Paramagnetic Resonance Spectra off3Ions in a Cubic Site

The paramagnetic resonance spectra of ${\mathrm{Nd}}^{3+}$ and ${\mathrm{U}}^{3+}$ in the cubic field of Ca${\mathrm{F}}_2$ have been investigated at 3 cm at 20°K. In the case of ${\mathrm{Nd}}^{3+}$ transitions within the lowest quartet ${{\Gamma }_8}^{\mathrm{}\left(2\right)\mathrm{}}$ and possibly in the next higher quartet ${{\Gamma }_8}^{\mathrm{}\left(1\right)\mathrm{}}$ have been observed. The angular behavior conforms with that predicted by Bleaney's formulism of the spin Hamiltonian of a ${\Gamma }_8$ state. In the case of ${\mathrm{U}}^{3+}$ there are considerable deviations of the experimental $g$ values from the calculated ones. It is suggested that these deviations are caused by the stronger cubic field.