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 Cu 2+ and the superhyperfine parameters A || ′ and A ⊥ ′ of Ga 3+ ) for LaSrGa 0.995 Cu 0.005 O 4 crystal are systematically investigated on the basis of the perturbation calculations for these quantities of a tetragonally elongated octahedral 3d 9 complex. Arising from the Jahn–Teller effect, the impurity Cu 2+ center indicates the slightly larger relative tetragonal elongation ratio (≈4.0(1)%) than that (≈3.40(4)%) of the host Ga 3+ 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 Ga 3+ are theoretically studied for the first time. The unusual superhyperfine anisotropy ( A || ′< A ⊥ ′) for the present Ga 3+ ligand with respect to the conventional rule ( A || ′> A ⊥ ′) for the common anion ligands is ascribed to the opposite signs of the anisotropic terms for the [CuGa 4 ] 14+ cluster. The present studies reveal significant Cu 2+ –O 2− orbital hybridization and local tetragonal elongation around Cu 2+ , reflecting, to a certain extent, similar behaviors of the CuO 2 planes in oxide cuprates high T c superconductors. [ABSTRACT FROM AUTHOR]