23Na NMR Studies of Non-superconducting and Superconducting Na0.35CoO2-1.3H2O (Tc < 1.8 and ~ 4.5 K)

TL;DR

This study uses 23Na NMR to compare the magnetic properties of non-hydrated and hydrated Na-Co-O compounds, revealing how hydration affects spin dynamics and superconductivity in these materials.

Contribution

It provides new insights into the spin fluctuations and magnetic instabilities associated with superconductivity in bilayer hydrated cobalt oxides.

Findings

23Na NMR relaxation rates decrease with hydration.

Superconducting samples are near A-type magnetic instability.

Spin dynamics in non-superconducting hydrate resemble non-hydrated compound.

Abstract

We report 23Na NMR studies of the polycrystalline samples of bilayer hydrated cobalt oxides Na0.35CoO2-1.3H2O with the superconducting transition temperatures Tc < 1.8 and ~ 4.5 K. The magnitude of the 23Na nuclear spin-lattice relaxation rate 23(1/T1) significantly decreased from non-hydrated Na0.7CoO2 to the bilayer hydrates. We found that the temperature dependence of 23(1/T1) of the non-superconducting bilayer hydrate is similar to that of the non-hydrated Na0.7CoO2, the spin dynamics of which is understood by A-type (intra-layer ferromagnetic and inter-layer antiferromagnetic) spin fluctuations. The superconducting phase is located close to the A-type magnetic instability.