Heat Capacity of Gadolinium near the Curie Point

Abstract

The dependence of the heat capacity of gadolinium on temperature has been observed close to the ferromagnetic Curie point at about 18\ifmmode^\circ\else\textdegree\fi{}C. An "ac" or temperature-modulation method allowed the use of very small single-crystal samples. The heat-capacity peak for our best sample is rounded in a range of ${\mathrm{\textonehalf{}}}^{\mathrm{\ifmmode^\circ\else\textdegree\fi{}}}$ at the Curie point (${T}_{C}$). Outside this region, good powerlaw fits are obtained for a range of values of the critical exponents $\ensuremath{\alpha}$ (above ${T}_{C}$) and ${\ensuremath{\alpha}}^{\ensuremath{'}}$ (below ${T}_{C}$), the choice of which depends on the choice of ${T}_{C}$. The entire set of data, including those in the rounded region, fits an expression derived from a simple macroscopic model of rounding. The ${T}_{C}$ specified by this fit makes $\ensuremath{\alpha}=\ensuremath{-}0.09+0.05$ and ${\ensuremath{\alpha}}^{\ensuremath{'}}=\ensuremath{-}0.32\ifmmode\pm\else\textpm\fi{}0.05$. Tables of recent theoretical and experimental results are included for comparison. Our results on Curie point and rounding are in disagreement with recent conjectures of Cadieu and Douglass for gadolinium.