Specific Heat of Copper Sulphate below 1° K

Abstract

IT is well known that cæsium titanium alum exhibits no specific heat anomaly due to Stark splitting, but only a large increase at very low temperatures attributed to magnetic interaction between the ions. This is explained by the well-supported hypothesis that the orbital momentum is quenched, leaving the ion effectively in an ²S state since it possesses only one electron spin, and Kramers has shown that the ²S state is remarkably free from splitting due to the lattice field. The cupric ion would be expected to behave similarly, since susceptibility measurements show that the orbital momentum is largely quenched and since there is only one electron spin.