Magnetism and spin entropy in Ru doped Na0.5CoO2

Abstract

The effect of Ru doping on the magnetic coupling among Co ions and on the Seebeck effect in Na_0.5CoO₂ was systematically studied using density functional theory. It was found that the Ru dopant takes the 4+ oxidation state and replaces a Co⁴⁺ ion. In addition, the remaining Co⁴⁺ ions in Na_0.5CoO₂:Ru were stabilized in a low spin state. Magnetically, the Ru dopants couple in a ferrimagnetic manner with Co ions in the host lattice. Due to the higher electronic degeneracy of Ru⁴⁺ dopants, the Seebeck coefficient in Na_0.5CoO₂ is predicted to be higher than that of the pristine compound.