Electronic and magnetic structure of the mixed-valence cobaltite CaBaCo4O7

Abstract

Using first-principles density functional calculations we study the electronic and magnetic structure of mixed-valent cobaltite, CaBaCo${}_{4}$O${}_{7}$, consisting of alternate stacking of kagome and triangular layers. The compound belongs to the ``114'' series with the general formula, LnBa$M$${}_{4}$O${}_{7}$ ($M=$ Co, Fe). Our calculation shows that the strong orthorhombic distortion of the structure weakens the geometrical frustration and establishes the ferrimagnetic order, in good agreement with that reported by Caignaertet al. [Phys. Rev. B 81, 094417 (2010)]. Our calculated magnetic exchanges show strong Co-O-Co interactions both within the kagome layer and that connecting kagome with the triangular layer, thereby establishing the observed three-dimensional ordering. The reported magnetic ordering temperature is found to be smaller than that expected from the calculated magnetic exchanges, indicating the frustration being operative.