Magnetic and Thermal Properties of Chromic Methylamine Alum Below 1°K

The earlier measurements of de Klerk and Hudson on a spherical mass of small crystals of chromic methylamine alum have been repeated, and extended, using a one-inch sphere ground from a large single crystal. The variation of susceptibility with entropy follows closely—down to 0.1°K—the predictions of the theory of Hebb and Purcell when a suitable choice is made for the value of $\delta$, the splitting between the two spin-doublets in the ground level of the ${\mathrm{Cr}}^{+++}$ ion. It is found that $\frac{\delta }{k}=0.269\mathrm{}\pm 0.003$ degree.