Using the Hubbard Hamiltonian for the CuOz planes, we calculate the static spin susceptibility x(T) in the paramagnetic phase. For small hole doping x(T) is suppressed at low temperatures due to antiferromagnetic correlations between local magnetic moments at the Cu sites. For intermediate hole doping (x = 0.25) we find that x(T) increases with decreasing temperature. For x > 0.4 the magnetic moments disappear and we obtain a temperatureindependent Pauli susceptibility. As far as the Knight-shift data are concerned, our theory yields that due to Cu-0 spin singlet formation one spin degree of freedom determines the magnetic response of all nuclei.

Using a three-band Hubbard Hamiltonian within a slave-boson mean-field approximation we determine the doping dependence of the density of states in the Cu02 planes. We analyze in detail the occurrence of local magnetic moments, their efFects on the electronic structure, and the insulating state resulting from a charge transfer or a Mott-Hubbard gap. This theory permits a treatment of highly correlated systems over the whole doping range and thus of the transition from local moment to fully itinerant behavior. Using the density of states various magnetic, spectroscopic, and transport properties are calculated. Our analysis sheds light on the difference of electron versus hole doping and in particular on the doping dependence of the Cu-0 singlet and the Hall coeKcient.More generally, by comparing with experimental data and theoretical results obtained by alternative methods one learns more about the validity of the slave-boson mean-field theory. We also discuss how the theory can be extended to include quantum Auctuations.

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