NMR studies of high temperature superconductors

Results of NMR experiments mostly in YBa2Cu4O7-δ are reviewed. The normal state data revealed two important aspects of the magnetic properties, namely, the temperature dependent antiferromagnetic Cu spin correlations and the spin gap behavior, the latter being observed in the reduced oxygen material. These features appear to be the general properties of many high Tc cuprates. The Cu nuclear relaxation behavior in the superconducting state show some anomalous feature which remains to be explained. © 1992.