Resistivity and specific heat measurements near phase transitions in metals
The ac calorimetry technique for measuring the specific heat has been modified to include a simultaneous measurement of the temperature derivative of the electrical resistivity on the same sample. Measurements are reported on f3-brass and gadolinium. The resistivity derivative of f3~brass is found to be proportional to the specific heat through its order-disorder transition temperature of 466°C. This is in agreement with an extension of the theoretical prediction that the quantities should be proportional in a magnetic system. Measurements of the specific heat and resistivity derivative on the rare earth ferromagnet gadolinium have revealed a previously undetected anomaly in the specific heat along with a peak in the a-axis resistivity derivative at 226°K, where the magnetization vector tilts from the c-axis. The anomalies are suppressed in applied magnetic fields. A model for the temperature dependence of the anisotropy energy is used to describe this tilting transition. Near the Curie temperature of 29l °K, measurements of the specific heat and a-axis resistivity derivative of gadolinium are made in several applied magnetic fields in order to cancel background effects and establish the predicted proportionality. Kinks in the specific heat in small applied fields are explained by demagnetizing effects. At higher fields, the specific heat is compared with the prediction of the linearized parametric equation of state, with inconclusive results.
resistivity, specific heat measurements, phase transition
University of Illinois - Urbana-Champaign
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