Low-Temperature Specific Heat Anomaly in Manganese Ferrites

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Abstract
The specific heats of a series of ferrites Mnx FeyO4 with x+y≈3, have been measured in the range 1.5°K to 6°K. The specific heats are anomalously large in this temperature range, and the anomaly increases with increasing manganese concentration. If the relatively small estimated lattice contribution is subtracted out, the resulting Cv vs T curves are concave downward, suggesting a Schottky‐type curve with a maximum in the range 7–10°K. Assuming that a valence transition, presumably involving manganese and iron atoms, is responsible for the specific heat anomaly, then the specific heat curves indicate that the temperature corresponding to the transition energy is in the range 18–25°K. An estimate of the amount of entropy involved indicates that the number of ion pairs involved in the transition is less than one‐tenth the number of MnFe2O4 molecules. This suggests that transitions involving manganese ions on octahedral sites alone could account for the specific heat anomaly.

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