Evidence of a single nonmagnetic Co3+ state in the Na1CoO2 cobaltate -: art. no. 094404

Macroscopic magnetization, muon spin rotation (mu SR), and NMR measurements were carried out to study magnetism in the Na1CoO2 cobaltate. Using superconducting quantum interference device measurements, Na1CoO2 is shown to have a bulk magnetic susceptibility much lower and flatter than that of NaxCoO2 with x=0.7-0.9. In fact, mu SR yields a signal of mostly nonmagnetic origin, which is attributed to the x=1 phase. The intrinsic cobalt spin susceptibility corresponding to this x=1 phase is measured using Na-23 NMR. It is indeed found to be almost zero, in agreement with a low-spin 3+ charge state of all cobalt atoms. This single state of Co ions in CoO2 planes is confirmed by Co-59 NMR, whose determination of cobalt shift and quadrupolar parameters allows us to give a reference value of the Co3+ orbital shift in cobaltates.