  We synthesized Nax(H3O)zCoO2yH2O samples with various Na/H3O ratios but with
the constant Co valence of s = +3.40, and measured their magnetic properties to
draw phase diagrams of the system. The superconductivity is very sensitive to
the Na/H3O ratio. With varying x under fixed s of +3.40, magnetically ordered
phase appears in the intermediate range of x sandwiched by two separated
superconducting phases, suggesting that the superconductivity is induced by
moderately strong magnetic interactions. In the vicinity of the magnetic phase,
transition from the superconducting state to the magnetically ordered state was
induced by applying high magnetic field. This transition is of the second
order, at least, above 1.8 K. The upper-critical field is expected to be much
higher than the Pauli limit for a phase located far away from the magnetic
phase regarding the Na/H3O ratio.
