Studies on the EPR parameters for the interstitial tetragonal Co2+center in NH4I

The electron paramagnetic resonance (EPR) parameters (g factors g //, g ⊥ and the hyperfine structure constants) for the interstitial Co2+ center in NH4I are theoretically investigated by the diagonalization of the 6×6 energy matrix of the 4T1 ground state for a 3d7 ion under tetragonal symmetry. The contributions from the admixtures of various J (=1/2, 3/2, 5/2) states and the ligand orbital and spin–orbit coupling interactions, which were normally ignored in previous works, are taken into account in the present treatments. The contributions to the EPR parameters are discussed, and the discrepancies between the calculated hyperfine structure constants and the experimental data are also analyzed.