Investigations on the g factors for the Cu2+ sites in YBa1.9Na0.1Cu3O7-δ and YBa2Cu3O7-δ

The anisotropic g factors g(i) (i=x, y, z) for the six-fold coordinated orthorhombic Cu2+(1) site in YBai(1.9)Na(0.1)Cu(3)O(7- delta) and the five-fold coordinated tetragonal Cu2+(2) site in YBa2Cu3O7-delta are theoretically studied from the perturbation formulas of the g factors for a 3d(9) ion in orthorhombically and tetragonally elongated octahedra, respectively. The orthorhombic (or tetragonal) field parameters are obtained using the superposition model and the local structures of the Cu2+ sites. In view of covalency, the contributions from the ligand orbital and spin-orbit coupling interactions are taken into account. For the Cu2+(1) site in YBai(1.9)Na(0.1)Cu(3)O(7- delta), the axial anisotropy Delta g[=g(z)-(g(x)-gy)/2] may be ascribed to the moderate (about 3%) elongation of the Cu-O distance along c axis, while the perpendicular anisotropy delta g(=g(x)-g(y)) can be characterized by the planar bond length deviation difference delta R(approximate to 0.083 angstrom) in the perpendicular (ab) plane. However, for the Cu2+(2) site in YBa2Cu3O7-delta, the anisotropy Delta g(=g(parallel to) - g(perpendicular to)) is illustrated by the significant elongation of the [CuO5](8)- cluster along c axis with about 25% longer axial Cu-O distance than the four planar ones. The theoretical g factors are in good agreement with the experimental data. (C) 2012 Elsevier B.V. All rights reserved.