Temperature Variation of the Magnetic Susceptibility, Gyromagnetic Ratio, and Heat Capacity inSm+++andEu+++

Abstract

Calculations of the magnetic susceptibilities in ${\mathrm{Sm}}^{+++}$ and ${\mathrm{Eu}}^{+++}$ inclusive of second order Zeeman terms, previously made at $T=300\mathrm{}°$K only, are extended to include values over a temperature range 0°K-800°K. The value assigned to the screening constant used in computing the multiplet intervals is adjusted to make the theoretical susceptibilities agree as closely as possible with experimental data. This fixes the separation between the lowest two levels with less uncertainty than in existing spectroscopic estimates. The computations show that ${\mathrm{Sm}}^{+++}$ should exhibit an unusual behavior in that, whereas at low temperatures the susceptibility decreases rapidly with increasing temperature, a minimum is reached between 375°K and 450°K. The theoretical values of the temperature coefficients of susceptibility in ${\mathrm{Sm}}^{+++}$ and ${\mathrm{Eu}}^{+++}$ (both of which are much lower than the Curie value $\frac{1}{T}$) are in satisfactory agreement with experiment when the second order Zeeman terms are included. The other elements in the rare earth group do not deviate appreciably from the Curie law. The present computations show an increase in the gyromagnetic ratio in ${\mathrm{Sm}}^{+++}$ with increasing temperature, in contrast with the behavior in ${\mathrm{Eu}}^{+++}$ in which increasing temperature decreases this ratio. The temperature variation of the contribution of the multiplet levels to the heat capacity of ${\mathrm{Sm}}^{+++}$ and ${\mathrm{Eu}}^{+++}$ is also calculated.