title: Nature of magnetism in Ca3Co2O6.
abstract: We find using local spin density approximation + Hubbard U band structure calculations that the novel one-dimensional cobaltate Ca3Co2O6 is not a ferromagnetic half-metal but a Mott insulator. Both the octahedral and the trigonal Co ions are formally trivalent, with the octahedral being in the low-spin and the trigonal in the high-spin state. The inclusion of the spin-orbit coupling leads to the occupation of the minority-spin d2 orbital for the unusually coordinated trigonal Co, producing a giant orbital moment (1.57 microB). It also results in an anomalously large magnetocrystalline anisotropy (of order 70 meV), elucidating why the magnetism is highly Ising-like. The role of the oxygen holes, carrying an induced magnetic moment of 0.13 microB per oxygen, for the exchange interactions is discussed.
authors.affiliation: II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Köln, Germany.
authors.forename: Hua
authors.initials: H
authors.lastname: Wu
authors.forename: M W
authors.initials: MW
authors.lastname: Haverkort
authors.forename: Z
authors.initials: Z
authors.lastname: Hu
authors.forename: D I
authors.initials: DI
authors.lastname: Khomskii
authors.forename: L H
authors.initials: LH
authors.lastname: Tjeng