Physics – Condensed Matter – Superconductivity
Scientific paper
2006-05-19
Physica C : Superconductivity, Volumes 445-448, 1 October 2006, Pages 69-72
Physics
Condensed Matter
Superconductivity
4 pages, 4 figures
Scientific paper
10.1016/j.physc.2006.03.080
We report 23Na NMR studies of the polycrystalline samples of double-layer hydrated cobalt oxides NaxCoO2.yH2O (x ~ 0.35 and y ~ 1.3) with the superconducting transition temperatures Tc < 1.8K and ~4.5K, and the dehydrated NaxCoO2 (x ~ 0.35). The hyperfine field and the electric field gradient at the Na sites in the non-hydrated Na0.7CoO2 and the dehydrated Na0.35CoO2 are found to be significantly reduced by the hydration, which indicates a strong shielding effect of the intercalated water molecules on the Na sites. The temperature dependence of 23 Na nuclear spin-lattice relaxation rate 1/23T1 of the non-superconducting double-layer hydrate NaxCoO2.yH2O is found to be similar to that of the non-hydrated Na0.7CoO2, whose spin dynamics is understood by A-type (intra-layer ferromagnetic and inter-layer antiferromagnetic) spin fluctuations. The superconducting phase is located close to the quantum critical point with the A-type magnetic instability.
Itoh Yusuke
Michioka Chishiro
Ohta Hideki
Yoshimura Kazuyoshi
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