The thermal and magnetic properties of chromium potassium alum below 0·1 °K

Abstract
An account is given of a determination of the entropy and absolute temperature as a function of ‘magnetic temperature’ (i. e. the reciprocal of susceptibility) for chromium potassium alum in the temperature range 0·007 to 0·1°K. The Curie point, which is characterized by a λ-anomaly in the specific heat, and a maximum in the susceptibility, is found to be at 0·011°K for this substance. The results are discussed in the light of other previously published and contradictory measurements on this substance. A theoretical treatment of the influence of the crystalline electric field on the entropy of magnetization is given in an appendix.