Studies of the defect structures and g factors for two trigonal Ti3+ centers in LaMgAl11O19:Ti3+ crystal

Abstract

The defect models of two trigonal Ti3+ centers in the LaMgAl11O19:Ti3+ (LMA:Ti3+) crystal are resuggested as center 1 at the 2a site and center 3 at the 4f site. By using the crystal field parameters Dq based on the suggestion, the g factors g∥ and g⊥ for both Ti3+ centers are calculated from two microscopic spin-Hamiltonian theory methods, the complete diagonalization (of the energy matrix) method (CDM) and the perturbation theory method (PTM), based on the two spin-orbit (SO) parameter model (where both the contribution to spin-Hamiltonian parameters from the SO coupling parameter of the central 3dn ion and that of ligand ions are included). The calculated results from CMD and PTM are not only close to each other, but are also in agreement with the observed values. This suggests that (i) the present defect models of the two Ti3+ centers in the LMA:Ti3+ crystal are suitable and (ii) both CDM and PTM methods are effective to the explanations of spin-Hamiltonian parameters of 3d1 ions in crystals. The defect structures of both Ti3+ centers (which are quite different from the corresponding structures in the host LMA crystal, in particular, for center 1, the oxygen octahedron changes from the trigonal elongation in the host LMA crystal to the trigonal compression in the Ti3+ center) are also estimated from the calculations. The results are discussed.