Spin-Spin Interactions in Cerium Ethyl Sulfate

The spin-spin interactions in cerium ethyl sulfate have been investigated by the method of paramagnetic-resonance line moments under the condition of appreciable spin alignment by the Zeeman interaction, i.e., $h\nu >\mathrm{kT}$. The total nondipolar interaction of a cerium ion with all its neighbors was found to be antiferromagnetic, having the magnitude (0.113±0.003)${\mathrm{cm}}^{-1\mathrm{}}$. As previously assumed, this interaction has been ascribed to the electric quadrupole-quadrupole coupling of the $4f$ electrons of neighboring ions. The lack of agreement between the measurements and theory is attributed to the sensitivity of the calculations to parameters not sufficiently well known for the Ce ion in the ethyl-sulfate lattice. Several unusual qualitative features of the resonance spectrum are explainable on the basis of a $\mathrm{qq}$ coupling between ions. In addition, the observation of the resonance spectra of various other rare-earth ions in cerium ethyl sulfate has permitted a measurement of the following nearest-neighbor nondipolar interactions in the ethyl sulfates: Ce-Pr: (0.32±0.06)×${10}^{-2\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$; Ce-Nd: (1.2±0.2)×${10}^{-2\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$; Ce-Gd: (0.00±0.05)×${10}^{-2\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$.