Theoretical investigations of the local structure and the EPR parameters for the trigonal Co ^{2+} center in K _{4}CdCl _{6}
Abstract
The local structure and the electron paramagnetic resonance (EPR) g factors g_{}, g_{⊥} and the hyperfine structure constants A_{} and A_{⊥} for the trigonal Co ^{2+} center in K _{4}CdCl _{6} are theoretically investigated by using the perturbation formulas of the EPR parameters for a 3d ^{7} ion in trigonal symmetry based on the cluster approach. In these formulas, the contributions to the EPR parameters arising from the admixture of different energy levels, covalency effect and low symmetry distortion are included. The parameters related to the above effects are obtained from the optical spectral data and the local geometrical relationship of the studied system. By analyzing the EPR spectra, we find that the impurityligand bonding angle β (≈53.54°) related to the C_{3}axis in the Co ^{2+} impurity center is smaller than the corresponding metalligand bonding angle β_{H} (≈54.90°) in the host K _{4}CdCl _{6}. From the difference ∆ β between the bonding angle β (or β_{H}) and the corresponding angle β_{0} (≈54.74°) in cubic symmetry, the chlorine octahedron changes from compression (∆ β_{H}= β_{H} β_{0}>0) in the host to elongation (∆ β= β β_{0}<0) in the impurity center. The calculated EPR parameters, especially the anisotropies of the g and A factors for K _{4}CdCl _{6}:Co ^{2+} based on the angle β show good agreement with the observed data. The theoretical studies on the local structure for Co ^{2+} in K _{4}CdCl _{6} would be helpful to understand the structure properties for the equivalent octahedral transitionmetal M site in the isostructural A _{3}M'MO _{6} compounds.
 Publication:

Journal of Magnetism and Magnetic Materials
 Pub Date:
 August 2004
 DOI:
 10.1016/j.jmmm.2004.01.039
 Bibcode:
 2004JMMM..279...14W