Investigations of the Spin-Hamiltonian Parameters for the Rhombic Mo5+ Centers in Ca1−xYxMoO4 Crystal

The spin-Hamiltonian parameters (g factors gi and hyperfine structure constants Ai, where i = x, y, z) of the rhombic Mo5+ center in Ca1−xYxMoO4 crystal are calculated from the high-order perturbation formulas based on the two-mechanism model for the rhombic d1 tetrahedral clusters with the ground state |dz2〉. In these formulas, besides the contributions due to the widely applied crystal-field (CF) mechanism concerning CF excited states, those due to the charge-transfer (CT) mechanism (which is omitted in CF theory) concerning CT excited states are considered. The calculated results are in reasonable agreement with the experimental values. The calculations show that because of the great relative importance of CT mechanism for the components of spin-Hamiltonian parameter along x and y axes, the accurate and complete calculations of spin-Hamiltonian parameters for Mo5+ and other high valence state dn ions in crystals should take account of both the CF and CT mechanisms. The defect model of the rhombic Mo5+ center is also confirmed from the calculations.