The Ground State Splitting of Gadolinium Sulphate Octohydrate

The zero-field paramagnetic resonance frequencies of Gd 3+ diluted in the sulphate octohydrates of yttrium, samarium and neodymium have been measured directly at 4.2°, 80° and 273 °K. The spin Hamiltonian is of the predominantly axial type and the energy levels inferred for pure gadolinium sulphate at 4 °K are (in deg K): 0 ( S z = ±1/2), 0.320 (±3/2), 0.710 (±5/2) and 1.257 (±7/2). Gd 3+ in samarium sulphate is promising for a zero-field maser with an amplifying band extending from 7.8 to 8.5 Gc/s. The spin Hamiltonian deduced from traditional paramagnetic resonance is shown in one case to be reliable to within ±3% for predicting zero-field frequencies.