Investigations on the spin Hamiltonian parameters for Gd3+ in YBa2Cu3O6+x

The spin Hamiltonian parameters [zero-field splittings (ZFSs) b20, b22, b40, b44, b60, b64 and the g factors] for the orthorhombic Gd3+ center in YBa2Cu3O6+x are theoretically investigated from the superposition model formulas for the ZFSs and the approximation formula of the g factors including admixture of the ground 8S7/2 and the excited 6L7/2 (L = P, D, F, G) states via the spin-orbit coupling interactions, respectively. The large anisotropy of the g factors in the (a, b) plane, originated from the anisotropy of spin susceptibility, is illustrated by the effective spin-orbit coupling coefficients ζ′ in the a and b principle axis directions. The calculated ZFSs and the g factors show reasonable agreement with the observed values.