title: Enhanced Magnetization of Cobalt Defect Clusters Embedded in TiO2-δFilms.
abstract: High magnetizations are desirable for spintronic devices that operate by manipulating electronic states using built-in magnetic fields. However, the magnetic moment in promising dilute magnetic oxide nanocomposites is very low, typically corresponding to only fractions of a Bohr magneton for each dopant atom. In this study, we report a large magnetization formed by ion implantation of Co into amorphous TiO2-δfilms, producing an inhomogeneous magnetic moment, with certain regions producing over 2.5 μBper Co, depending on the local dopant concentration. Polarized neutron reflectometry was used to depth-profile the magnetization in the Co:TiO2-δnanocomposites, thus confirming the pivotal role of the cobalt dopant profile inside the titania layer. X-ray photoemission spectra demonstrate the dominant electronic state of the implanted species is Co0, with a minor fraction of Co2+. The detected magnetizations have seldom been reported before and lie near the upper limit set by Hund's rules for Co0, which is unusual because the transition metal's magnetic moment is usually reduced in a symmetric 3D crystal-field environment. Low-energy positron annihilation lifetime spectroscopy indicates that defect structures within the titania layer are strongly modified by the implanted Co. We propose that a clustering motif is promoted by the affinity of the positively charged implanted species to occupy microvoids native to the amorphous host. This provides a seed for subsequent doping and nucleation of nanoclusters within an unusual local environment.
authors.affiliation: Research School of Chemistry, Australian National University , Canberra, Australian Capital Territory 2601, Australia.|The Institute for Superconducting and Electronic Materials, University of Wollongong , Wollongong, New South Wales 2522, Australia.|Australian Nuclear Science and Technology Organization , Lucas Heights, New South Wales 2234, Australia.
authors.forename: David L
authors.identifier: http://orcid.org/0000-0003-2383-1619
authors.initials: DL
authors.lastname: Cortie
authors.affiliation: Max Planck Institute für Festkörperforschung , Stuttgart 70569, Germany.|Max Planck Society , Outstation at the MLZ, Garching 85748, Germany.
authors.forename: Yury
authors.initials: Y
authors.lastname: Khaydukov
authors.affiliation: Max Planck Institute für Festkörperforschung , Stuttgart 70569, Germany.|Max Planck Society , Outstation at the MLZ, Garching 85748, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Keller
authors.affiliation: Brookhaven National Laboratory , Upton, New York 11973, United States.|ARC Centre for Antimatter-Matter Studies, Australian National University , Canberra Australian Capital Territory 0200, Australia.
authors.forename: David J
authors.initials: DJ
authors.lastname: Sprouster
authors.affiliation: ARC Centre for Antimatter-Matter Studies, Australian National University , Canberra Australian Capital Territory 0200, Australia.
authors.forename: Jacob S
authors.initials: JS
authors.lastname: Hughes
authors.affiliation: ARC Centre for Antimatter-Matter Studies, Australian National University , Canberra Australian Capital Territory 0200, Australia.
authors.forename: James P
authors.identifier: http://orcid.org/0000-0003-4489-4926
authors.initials: JP
authors.lastname: Sullivan
authors.affiliation: The Institute for Superconducting and Electronic Materials, University of Wollongong , Wollongong, New South Wales 2522, Australia.
authors.forename: Xiaolin L
authors.initials: XL
authors.lastname: Wang
authors.affiliation: Australian Nuclear Science and Technology Organization , Lucas Heights, New South Wales 2234, Australia.
authors.forename: Anton P
authors.initials: AP
authors.lastname: Le Brun
authors.affiliation: Australian Nuclear Science and Technology Organization , Lucas Heights, New South Wales 2234, Australia.|School of Physics, University of New South Wales , Sydney, New South Wales 2052, Australia.
authors.forename: Joel
authors.initials: J
authors.lastname: Bertinshaw
authors.affiliation: Australian Nuclear Science and Technology Organization , Lucas Heights, New South Wales 2234, Australia.|School of Physics, University of New South Wales , Sydney, New South Wales 2052, Australia.|Department of Physics, California State University , San Bernardino, California 92407, United States.
authors.forename: Sara J
authors.initials: SJ
authors.lastname: Callori
authors.affiliation: Australian Nuclear Science and Technology Organization , Lucas Heights, New South Wales 2234, Australia.
authors.forename: Robert
authors.initials: R
authors.lastname: Aughterson
authors.affiliation: Australian Nuclear Science and Technology Organization , Lucas Heights, New South Wales 2234, Australia.
authors.forename: Michael
authors.initials: M
authors.lastname: James
authors.affiliation: Australian Nuclear Science and Technology Organization , Lucas Heights, New South Wales 2234, Australia.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Evans
authors.affiliation: Australian Nuclear Science and Technology Organization , Lucas Heights, New South Wales 2234, Australia.
authors.forename: Gerry
authors.initials: G
authors.lastname: Triani
authors.affiliation: Australian Nuclear Science and Technology Organization , Lucas Heights, New South Wales 2234, Australia.|Department of Physics and Materials Science, City University of Hong Kong , Kowloon, Hong Kong Special Administrative Region, China.
authors.forename: Frank
authors.initials: F
authors.lastname: Klose
keywords: dilute magnetic oxide semiconductor; nanoclusters; nanocomposite; nanomagnetism; spintronics