Theoretical investigations of the spin Hamiltonian parameters and local structures for the tetragonal V3+ and Ti2+ centers in MgO and CaO

The spin Hamiltonian parameters (zero-field splitting D, g factor and hyperfine structure constant) and the local structures for MgO:V3+, CaO:V3+ and CaO:Ti2+ are theoretically investigated from the perturbation formulas of these parameters for 3d2 ions under tetragonally distorted octahedra. The contributions from the dynamical Jahn-Teller effect, the configuration interactions and the ligand orbital and spin-orbit coupling interactions are quantitatively taken into account based on the cluster approach in a uniform way. The ligand octahedra are found to suffer the relative elongations of about 1.5%, 4.4% and 4.6% for MgO:V3+, CaO:V3+ and CaO:Ti2+, respectively, along the C4 axis due to the dynamical Jahn-Teller effect. The calculated spin Hamiltonian parameters based on the above local tetragonal elongations show reasonable agreement with the experimental data for all the systems. The results are discussed.