Thermal and magnetic properties of ferric methylammonium sulphate

Abstract
The specific heat and magnetic susceptibility of ferric methylammonium sulphate have been measured at temperatures between 0·17 and 20°K. The specific heat has been analyzed into a lattice contribution and a magnetic anomaly. It is shown that the magnetic contribution to the specific heat can be accounted for almost entirely by the Schottky anomaly due to the Stark splittings of the ground state of the Fe 3+ ions, previously determined by Bleaney & Trenam. These splittings are unusually large in this salt, with the result that the specific heat is very large at temperatures near 1°K, reaching a maximum value of 1·1 cal/mole at 0·33°K. The salt should therefore be useful for magnetic cooling experiments in which other substances are to be kept below 1°K for prolonged periods.

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