Heat capacity of EuO near the Curie temperature

Abstract

Precision measurements of the heat capacity $C_p$ of the Heisenberg ferromagnet EuO near the Curie temperature $T_c\approx 69.3$ K are reported. The data are for $64\le T\le 73$ K. When they are analyzed in terms of pure-power-law singularities over the range $0.003\le \mathrm{}\left|t\right|\mathrm{}\equiv |1-\frac{T}{T_c}|\le 0.07$, they permit equal exponents $\alpha$ and ${\alpha }^{\prime }$ above and below the transition, and a continuous specific heat at $T_c$. They yield $\alpha ={\alpha }^{\prime }=-0.044\mathrm{}\pm 0.01$ and an amplitude ratio $\frac{A}{A^{\prime }}=1.22\mathrm{}\pm 0.06$ when $C_p$ is assumed to be continuous. Although these results are consistent with scaling predictions, they disagree with estimates based on renormalization-group calculations for isotropic ferromagnets with dipolar interactions. When, in addition to the leading power-law term, singular correction terms are also included in the analysis and $C_p$ is assumed to be continous at $T_c$, one finds $\alpha ={\alpha }^{\prime }=-0.10\mathrm{}\pm 0.05$, $\frac{A}{A^{\prime }}=1.50\mathrm{}\pm 0.2$, and a correction exponent $x=0.56\mathrm{}\pm 0.2$. These latter results are consistent with all theoretical predictions.