Theoretical study of effective magnetic interactions in high-Tc Cu oxides

Starting from a two-band Hubbard model for cupric oxides and using perturbation theory, we study the effect of a small O-O hopping term tp on the parameters of the single-band t-J model. It is found that as long as the wave function on the oxygen site is extended and Bloch-like, the antiferromagnetic coupling between the nearest-neighbor copper spins decreases rapidly with increasing hole doping. This behavior seems to be insensitive to the value of tp and dispersion of the oxygen band, and is consistent with the results of recent experiments. We also show that between next-nearest-neighbor copper spins, there exists a non-negligible antiferromagnetic coupling even in the zero-doping limit.