Electron Paramagnetic Resonance of Tetravalent Manganese Ions at Tetragonal and Octahedral Sites in MgO

A paramagnetic resonance spectrum of tetragonal symmetry due to Mn⁴⁺ ions in MgO has been observed. The spin-Hamiltonian parameters are gII=1.9931±0.0002, g_⊥=1.9940±0.0002, AII=(-71.1±0.2)×10^-4 cm^-1, A_⊥=(-70.6±0.1)×10^-4 cm^-1, and D=(-528.7±0.7)×10^-4 cm^-1. The departure from octahedral symmetry is attributed to the presence of a positive-ion vacancy at the first cation site on the tetragonal axis, thus forming the arrangement 0-Mn²⁺-0-[=], where only deviations from the normal lattice charge are shown. The spectrum from octahedrally coordinated Mn⁴⁺ ions has been observed in a powder sample of MgO; here the spin-Hamiltonian parameters are g=1.9941±0.0002 and A=-(70.82±0.10)×10^-4 cm^-1. The hyperfine fields at the nuclei of the 3d³ ions V²⁺, Cr³⁺, and Mn⁴⁺ in MgO are found to be almost identical.