Na ordering imprints a metallic kagomé lattice onto the Co planes of Na2/3CoO2H. Alloul1, I. R. Mukhamedshin1, 2, T. A. Platova1, 2 and A. V. Dooglav2
1 Laboratoie de Physique des Solides, UMR CNRS 8502, Université Paris-Sud - 91405 Orsay, France, EU
2 Physics Department, Kazan State University - 420008 Kazan, Russia
received 21 December 2008; accepted in final form 4 February 2009; published February 2009
published online 4 March 2009
We report 23Na and 59Co nuclear magnetic (NMR) and quadrupolar resonance (NQR) studies for the x = 2/3 phase of the lamellar oxide NaxCoO2, which allowed us to establish reliably the atomic order of the Na layers and their stacking between the CoO2 slabs. We evidence that the Na+ order stabilizes filled non-magnetic Co3+ 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.
71.27.+a - Strongly correlated electron systems; heavy fermions.
71.28.+d - Narrow-band systems; intermediate-valence solids.
76.60.-k - Nuclear magnetic resonance and relaxation.
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