title: Origin of magnetism and quasiparticles properties in Cr-doped TiO2.
abstract: Combining the local spin density approximation (LSDA)+U and an analysis of superexchange interactions beyond density functional theory, we describe the magnetic ground state of Cr-doped TiO2, an intensively studied and debated dilute magnetic oxide. In parallel, we correct our LSDA+U (+ superexchange) ground state through GW corrections (GW@LSDA+U) that reproduce the position of the impurity states and the band gaps in satisfying agreement with experiments. Because of the different topological coordinations of Cr-Cr bonds in the ground states of rutile and anatase, superexchange interactions induce either ferromagnetic or antiferromagnetic couplings of Cr ions. In Cr-doped anatase, this interaction leads to a new mechanism which stabilizes a (nonrobust) ferromagnetic ground state, in keeping with experimental evidence, without the need to invoke F-center exchange. The interplay between structural defects and vacancies in contributing to the superexchange is also unveiled.
authors.affiliation: EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
authors.forename: F
authors.initials: F
authors.lastname: Da Pieve
authors.forename: S
authors.initials: S
authors.lastname: Di Matteo
authors.forename: T
authors.initials: T
authors.lastname: Rangel
authors.forename: M
authors.initials: M
authors.lastname: Giantomassi
authors.forename: D
authors.initials: D
authors.lastname: Lamoen
authors.forename: G-M
authors.initials: GM
authors.lastname: Rignanese
authors.forename: X
authors.initials: X
authors.lastname: Gonze