NMR study of the magnetic and metal-insulator transitions in Na0.5CoO2: a nesting scenario

الأصل · EN

Co and Na NMR are used to probe the local susceptibility and charge state of the two Co sites of the Na-ordered orthorhombic Na0.5CoO2. Above Tₙ=86K, both sites display a similar T-dependence of the spin shift, suggesting that there is no charge segregation into Co3+ and Co4+ sites. Below Tₙ, the magnetic long range commensurate order found is only slightly affected by the metal-insulator transition (MIT) at TₘIT=51K. Furthermore, the electric field gradient at the Co site does not change at these transitions, indicating the absence of charge ordering. All these observations can be explained by successive SDW induced by two nestings of the Fermi Surface specific to the x=0.5 Na-ordering.