T-S diagram for gadolinium near the Curie temperature

Abstract

The magnetocaloric effect in polycrystalline Gd was measured at temperatures from 190 to 370 K in applied fields from 1 to 7 T. The magnetocaloric temperature changes were combined with existing zero-field specific heat data to construct a T-S diagram for Gd near the Curie point. Experimental values of ΔT were also compared with values calculated from a simple mean field theory, which predicts rather well both the general shape of the magnetocaloric curve and the relative magnitudes of the temperature changes in various measuring fields. The maximum ΔT with applied field was about 14 K at 7 tesla, and maxima in all applied fiels occurred near 292 K. The relatively large magnetocaloric effect in Gd near room temperature is attractive for potential magnetic refrigeration applications, and the experimental T-S diagram may now be used to refine estimates of the performance of Gd as a solid magnetic refrigerant.