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59Co NMR study of the Co states in superconducting and anhydrous cobaltates

I. R. Mukhamedshin·H. Alloul·G. Collin·N. Blanchard
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Abstract

$^{59}$Co NMR spectra in oriented powders of Na$_{0.35}$CoO$_{2}$ and in its hydrated superconducting phase (HSC) Na$_{0.35}$CoO$_{2}$,1.3H$_{2}$O reveal a single electronic Co state with identical $T$ independent NMR shift tensor. These phases differ markedly from Na$_{0.7}$CoO$_{2}$, in which we resolve 3 types of Co sites. The large T variation of their spin susceptibilities $χ^{s}$ and the anisotropy of the orbital susceptibility $χ^{orb}$ allow us to conclude that charge disproportionation occurs, in a non magnetic Co$^{3+}$ and two magnetic sites with about 0.3 and 0.7 holes in the $t_{2g}$ multiplet. The data are consistent with those for the single Co site in the anhydrous and HSC phase assuming the expected Co$^{3.65+}$ charge.

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I. R. Mukhamedshin, H. Alloul, G. Collin, N. Blanchard. 2005-05-16. 59Co NMR study of the Co states in superconducting and anhydrous cobaltates. https://doi.org/10.1103/physrevlett.94.247602

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