Magnetic and Thermal Properties of Crystalline Copper Sulphate at Low Temperatures

Abstract

THE principal magnetic susceptibilities of crystalline copper sulphate (CuSO₄.5H₂O) have been measured from room temperature down to about 90° K.¹. From a detailed analysis of these magnetic data, Jordahl² finds that they can be explained quantitatively on the assumption that the crystalline electric field in the neighbourhood of the Cu^{+ +} ion in the crystal is predominantly cubic in symmetry, with a small tetragonal component superposed on it. The ground state of the Cu^{+ +} ion is²D, and the crystalline field postulated is such that under the influence of its cubic part the energy levels split up into two sets, the lower set having a two-fold orbital degeneracy, and the upper a three-fold one, the separation between the two sets being about 18,300 cm.^-1; the tetragonal part of the field separates the levels of either set by about 2,550 cm.^-1. Each of these separated levels will have a two-fold spin degeneracy, which, being of the Kramers type, will not be removed by the crystalline field.