Investigations on the defect structure and the spin Hamiltonian parameters for LaSrGa0.995Cu0.005O4 crystal

The defect structure and the spin Hamiltonian parameters (g factors g||, g⊥, the hyperfine structure constants A|| and A⊥ of Cu2+ and the superhyperfine parameters A||′ and A⊥′ of Ga3+) for LaSrGa0.995Cu0.005O4 crystal are systematically investigated on the basis of the perturbation calculations for these quantities of a tetragonally elongated octahedral 3d9 complex. Arising from the Jahn-Teller effect, the impurity Cu2+ center indicates the slightly larger relative tetragonal elongation ratio (≈4.0(1)%) than that (≈3.40(4)%) of the host Ga3+ site. The computed values of the spin Hamiltonian parameters agree well with the measured results. To the best of our knowledge, the superhyperfine parameters of Ga3+ are theoretically studied for the first time. The unusual superhyperfine anisotropy (A||′A⊥′) for the common anion ligands is ascribed to the opposite signs of the anisotropic terms for the [CuGa4]14+ cluster. The present studies reveal significant Cu2+-O2− orbital hybridization and local tetragonal elongation around Cu2+, reflecting, to a certain extent, similar behaviors of the CuO2 planes in oxide cuprates high Tc superconductors.