NQR AND NMR STUDIES OF YBa2Cu3Ox(6.0 ≦ x ≦ 6.91)

Nuclear Quadrupole Resonance (NQR) and Nuclear Magnetic Resonance (NMR) have been utilized to investigate the 90 K class superconductor YBa 2 Cu 3 O 6.91 and relevant oxides YBa 2 Cu 3 O x (6.0 ≦ x ≦ 6.91). Two 63 Cu NQR lines have been observed at about 31 MHz and 22 MHz for x = 6.91, which were proved to be from the Cu2 and Cu1 sites respectively using the NMR technique for an oriented sample. The spin-lattice relaxation time T 1 exhibits anomalous temperature dependence with high relaxation rate in the normal state. Power-law like temperature dependence was observed well below T c for the Cu2 sites. The former indicates the strong influence of Cu spin fluctuations, while the latter may be understood as the realization of the anisotropic superconductivity. Antiferromagnetic nuclear resonance has been obtained for x = 6.0 yielding a clear evidence of magnetic ordering in the Cu2-O 2 planes. This is consistent with neutron scattering and μ SR studies.