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

A paramagnetic resonance spectrum of tetragonal symmetry due to ${\mathrm{Mn}}^{4+}$ ions in MgO has been observed. The spin-Hamiltonian parameters are $g_{\mathrm{II}}=1.9931\mathrm{}\pm 0.0002$, $g_{\perp }=1.9940\mathrm{}\pm 0.0002$, $A_{\mathrm{II}}=(-71.1\mathrm{}\pm 0.2)\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $A_{\perp }=(-70.6\mathrm{}\pm 0.1)\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, and $D=(-528.7\mathrm{}\pm 0.7)\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$. 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-${\mathrm{Mn}}^{2+}$-0-[=], where only deviations from the normal lattice charge are shown. The spectrum from octahedrally coordinated ${\mathrm{Mn}}^{4+}$ ions has been observed in a powder sample of MgO; here the spin-Hamiltonian parameters are $g=1.9941\mathrm{}\pm 0.0002$ and $A=-(70.82\mathrm{}\pm 0.10)\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$. The hyperfine fields at the nuclei of the $3d^3$ ions ${\mathrm{V}}^{2+}$, ${\mathrm{Cr}}^{3+}$, and ${\mathrm{Mn}}^{4+}$ in MgO are found to be almost identical.