Specific heat and resistivity of gadolinium near the Curie point in external magnetic fields

Abstract

A modification of the ac calorimetric technique has been used to test the proportionality of the specific heat and temperature derivative of the basal-plane resistivity of gadolinium through the Curie point. Because of a large temperature-dependent background to the resistivity derivative, a direct comparison of the critical contributions to the two quantities was impossible. It was found, however, that the background was insensitive to applied magnetic fields so that a direct comparison of the deviation of the specific heat at a finite field from its zero-field value with the similar deviation of the resistivity derivative demonstrated the proportionality of the two quantities. In applied fields below 585 Oe, a "kink point" was observed in the specific heat below $T_C$ which moved to lower temperatures with increasing fields. Such an effect has been predicted to occur at fields and temperatures for which the internal magnetic field vanishes. The specific heat in several fields above 585 Oe was compared with the predictions of scaling laws and with the linear approximation to the parametric equation of state. Reasonable agreement between the data and the specific-heat scaling function predicted by the linear model could only be obtained by using an unrealistic value of the critical exponent describing the zero-field specific heat.