The paramagnetic resonance spectra of some rare-earth double nitrates

The paramagnetic resonance spectra of praseodymium magnesium nitrate, neodymium magnesium nitrate, and samarium magnesium nitrate have been analyzed using centimetre wave-lengths. The spectra were observable only on cooling the crystals to 4$\cdot $2 degrees K; at higher temperatures the spin-lattice relaxation times were so short as to broaden the lines beyond the possibility of detection. The spectroscopic splitting factors (g-values) and hyperfine structures exhibit great anisotropy. The values of the nuclear spins of $^{147}$Sm and $^{149}$Sm are both confirmed to be $\frac{7}{2}$. The magnetic susceptibility and the magnetic contributions to the specific heat are computed for each salt. In each case the nuclear hyperfine structure is responsible for the principal contribution to the specific heat.