59Co-NMR Knight Shift of Aligned Crystals and Polycrystalline Samples of Superconducting Na0.3CoO2.1.3H2O

Temperature (T) dependence of 59Co-NMR Knight shifts K of Na0.3CoO2.1.3H2O has been studied, where samples of randomly oriented powder and aligned crystals have been used for the applied magnetic fields H // ab plane and H //c-axis, respectively. For both directions of H, the shift K decreases below the superconducting transition temperature Tc(H) with decreasing T, indicating that the superconducting electron pairs are in the singlet state. The upper critical fields Hc2(T) determined from the K(H)-T curves are found to be consistent with the values reported by the resistivity measurements for both directions of H.