Magnetic and Thermal Properties of MnCl2at Liquid Helium Temperatures. II. Specific Heat

The specific heat of anhydrous Mn${\mathrm{Cl}}_2$ has been measured from 1.25° to 4.2°K in a search for the anomaly associated with the magnetic transition observed near 2°K. The measuring techniques are discussed briefly. The results of a series of experiments show two $\lambda$-type anomalies, each of magnitude 12 joules/mole-degree, located at 1.81° and 1.96°K. These two maxima are interpreted as arising from a multiple transition from the paramagnetic to an antiferromagnetic state. A plot of magnetic entropy vs temperature, obtained by integration of the specific heat data, shows that approximately $\frac{2}{3}$ of the available spin entropy has been achieved at the upper transition point.