AVS 66th International Symposium & Exhibition
    Complex Oxides: Fundamental Properties and Applications Focus Topic Wednesday Sessions
       Session OX+EM+MI+SS-WeM

Paper OX+EM+MI+SS-WeM13
Incorporation of Ti into Epitaxial Films of Magnetite

Wednesday, October 23, 2019, 12:00 pm, Room A220-221

Session: Electronic and Magnetic Properties of Complex Oxide Surfaces and Interfaces
Presenter: Tiffany Kaspar, Pacific Northwest National Laboratory
Authors: T.C. Kaspar, Pacific Northwest National Laboratory
S.R. Spurgeon, Pacific Northwest National Laboratory
D.K. Schreiber, Pacific Northwest National Laboratory
S.D. Taylor, Pacific Northwest National Laboratory
M.E. Bowden, Pacific Northwest National Laboratory
S.A. Chambers, Pacific Northwest National Laboratory
Correspondent: Click to Email
Magnetite, Fe3O4, exhibits metallic conductivity via electron hopping between Fe2+ and Fe3+ occupying octahedral sites in the spinel lattice. As Ti4+ is doped into the octahedral sites of magnetite (the titanomagnetite series), an equal fraction of Fe3+ is reduced to Fe2+ to maintain charge neutrality. The site occupancies of Fe2+ and Fe3+ determine the transport properties of the titanomagnetite series; the end-member ulvöspinel, Fe2TiO4, exhibits p-type semiconducting transport properties. The Fe2+/Fe3+ site occupancy remains controversial, but is likely in part a function of the lattice strain induced by doping smaller Ti4+ into the lattice. Here, we have deposited titanomagnetites and ulvöspinel as well-defined epitaxial thin films on MgO, MgAl2O4, and Al2O3 substrates by oxygen-plasma-assisted molecular beam epitaxy. The incorporation of Ti into the magnetite lattice is found to depend strongly on deposition conditions and substrate orientation. We have characterized the crystalline structure, phase segregation, and surface morphology with XRD, STEM/EDS, APT, and AFM, and related these to the kinetic and thermodynamic factors determined by the deposition conditions. The Fe valence state is evaluated with in situ XPS. The impact of film structure and Fe oxidation state on the electrical transport properties of the films will be discussed.