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.