The quantitative relationship between the spin Hamiltonian parameters (D, g||, Δg) and the crystal structure parameters for the Cr3+−VZn tetragonal defect centre in a Cr3+:KZnF3 crystal was established by using the superposition model. On the above basis, the local structure distortion and the spin Hamiltonian parameter for the Cr3+−VZn tetragonal defect centre in the KZnF3 crystal were systematically investigated using the complete diagonalization method. It was found that the VZn vacancy and the differences in mass, radius and charge between the Cr3+ and the Zn2+ ions induce the local lattice distortion of the Cr3+ centre ions in the KZnF3 crystal. The local lattice distortion was shown to give rise to the tetragonal crystal field, which in turn results in the tetragonal zero-field splitting parameter D and the anisotropic g factor Δg. It was found that the ligand F− ion along [001] and the other five F− ions move towards the central Cr3+ by distances of Δ1 = 0.0121nm and Δ2 = 0.0026nm, respectively. The approach took account of the spin—orbit interaction as well as the spin—spin, spin—other-orbit, and orbit—orbit interactions omitted in the previous studies. It was found that for the Cr3+ ions in the Cr3+:KZnF3 crystal, although the spin—orbit mechanism was the most important one, the contribution to the spin Hamiltonian parameters from the other three mechanisms, including spin—spin, spin—other-orbit, and orbit—orbit magnetic interactions, was appreciable and should not be omitted, especially for the zero-field splitting (ZFS) parameter D.

Local Structure Distortion and Spin Hamiltonian Parameters for Cr3+−VZn Tetragonal Defect Centre in Cr3+ Doped KZnF3 Crystal. Z.Y.Yang: Chinese Physics B, 2011, 20[9], 097601