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| The complete third-order perturbation formulas of g factors g// and g^ for 3d2 ions in tetragonal MX4 clusters have been established from a cluster approach. In these formulas, in addition to the contributions to g factors from the crystal-field mechanism in the crystal-field theory, the contributions from the charge-transfer mechanism are included. From these formulas, the g factors g// and g^ for Cr4+ ion in Bi4Ge3O12 crystal are calculated. The results are in agreement with the observed values. The calculated Dgi (i=// or ^) due to the charge-transfer mechanism is opposite in sign and about 20% in magnitude, compared with that due to the crystal-field mechanism. So, for the 3dn ions having high valence state in crystals, the reasonable explanations of g factors should take both the crystal-field and charge-transfer mechanisms into account. |
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| Keywords:Electron Paramagnetic Resonance, Crystal- and Ligand- field Theory, Charge-Transfer mechanism, Cr4+, Bi4Ge3O12. |
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