Paramagnetic Resonance Spectrum of Cobalt in Cerium Magnesium Nitrate at 4°K

Paramagnetic resonance spectra of cobalt in crystals containing cerium and bismuth magnesium nitrate have been studied at 4^∘{}K for various cerium-bismuth ratios. It is found that the cobalt hyperfine spectrum, well resolved in pure bismuth magnesium nitrate, is strongly attenuated by the addition of small percentages of cerium. For ionic cerium concentrations higher than 20% of the cerium-bismuth total, the cobalt hyperfine components cannot be resolved at all, except for the particular case of a 50% mixture. We attribute the attenuation of the cobalt spectrum to magnetic dipole interactions with the cerium ion, and suggest that this may also account for the fact that the observed degree of Gorter-Rose orientation of Co⁶⁰ in cerium magnesium nitrate disagrees with the results of calculations that do not include the effect of dipole-dipole interactions.