from correlated spin ice behaviour to ordinary paramagnetic behaviour with increasing applied field, as signalled by a change in the effective Curie constant.