Local structure distortion and spin Hamiltonian parameters for Cr3+-VZn tetragonal defect centre in Cr3+ doped KZnF3 crystal

The quantitative relationship between the spin Hamiltonian parameters (D,g‖,Δg) and the crystal structure parameters for the Cr 3+-V Zn tetragonal defect centre in a Cr 3+:KZnF 3 crystal is established by using the superposition model.On the above basis,the local structure distortion and the spin Hamiltonian parameter for the Cr 3+-V Zn tetragonal defect centre in the KZnF 3 crystal are systematically investigated using the complete diagonalization method.It is found that the V Zn vacancy and the differences in mass,radius and charge between the Cr 3+ and the Zn 2+ ions induce the local lattice distortion of the Cr 3+ centre ions in the KZnF 3 crystal.The local lattice distortion is 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.We find that the ligand F-ion along [001] and the other five F-ions move towards the central Cr 3+ by distances of Δ1=0.0121 nm and Δ2=0.0026 nm,respectively.Our approach takes into account the spin-orbit interaction as well as the spin-spin,spin-other-orbit,and orbit-orbit interactions omitted in the previous studies.It is found that for the Cr 3+ ions in the Cr 3+:KZnF 3 crystal,although the spin-orbit mechanism is 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,is appreciable and should not be omitted,especially for the zero-field splitting (ZFS) parameter D.