Co-NMR measurements on crystalline sample of the bilayere hydrate Nax(H3O)zCoO2•yH2O

Co-nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements were performed on a c-axis-aligned crystalline sample of cobaltate superconductor Na-x(H3O)(z)CoO2 center dot yH(2)O. The sample properties were characterized in detail by using the NMR and NQR measurements, and the sample was confirmed to exhibit a clear superconducting transition at T-c = 4.56 K. The external field direction was controlled by rotating the sample at low temperatures. The detailed analyses of the NMR spectra revealed that the c-axis direction of the crystalline sample was distributed within +/- 2.5 degrees. The relaxation rate divided by temperature 1/T1T and Knight shift were measured in the superconducting state. The Knight shift decreased by approximately 0.015% below T-c, which is almost one order smaller than those reported previously. The value of the decrease was the same order as the superconducting diamagnetic effect. The quantitative discussion is given to the Knight shift in the superconducting state.