ESR study of Fe 3+ and Mn 2+ ions on trigonal sites in ilmenite structure MgTiO 3

Abstract

Electron spin resonance has been observed for Fe 3+ and Mn 2+ ions occupying sites with trigonal symmetry in undoped and doped Verneuil-grown crystals of the ilmenite type compound MgTiO 3. At 300 K, the fine structure parameters in the spin Hamiltonian are (in 10 −4cm −1) D = +844 (± 1), ( a− F) = +118 (± 1), a = 69 (± 7) for Fe 3+ and D = +164 (± 1), ( a − F) = +10.2 (± l), a = 7.0 (± 1) for Mn 2+. These values are compared with literature data for Fe 3+ and Mn 2+ in other oxides, especially Al 2o 3, with particular reference to the recent “superposition” theory of the effect of a trigonal distortion. From the orientation of the axes of cubic pseudosymmetry of the spin Hamiltonian, and with the assumption that a has the same sign for both ions, it is proposed that Fe 3+ and Mn 2+ occupy the same octahedral site, namely the Mg 2+ site. Anomalous line splittings observed for one sample were attributed to twinning on (0001) or {1120} planes.