Heat Capacity and Entropy of FeF2 and CoF2 from 11 to 300°K. Thermal Anomalies Associated with Antiferromagnetic Ordering

Abstract

The heat capacities of FeF2 and CoF2 have been measured between 11 and 300°K. Both salts show anomalies in heat capacity associated with the antiferromagnetic ordering of the magnetic ions. The heat capacity of FeF2 exhibits a sharp maximum of 17.8 cal deg—1 mole—1 at 78.35°K and that of CoF2 has a maximum of 5.64 cal deg—1 mole—1 at 37.70°K. Values of the heat capacity, entropy, enthalpy, and free energy are tabulated at selected temperatures. The values of the entropy and enthalpy at 298.16°K are: FeF2, S0=20.79±0.04 cal deg—1 mole—1, H0–H00=3049±6 cal mole—1; CoF2, S0=19.59±0.04 cal deg—1 mole—1, H0–H00=2978±6 cal mole—1.