The dependence of the heat capacity of gadolinium on temperature has been observed close to the ferromagnetic Curie point at about 18°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 ${\mathrm{½}}^{\mathrm{°}}$ at the Curie point ($T_C$). Outside this region, good powerlaw fits are obtained for a range of values of the critical exponents $\alpha$ (above $T_C$) and ${\alpha }^{\prime }$ (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 $\alpha =-0.09+0.05\mathrm{}$ and ${\alpha }^{\prime }=-0.32\mathrm{}\pm 0.05$. 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.

• Received 10 November 1969

DOI:https://doi.org/10.1103/PhysRevB.1.4368