EPR studies of Mo3+ ion in single crystals of NH4Al(SO4)2⋅12H2O

Electron paramagnetic resonance studies of Mo3+ ion in NH4Al(SO4)2⋅12H2O single crystals are made at X-band frequencies and at room temperature. It is found that there are four magnetically inequivalent complexes of Mo3+ ion in the lattice which exhibit tirgonal symmetry. The angular variation of the fine structure lines is studied in the crystallographic (111) and (100) planes. The z axes of the complexes are found to be along the (111) directions. The spectra are analyzed using the fine structure spin-Hamiltonian and the parameters are found to be g∥=1.974, g⊥=2.009, and D=506.8×10−4 cm−1. Paramagnetic resonance of the polycrystalline samples is also studied and the usual spin-Hamiltonian analysis is made. A model is proposed for the position of the Mo3+ ion in the lattice of ammonium alum.