Paramagnetic Resonance Linewidths in Some Rare-Earth Double Nitrates

We have measured the paramagnetic resonance linewidth δH at microwave frequencies for the three trivalent rare-earth ions Ce, Nd, and Sm present in small concentrations in La₂{Mg}₃(NO₃)₁₂·{}24H₂O. The linewidths appear to be strongly dependent upon the angle θ between the c axis of the crystal and the magnetic field, and in most cases the observed linewidths seem to be reasonably well explained by a simple theory which assumes a spatial distribution of paramagnetic resonance g values throughout the crystal.