  Macroscopic magnetization, muon spin rotation (muSR), and NMR measurements
were carried out to study magnetism in the Na1CoO2 cobaltate. Using SQUID
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, muSR 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 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 NMR, whose determination of cobalt shift and
quadrupolar parameters allows us to give a reference value of the Co3+ orbital
shift in cobaltates.
