MAGNETISM OF SINGLE NI IMPURITY IN HIGH-T-C CUPRATES

The magnetism of a single Ni impurity in high-T-c cuprates is discusse d on the basis of a generalized dp-model with the on-site Coulomb repu lsion among electrons on the 3d(x2-y2) and 3d(z2) orbitals of Ni as we ll as the Hund-rule coupling. It is shown that, for realistic values o f parameters, the effective spin moment of Ni impurity changes from si milar to 1 in lightly doped region to similar to 1/2 in the heavily do ped region, which is consistent with observations by NMR and magnetiza tion experiments.