23Na NMR evidence for charge order and anomalous magnetism in NaxCoO2 -: art. no. 167601

Oriented powder samples of NaxCoO2 are studied by Na-23 NMR and SQUID magnetometry. In nominal 0.50less than or equal toxless than or equal to0.70 solid state reacted samples the dominant phase synthesized has a single composition x(0)approximate to0.70. Three Na sites are identified from their single valued quadrupole effects and magnetic shifts, which implies a very definite order of the Na+ ions and of the Co charges in the CoO2 planes. The local susceptibility of the magnetic cobalt sites displays a large enhancement below 100 K with respect to the usually found high T Curie-Weiss law. This contrasts with the Pauli-like magnetism detected for xapproximate to0.35, the parent of the superconducting hydrated compound.