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23Na NMR Evidence for Charge Order and Anomalous Magnetism in NaxCoO2

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

We have compared by $^{23}$Na NMR and magnetic susceptibility the magnetic properties of oriented powder samples of Na$_{x}$CoO$_{2}$ compounds. The NMR spectra are found identical for various samples with nominal $0.50\leq x\leq 0.70,$ which establishes that the dominant phase has a single composition $x\approx 0.70$. Three Na sites are identified from their single valued quadrupole effects and magnetic shifts which implies a very definite order of the Na$^{+}$ ions and of the Co charges in the CoO$_{2}$ planes. The local susceptibility of the magnetic cobalt sites displays a large enhancement below 100 K with respect to the usually found high $T$ Curie-Weiss law. A very distinct much weaker Pauli like magnetism is detected for $x\approx 0.35$, the parent of the superconducting hydrated compound.

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I. R. Mukhamedchine, H. Alloul, G. Collin, N. Blanchard. 2004-02-03. 23Na NMR Evidence for Charge Order and Anomalous Magnetism in NaxCoO2. https://arxiv.org/abs/cond-mat/0402074

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