Na ordering imprints a metallic kagome lattice onto the Co planes of Na2/3CoO2

Abstract

We report ${}^{23}$Na and ${}^{59}$Co nuclear magnetic (NMR) and quadrupolar resonance (NQR) studies for the $x=2/3$ phase of the lamellar oxide Na${}_x$CoO${}_2$, which allowed us to establish reliably the atomic order of the Na layers and their stacking between the CoO${}_2$ slabs. We evidence that the Na${}^{+}$ order stabilizes filled non magnetic Co${}^{3+}$ ions on 25% of the cobalt sites arranged in a triangular sublattice. The transferred holes are delocalized on the 75% complementary cobalt sites which unexpectedly display a planar cobalt kagomé structure. These experimental results resolve a puzzling issue by precluding localized moments pictures for the magnetic properties. They establish that the quasi ferromagnetic properties result from a narrow band connecting a frustrated arrangement of atomic orbitals, and open the route to unravel through similar studies the electronic properties of the diverse ordered phases of sodium cobaltates.

6 pages, 5 figures. Accepted at EPL (Europhysics Letters)

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Cited by in corpus (7)

• Magnetic fluctuations and specific heat in NaxCoO2 near a Lifshitz topological transition
• Na order and Co charge disproportionation in Na${}_x$CoO${}_2$
• Evolution of Co charge disproportionation with Na order in Na${}_x$CoO${}_2$
• Origin of the electron disproportionation in the metallic sodium cobaltates
• From Friedel oscillations and Kondo effect to the pseudogap in cuprates
• Enhancement of the effective disorder potential and the thermopower in Na${}_x$CoO${}_2$ through the electron-phonon coupling
• Complex magnetic differentiation of cobalts in Na${}_x$CoO${}_2$ with 22K Néel temperature