Studies of the EPR Parameters gi and Ai for Co2+ in the Octahedral Sites of Y3Al5O12 and Y3Ga5O12 Crystals

Abstract

The perturbation formulas of EPR g factors g∥, g⟂ and hyperfine structure constants A∥, A⟂ for the trigonal octahedral 3d7 cluster are derived considering not only the configuration interaction effect due to the admixture among ground and excited states, but also the covalency effect due to the admixture between the d electrons of the 3d7 ion and the p electrons of ligands. In these formulas, the parameters related to both effects and the trigonal field parameters are estimated from the optical spectra and the structural parameters of the studied system. According to these formulas, the EPR parameters g∥, g⟂, A∥ and A⟂ for Co2+ in the octahedral sites of Y3Al5O12 and Y3Ga5O12 garnets are satisfactorily explained from the optical spectra and the structure data. The role of the covalency effect is discussed.