The Effect of Crystalline Fields on the Magnetic Susceptibilities of Sm+++ and Eu+++, and the Heat Capacity of Sm+++

Abstract

The temperature variation of the paramagnetic susceptibility of ${\mathrm{Sm}}^{+++}$ is calculated on the assumption that the ion is subject to a crystalline field which can be represented by the potential $V=\Sigma \stackrel{}{i}\left[D\right({x_i}^4+{y_i}^4+{z_i}^4)+A{x_i}^2+B{y_i}^2-(A+B\left)\mathrm{}{z_i}^2\right],$ the cubic portion of this potential predominant. The susceptibility is decreased by about 25 percent with respect to that of the free ion at 74°K when the cubic potential is so chosen as to give a separation of the $J=\frac{5}{2}$ levels of about 200 ${\mathrm{cm}}^{-1\mathrm{}}$ which is of the order indicated by Spedding's work on the absorption spectrum of samarium compounds. The theoretical values of the susceptibility are then in satisfactory agreement with the experimental data of Freed over a temperature range from 74°K to room temperature. The rhombic portion of the field separates the lowest excited level into two but the contribution to the susceptibility is negligible if the rhombic separation is small compared with the cubic separation. In striking contrast with ${\mathrm{Sm}}^{+++}$, Eu behaves like the free ion even in the presence of a crystalline field. The contribution to the heat capacity of ${\mathrm{Sm}}^{+++}$ at various temperatures due to the excited levels is computed. When the levels which give good agreement with susceptibility data are used, the general shape of the curve is the same as that obtained experimentally by Ahlberg and Freed but the theoretical values are consistently lower than the experimental values.