In-plane anisotropy of the magnetic fluctuations in NaxCoO2·yH2ONaxCoO2·yH2O

We found two components of the in-plane Co59 NMR Knight shift K   and different nuclear spin–lattice relaxation rates 1/T11/T1 in bilayer hydrated superconductor NaxCoO2·yH2ONaxCoO2·yH2O, an oriented powder sample by a magnetic field in Fluorinert FC70. Distinguishable two peaks in the central transition line of the Co59 NMR spectrum at 10 K can be explained by an anisotropic Knight shift in a triangular plane. The hyperfine coupling constants seem to change around 150 K, in which the bulk susceptibility χχ shows a broad minimum, suggesting a change of the electronic state in the CoO2CoO2 plane.