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

T. C. Kaspar, T. Droubay, V. Shutthanandan, S. M. Heald, C. M. Wang, D. E. McCready, S. Thevuthasan, J. D. Bryan, D. R. Gamelin, A. J. Kellock, M. F. Toney, X. Hong, C. H. Ahn, S. A. Chambers

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Abstract

The materials and magnetic properties of Cr-doped anatase TiO2 thin films deposited on LaAlO3 (001) and SrTiO3 (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 with energy dispersive x-ray spectroscopy, extended x-ray absorption fine structure, and Rutherford backscattering spectrometry in the channeling geometry. Epitaxial films deposited at ∼0.1 Å s were found to have a highly defected crystalline structure, as 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.

Original languageEnglish
Article number155327
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume73
Issue number15
DOIs
Publication statusPublished - 2006
Externally publishedYes

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Ferromagnetism
anatase
Titanium dioxide
ferromagnetism
Thin films
thin films
X rays
Diffraction
Oxygen
Crystalline materials
Magnetocrystalline anisotropy
x ray diffraction
Gene Conversion
Defects
Spin polarization
Epitaxial films
Hall effect
Rutherford backscattering spectroscopy
Magnetism
Oxygen vacancies

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

Kaspar, T. C., Droubay, T., Shutthanandan, V., Heald, S. M., Wang, C. M., McCready, D. E., ... Chambers, S. A. (2006). Ferromagnetism and structure of epitaxial Cr-doped anatase TiO2 thin films. Physical Review B - Condensed Matter and Materials Physics, 73(15), [155327]. https://doi.org/10.1103/PhysRevB.73.155327

Ferromagnetism and structure of epitaxial Cr-doped anatase TiO2 thin films. / Kaspar, T. C.; Droubay, T.; Shutthanandan, V.; Heald, S. M.; Wang, C. M.; McCready, D. E.; Thevuthasan, S.; Bryan, J. D.; Gamelin, D. R.; Kellock, A. J.; Toney, M. F.; Hong, X.; Ahn, C. H.; Chambers, S. A.

In: Physical Review B - Condensed Matter and Materials Physics, Vol. 73, No. 15, 155327, 2006.

Research output: Contribution to journalArticle

Kaspar, TC, Droubay, T, Shutthanandan, V, Heald, SM, Wang, CM, McCready, DE, Thevuthasan, S, Bryan, JD, Gamelin, DR, Kellock, AJ, Toney, MF, Hong, X, Ahn, CH & Chambers, SA 2006, 'Ferromagnetism and structure of epitaxial Cr-doped anatase TiO2 thin films', Physical Review B - Condensed Matter and Materials Physics, vol. 73, no. 15, 155327. https://doi.org/10.1103/PhysRevB.73.155327
Kaspar, T. C. ; Droubay, T. ; Shutthanandan, V. ; Heald, S. M. ; Wang, C. M. ; McCready, D. E. ; Thevuthasan, S. ; Bryan, J. D. ; Gamelin, D. R. ; Kellock, A. J. ; Toney, M. F. ; Hong, X. ; Ahn, C. H. ; Chambers, S. A. / Ferromagnetism and structure of epitaxial Cr-doped anatase TiO2 thin films. In: Physical Review B - Condensed Matter and Materials Physics. 2006 ; Vol. 73, No. 15.
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