59Co-NMR knight shift of aligned crystals and polycrystalline samples of superconducting Na0.3CoO2•1.3H2O

The temperature (T) dependence of the Co-59-NMR Knight shifts K of Na0.3CoO2 center dot 1.3H(2)O has been studied, where samples of randomly oriented powder and aligned crystals have been used for the applied magnetic fields H parallel to ab plane and H parallel to c-axis, respectively. For both directions of H, the shift K decreases below the superconducting transition temperature T-c(H) with decreasing T, indicating that the superconducting electron pairs are in the singlet state. The upper critical fields H-c2(T) determined from the K(H)-T curves are found to be consistent with the values reported from the resistivity measurements for both directions of H.