INFLUENCE OF HYDROGEN ON 123-HTC AND 124-HTC SUPERCONDUCTORS STUDIED BY CU NMR AND NQR

The antiferromagnetic compounds produced by the reaction of the 123 an d 124 HTc superconductors with hydrogen are studied by nuclear resonan ce of copper. For the 123 compounds two reactions are possible, the re duction by hydrogen which leads to the normal antiferromagnetic YBa2Cu 3O6, and the solution of hydrogen in YBa2Cu3O7 which forms a different antiferromagnetic structure with hydrogen concentration of more than 2 H mol(-1). Both structures can be distinguished by the nuclear quadr upole resonance spectra of the Cu(1) sites and the nuclear magnetic re sonance spectra in the hyperfine field of the antiferromagnetic state. By using samples containing Gd at the place of Y we can prove that on ly the Cu(2) sites carry permanent magnetic moments. In the hydrogen l oaded YBa2Cu4O8 the situation is similar with the antiferromagnetic or der limited to the Cu(2) sites.