Thermophysical measurements on transition-metal tungstates III. Heat capacity of antiferromagnetic manganese tungstate

Three anomalies were found during measurements of the heat capacity of manganese tungstate from 4 to 350 K by adiabatic calorimetry; a small peak at (6.8 +/- 0.1) K, and two large sharp peaks at (12.57 +/- 0.05) K and (13.36 +/- 0.05) K. The excess entropy associated with the antiferromagnetic transition was estimated by means of calculations which utilized the heat capacity of zinc tungstate to approximate contributions from lattice vibrations and was found in good accord with the value R ln6. The results between 5 and 11.5 K obey a power law: Cmag = AT1.73. The double anomaly is discussed in terms of the super-exchange properties of MnWO4. Selected thermal functions, Cpo, So, and -{Go(T) - Ho(0)}/T are respectively 27.40, 31.66, and 16.10 calth K-1 mol-1 at T = 298.15 K.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/21919/1/0000326.pd