Magnetic Susceptibility of Cerous Magnesium Nitrate

The most striking features of the behavior of cerous magnesium nitrate at liquid helium temperatures—extremely anisotropic susceptibility with $g_{\mathrm{II}}\approx 0$, a large temperature-independent term in ${\chi }_{\perp }$, the spin-lattice relaxation time varying as the twelfth or higher power of $T$ in the region of 2°K—have until very recently received no detailed explanation. A measurement of ${\chi }_{\perp }$ between 4° and 300°K was undertaken to elicit information on the energies of the excited doublets within the $J=\frac{5}{2}$ ground multiplet, and thus to provide a guide for the reassessment of the crystal field parameters. We find ${\delta }_1$ and ${\delta }_2$ to be 30 and (roughly) 200 ${\mathrm{cm}}^{-1\mathrm{}}$, respectively, in contrast to the 113 and 150 ${\mathrm{cm}}^{-1\mathrm{}}$ of existing theory. The results are at variance with the published data for ${\chi }_{\perp }$ above 85°K, but are in fairly good agreement with the recent findings of Leask and Wolf at low temperatures.