title: Role of Ti 3d carriers in mediating the ferromagnetism of Co∶TiO2 anatase thin films.
abstract: We study the surface and bulk electronic structure of the room-temperature ferromagnet Co∶TiO(2) anatase films using soft- and hard-x-ray photoemission spectroscopy with probe sensitivities of ∼1 and ∼10  nm, respectively. We obtain direct evidence of metallic Ti(3+) states in the bulk, which get suppressed to give a surface semiconductor, thus indicating the difference in electronic structure between surface and bulk. X-ray absorption and resonant photoemission spectroscopy reveal Ti(3+) electrons at the Fermi level (E(F)) and high-spin Co(2+) electrons occurring away from E(F). The results show the importance of the charge neutrality condition: Co(2+)+V(O)(2-)+2Ti(4+)↔Co(2+)+2Ti(3+) (V(O) is oxygen vacancy), which gives rise to the elusive Ti 3d carriers mediating ferromagnetism via the Co 3d-O 2p-Ti 3d exchange interaction pathway of the occupied orbitals.
authors.affiliation: RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Ohtsuki
authors.forename: A
authors.initials: A
authors.lastname: Chainani
authors.forename: R
authors.initials: R
authors.lastname: Eguchi
authors.forename: M
authors.initials: M
authors.lastname: Matsunami
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authors.initials: Y
authors.lastname: Takata
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authors.initials: M
authors.lastname: Taguchi
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authors.initials: Y
authors.lastname: Nishino
authors.forename: K
authors.initials: K
authors.lastname: Tamasaku
authors.forename: M
authors.initials: M
authors.lastname: Yabashi
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authors.initials: T
authors.lastname: Ishikawa
authors.forename: M
authors.initials: M
authors.lastname: Oura
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authors.initials: Y
authors.lastname: Senba
authors.forename: H
authors.initials: H
authors.lastname: Ohashi
authors.forename: S
authors.initials: S
authors.lastname: Shin