Magnetocaloric effect in pyrochlore antiferromagnet Gd2Ti2O7

TL;DR

This study investigates the magnetocaloric effect in Gd2Ti2O7, revealing its potential for efficient low-temperature cooling due to persistent magnetic entropy and gapless local modes, supported by experiments and Monte Carlo simulations.

Contribution

It demonstrates the unique magnetocaloric properties of Gd2Ti2O7, highlighting its potential for magnetic refrigeration and providing a theoretical and experimental analysis of its entropy behavior.

Findings

Significant temperature decrease below the Curie-Weiss constant.

Optimal cooling in the field range 120-60 kOe.

Good agreement between Monte Carlo simulations and experiments.

Abstract

An adiabatic demagnetization process is studied in Gd2Ti2O7, a geometrically frustrated antiferromagnet on a pyrochlore lattice. In contrast to conventional paramagnetic salts, this compound can exhibit a temperature decrease by a factor of ten in the temperature range below the Curie-Weiss constant. The most efficient cooling is observed in the field interval between 120 and 60 kOe corresponding to a crossover between saturated and spin-liquid phases. This phenomenon indicates that a considerable part of the magnetic entropy survives in the strongly correlated state. According to the theoretical model, this entropy is associated with a macroscopic number of local modes remaining gapless till the saturation field. Monte Carlo simulations on a classical spin model demonstrate good agreement with the experiment. The cooling power of the process is experimentally estimated with a view to possible technical applications. The results for Gd2Ti2O7 are compared to those for Gd3Ga5O12, a well-known material for low temperature magnetic refrigeration.