23Na NMR study of non-superconducting double-layer hydrate NaxCoO2 · yH2O

✍ Scribed by H. Ohta; Y. Itoh; C. Michioka; K. Yoshimura

• Publisher: Elsevier Science
• Year: 2006
• Tongue: English
• Weight: 156 KB
• Volume: 445-448
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/j.physc.2006.03.080

✦ Synopsis

We report 23 Na NMR studies of the polycrystalline samples of double-layer hydrated cobalt oxides Na x CoO 2 AE yH 2 O (x $ 0.35 and y $ 1.3) with the superconducting transition temperatures T c < 1.8 K and $4.5 K, and the dehydrated Na x CoO 2 (x $ 0.35). The hyperfine field and the electric field gradient at the Na sites in the non-hydrated Na 0.7 CoO 2 and the dehydrated Na 0.35 CoO 2 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/ 23 T 1 of the non-superconducting double-layer hydrate Na x CoO 2 AE yH 2 O is found to be similar to that of the non-hydrated Na 0.7 CoO 2 , whose spin dynamics is understood by A-type (intralayer ferromagnetic and inter-layer antiferromagnetic) spin fluctuations. The superconducting phase is located close to the quantum critical point with the A-type magnetic instability.