材料期刊网

The EPR parameters g factors and the superhyperfine parameters for the tetrahedral [FeX4](-) clusters in AgX (X = Cl, Br) are theoretically investigated from the perturbation formulas of these parameters for a 3d(5) ion under tetrahedra by considering both the crystal-field and charge transfer contributions. The related model parameters are quantitatively determined from the cluster approach in a uniform way. The g-shift Delta g (= g-g(s), where g(s) approximate to 2.0023 is the spin only value) from the charge transfer contribution is opposite (positive) in sign and much larger in magnitude as compared with that from the crystal-field one. The importance of the charge transfer contribution increases rapidly with increasing the covalency and the spin-orbit coupling coefficient of the ligand and thus exhibits the order of AgCl < AgBr. The unpaired spin densities of the halogen ns, np sigma and np pi orbitals are quantitatively determined from the related molecular orbital coefficients based on the cluster approach.