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Title: Ferromagnetism and structure of epitaxial Cr-doped anatase TiO2 thin films

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER)
OSTI Identifier:
1152577
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review B; Journal Volume: 73; Journal Issue: 15
Country of Publication:
United States
Language:
English

Citation Formats

T.,Kaspar, T.,Droubay, V.,Shutthanandan, S.,Heald, C.,Wang, D.,McCready, S.,Thevuthasan, J.,Bryan, D.,Gamelin, A.,Kellock, M.,Toney, X.,Hong, C.,Ahn, and S.,Chambers. Ferromagnetism and structure of epitaxial Cr-doped anatase TiO2 thin films. United States: N. p., 2006. Web. doi:10.1103/PhysRevB.73.155327.
T.,Kaspar, T.,Droubay, V.,Shutthanandan, S.,Heald, C.,Wang, D.,McCready, S.,Thevuthasan, J.,Bryan, D.,Gamelin, A.,Kellock, M.,Toney, X.,Hong, C.,Ahn, & S.,Chambers. Ferromagnetism and structure of epitaxial Cr-doped anatase TiO2 thin films. United States. doi:10.1103/PhysRevB.73.155327.
T.,Kaspar, T.,Droubay, V.,Shutthanandan, S.,Heald, C.,Wang, D.,McCready, S.,Thevuthasan, J.,Bryan, D.,Gamelin, A.,Kellock, M.,Toney, X.,Hong, C.,Ahn, and S.,Chambers. Sat . "Ferromagnetism and structure of epitaxial Cr-doped anatase TiO2 thin films". United States. doi:10.1103/PhysRevB.73.155327.
@article{osti_1152577,
title = {Ferromagnetism and structure of epitaxial Cr-doped anatase TiO2 thin films},
author = {T.,Kaspar and T.,Droubay and V.,Shutthanandan and S.,Heald and C.,Wang and D.,McCready and S.,Thevuthasan and J.,Bryan and D.,Gamelin and A.,Kellock and M.,Toney and X.,Hong and C.,Ahn and S.,Chambers},
abstractNote = {},
doi = {10.1103/PhysRevB.73.155327},
journal = {Physical Review B},
number = 15,
volume = 73,
place = {United States},
year = {Sat Apr 01 00:00:00 EST 2006},
month = {Sat Apr 01 00:00:00 EST 2006}
}
  • The materials and magnetic properties of Cr-doped anatase TiO 2 thin films deposited on LaAlO 3(001) and SrTiO 3(001) substrates by oxygen-plasma-assisted molecular beam epitaxy have been studied in detail to elucidate the origin of ferromagnetic ordering. Cr substitution for Ti in the anatase lattice, with no evidence of Cr interstitials, segregation, or secondary phases, was independently confirmed by transmission electron microscopy (TEM) with energy dispersive x-ray (EDX) spectroscopy, extended x-ray absorption fine structure (EXAFS), and Rutherford backscattering spectrometry (RBS) in the channeling geometry. Epitaxial films deposited at ~0.1 Å/s were found to have a highly defected crystalline structure, asmore » quantified by high resolution x-ray diffraction (XRD). These films were also ferromagnetic at room temperature with a moment of ~0.5 μB/Cr, Curie temperatures in the range of 400 – 700°C, and exhibited shape and in-plane magnetocrystalline anisotropy. However, no free carrier spin polarization was observed by Hall effect measurements, raising questions about the mechanism of magnetism. Films deposited slowly (~0.015 Å/s) possessed a nearly perfect crystalline structure as characterized by XRD. Contrary to expectations, these films exhibited negligible ferromagnetism at all Cr concentrations. Annealing in vacuum to generate additional oxygen defects and free carrier electrons did not significantly increase the ferromagnetic ordering in either fast- or slow-grown films. These results contradict both oxygen-vacancy-derived free-carrier-mediated exchange and F-center-mediated bound magnetic polaron exchange mechanisms, and instead indicate the primary role of extended structural defects in mediating the ferromagnetic ordering in doped anatase films.« less
  • No abstract prepared.
  • The room temperature ferromagnetism recently discovered in transition metal doped oxides makes of them unique materials for new spintronic technologies. However, the mechanism responsible for this behavior has remained elusive. Here we use Z-contrast scanning transmission electron microscopy to image the Co and find that the magnetic phase in Co doped TiO2 films consists of a superstructure of interstitial Co atoms homogeneously distributed in the anatase lattice. Detailed analysis of the energy-loss near edge structure at the Ti L2,3 edge shows that the activation of ferromagnetism by post growth vacuum annealing involves the creation of Co - Ti3+- oxygen vacancymore » defect complexes. First-principles, spin-polarized density functional theory calculations confirm that these defect complexes have the lowest energy configuration and that their magnetic moment is in agreement with experimental observations.« less
  • We have investigated the properties of N-doped TiO2 anatase grown by plasma-assisted molecular beam epitaxy on LaAlO3(001) substrates. Phase-pure epitaxial films in which N substitutes for O with no secondary phases formation occur only over a narrow range of fluxes. The N solubility is limited to ~0.2 at. % of the anions and is an order of magnitude lower than that found in N-doped rutile. N substitution for O results in N 2p derived states off the top of the anatase valence band and the associated red shift in the optical bandgap.
  • Cited by 16