Theoretical calculations of the spin-Hamiltonian parameters from a two-mechanism model for Cr5+ions in MVO3 (M = Li, Na, K, Rb) crystals

The spin-Hamiltonian parameters (g factors g//, g perpendicular to and hyperfine structure constants A//, A perpendicular to) of the approximately-tetragonal Cr5+ centers in MVO3 (M = Li, Na, K, Rb) crystals are calculated from the complete high-order perturbation formulas for d1 ions in tetragonal symmetry with the ground state [image omitted]. These formulas are based on a two-mechanism model, in which not only the contribution to spin-Hamiltonian parameters from the crystal-field (CF) mechanism concerning CF excitations, but also that from the charge-transfer (CT) mechanism concerning CT excitations (which is neglected in the widely-used CF theory) are included. The calculated results are in reasonable agreement with the experimental values and the signs of hyperfine structure constants are suggested. The calculations show that for a high valence state dn ion (e.g. Cr5+) in crystals, the exact calculation of spin-Hamiltonian parameters should take the contributions due to both CF and CT mechanisms into account.