Theoretical studies of the spin Hamiltonian parameters for the tetragonal Cu2+ centres in NaF and CsCdF3

The spin Hamiltonian parameters (g factors and hyperfine structure constants) for Cu2+ in NaF and CsCdF3 are theoretically studied using the high order perturbation formulas of these parameters for a 3d9 ion in a tetragonally elongated octahedron. The Cu2+ centres are found to suffer the relative elongation ratios of about 5.5% and 3.1% for Cu2+ in NaF and CsCdF3, respectively, along the C4 axis due to the Jahn–Teller effect. The theoretical results of the spin Hamiltonian parameters show good agreement with the experimental data. The larger g anisotropy for Cu2+ in NaF than CsCdF3 is attributed to the larger relative tetragonal elongation ratio arising from the longer distance and hence the weaker bonding (or lower force constant) in the former. The significant discrepancies in the hyperfine structure constants for the two systems are analysed in view of their different core polarization constants and the reduction factors H related to the local structures.