Magnetocaloric effect in pyrochlore antiferromagnet Gd₂Ti₂O₇

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 10 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 until 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.