NMR-STUDIES OF THE ELECTRONIC AND MAGNETIC-PROPERTIES OF HIGH-TC MATERIALS

In the insulating state of cuprates, NMR techniques allow investigations of the influence of hole doping or impurity substitutions on the 3D AF ordering. In the metallic state of YBa2Cu3O6+x, NMR shift data taken on the various nuclear sites. Y-89, O-17 and Cu-63 have allowed to conclude that the covalency between Cu(3d(x2-y2)) and O(2p-sigma) holes results in a spin system which behaves as a single spin fluid. The large decrease of the susceptibility of the CuO2 planes at low T for oxygen depleted samples, as well as the different T dependences of the Y-89, O-17 and Cu-63 relaxation rates is attributed to the existence of AF correlations at the wave vector Q of the AF structure of YBa2Cu3O6. However, the Y-89 and O-17 relaxation rates, which filter the Q component of the dynamic susceptibility, exhibit a behaviour similar to that of a Fermi liquid, for high-T(c) samples. The T variations of the spin susceptibility and of the AF correlations are discussed.