Abstract
Nuclear quadrupole frequency (νQ) and spin-lattice relaxation rate 1/T1 of Co were measured on various bilayered hydrate (BLH) NaxCoO2·yH2O (y∼1.3) with different values of superconducting (SC) and magnetic-transition temperatures, Tc and TM, together with non-SC monolayered hydrate (MLH) NaxCoO2·yH2O (y∼0.7). In the temperature range above 70K, 1/T1T in all samples follows the similar temperature dependence as each other. In the BLH compounds, 1/T1T is enhanced with decreasing temperature below 70K, and the values of 1/T1T at Tc are larger in the higher-ν3 sample, where ν3 is the peak frequency of the NQR spectrum arising from ±5/2↔±7/2 transitions. The magnetic ordering is indicated from the prominent divergence of 1/T1T at TM and the presence of the internal field at the Co nuclear site in the samples with ν3 higher than 12.5MHz. We analyze the temperature dependence of 1/T1T in all samples on the basis of identical formula, and discuss the relationship between magnetic fluctuations and superconductivity in the BLH cobaltate.
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