High-Resolution Specific Heat of CoCl2· 6H2O

Abstract

The specific heat of a single crystal of Co${\mathrm{Cl}}_{2}$ \ifmmode\cdot\else\textperiodcentered\fi{} 6${\mathrm{H}}_{2}$O has been measured with high resolution near ${T}_{N}=2.29$ K. The data were fitted to the usual asymptotic form $C=A{\ensuremath{\epsilon}}^{\ensuremath{-}\ensuremath{\alpha}}+B$, where $\ensuremath{\epsilon}=|1\ensuremath{-}\frac{T}{{T}_{N}}|$, using several different techniques. An examination of the gradient $\frac{\ensuremath{\partial}C}{\ensuremath{\partial}T}$ showed that the critical region was limited to $\ensuremath{\epsilon}\ensuremath{\lesssim}7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ and that for $\ensuremath{\epsilon}\ensuremath{\lesssim}4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ the specific heat was rounded. The data were found to fit the asymptotic form for $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\ensuremath{\lesssim}\ensuremath{\epsilon}\ensuremath{\lesssim}7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ with ${\ensuremath{\alpha}}^{\ensuremath{'}}=\ensuremath{-}0.19\ifmmode\pm\else\textpm\fi{}0.04$ for $T<{T}_{N}$ and $\ensuremath{\alpha}=0.34\ifmmode\pm\else\textpm\fi{}0.05$ for $T>{T}_{N}$. It was also found that the observed rounding could be predicted by treating the sample as a system of microcrystals having a finite distribution of ordering temperatures. It was thus possible to produce a reasonable fit to all the data for $\ensuremath{\epsilon}<7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ using the above values of ${\ensuremath{\alpha}}^{\ensuremath{'}}$ and $\ensuremath{\alpha}$ which were determined from the data in the "unrounded critical region." It was further found that the results of a previous experiment in another laboratory could also be fitted over the entire critical region using the above values of ${\ensuremath{\alpha}}^{\ensuremath{'}}$ and $\ensuremath{\alpha}$ with a somewhat broader distribution of ordering temperatures.