AVS 51st International Symposium
    Magnetic Interfaces and Nanostructures Thursday Sessions
       Session MI-ThM

Paper MI-ThM7
Room-Temperature Ferromagnetism in Cr-doped TiO@sub 2@ Anatase

Thursday, November 18, 2004, 10:20 am, Room 304A

Session: Magnetic Oxides and Half-Metallics
Presenter: S.A. Chambers, Pacific Northwest National Laboratory
Authors: T.C. Droubay, Pacific Northwest National Laboratory
S.M. Heald, Pacific Northwest National Laboratory
S.V. Shutthanandan, Pacific Northwest National Laboratory
S.T. Thevuthasan, Pacific Northwest National Laboratory
S.A. Chambers, Pacific Northwest National Laboratory
J. Osterwalder, Physik-Institut der Universitat Zurich, Switzerland
Correspondent: Click to Email
Since the initial discovery in 2001, the possibility of ferromagnetism in doped oxide semiconductors has spawned a flurry of research activity around the world. Among the new materials that have been investigated, Co-doped TiO@sub 2@ anatase has garnered much attention due to its ferromagnetic response, which persists well above room temperature. Reports of doping TiO@sub 2@ anatase with other magnetic transition elements, however, are scarce. We have carried out a detailed study of the growth and properties of epitaxial Cr-doped TiO@sub 2@ anatase on LaAlO@sub 3@ (001) using oxygen-plasma assisted molecular beam epitaxy. These films are found to be single-phase and homogenous, with Cr uniformly substituting for Ti in the lattice. Cr K-shell x-ray absorption near-edge spectroscopy shows that the formal oxidation state of Cr is +3 throughout the films, with no evidence for either elemental Cr or half-metallic CrO@sub 2@. These films are insulating as grown, yet exhibit room temperature ferromagnetism aligned in-plane with a saturation magnetization of ~0.6 Bohr magnetons per Cr atom. Introduction of free electrons by incorporation of additional oxygen vacancies via post-growth annealing in UHV increases both the n-type conductivity and the saturation magnetization, without deleterious effects on the homogeneity or crystallinity of the films. None of the existing models of magnetism in semiconductors can explain ferromagnetism in the absence of free carriers for a dilute system. We will present a novel exchange mechanism to do so.