Adiabatic demagnetization of a pyrochlore antiferromagnet Gd2Ti2O7

An adiabatic demagnetization process is studied in the pyrochlore antiferromagnet Gd2Ti2O7. A strong cooling of the sample is observed by decreasing magnetic field in the range 120-60 kOe corresponding to a crossover between saturated and spin-liquid phases. This phenomenon indicates that a considerable part of the magnetic entropy associated with a macroscopic number of local soft modes survives in the strongly correlated paramagnetic state. Monte Carlo simulations demonstrate good agreement with the experiment. The cooling power of the process is experimentally estimated with a view to possible technical applications. The results on Gd2Ti2O7 are compared to those for Gd3Ga5O12, a related material for low-temperature magnetic cooling. (c) 2004 Elsevier B.V. All rights reserved.