Magnetism of single Ni impurity in high-T-c cuprates

The magnetism of a single Ni impurity in high-T-c cuprates is discussed on the basis of a generalized dp-model with the on-site Coulomb repulsion among electrons on the 3d(x2-y2) and 3d(z2) orbitals of Ni as well as the Hund-rule coupling. It is shown that, for realistic values of parameters, the effective spin moment of Ni impurity changes from similar to 1 in lightly doped region to similar to 1/2 in the heavily doped region, which is consistent with observations by NMR and magnetization experiments.