Magnetic Susceptibility and Crystalline Field Levels of Ytterbium Gallium Garnet

The paramagnetic susceptibility of YbGaG is measured over the interval 4-1000°K, primarily in order to obtain information on the location of the ${\Gamma }_6$ level, which, unlike ${\Gamma }_8$, does not combine magnetically with the ground ${\Gamma }_7$ state, and so is not detectable in the usual magnetic experiments at low temperatures. From our measurements it is inferred that the ${\Gamma }_6$ level is about 800 ${\mathrm{cm}}^{-1\mathrm{}}$ above ${\Gamma }_7$. High precision cannot be claimed for this estimate, as our analysis of the magnetic data is made on the assumption of a perfectly cubic crystalline field, whereas the local symmetry at an individual lattice site is known to be but approximately cubic. In any case, the conclusion seems warranted that any low-lying levels at 100 ${\mathrm{cm}}^{-1\mathrm{}}$ or so deduced from optical absorption data are of a vibrational rather than electronic nature.