Paramagnetic resonance and hyperfine structure in four cobalt salts

Abstract

The paramagnetic resonance spectra of cobalt ammonium sulphate, cobalt potassium sulphate, cobalt fluosilicate and cobalt sulphate, each diluted with the isomorphous zinc salt, have been analyzed. These salts exhibit great anisotropy both in the g-values (spectroscopic splitting factor) and the hyperfine structure. The results show that the ground state of the cobalt ion is an electronic doublet, and confirm the nuclear spin of $^{59}$Co as $\frac{7}{2}$. The theoretical interpretation of the results by crystalline field theory has been carried out by Abragam & Pryce (1951 a). The contribution to the specific heat from the hyperfine structure is computed for each salt. In addition, the measurements of the specific heat and susceptibility of cobalt sulphate by Fritz & Giauque (1949) are given a new interpretation consistent with that of other cobalt salts. This requires that the magnetic entropy of cobalt sulphate be taken as R log$_{e}$ 2, instead of R log$_{e}$ 4, as assumed by Fritz & Giauque.