AVS 52nd International Symposium
    Magnetic Interfaces and Nanostructures Thursday Sessions
       Session MI-ThA

Paper MI-ThA6
Structural, Electronic and Magnetic Properties of MBE Grown Ti-doped @alpha@-Fe@sub 2@O@sub 3@

Thursday, November 3, 2005, 3:40 pm, Room 204

Session: Magnetic Oxides
Presenter: S.A. Chambers, Pacific Northwest National Laboratory
Authors: S.A. Chambers, Pacific Northwest National Laboratory
T.C. Droubay, Pacific Northwest National Laboratory
S.M. Heald, Pacific Northwest National Laboratory
C.M. Wang, Pacific Northwest National Laboratory
K. Rosso, Pacific Northwest National Laboratory
Correspondent: Click to Email
@alpha@-Fe@sub 2@O@sub 3@ is an antiferromagnetic wide bandgap semiconductor (E@sub g@ = 2.2 eV) which exhibits strong ferromagnetic coupling within cation layers perpendicular to the c axis, and antiferromagnetic coupling between adjacent cation layers. LSDA + U calculations predict that substituting Ti for Fe should lead to a ferrimagnetic state with a large moment per Ti because Ti is predicted to substitute for Fe preferentially in alternating cation layers perpendicular to the c axis.@footnote 1,2@ To test this prediction, we have used oxygen plasma assisted molecular beam epitaxy to grow @alpha@-Ti@sub x@Fe@sub 2-x@O@sub 3@, for which x varied between 0.01 and 0.04, on @alpha@-Al@sub 2@O@sub 3@(0001). Excellent heteroepitaxy was achieved by first growing a @alpha@-Cr@sub 2@O@sub 3@ buffer layer to grade the lattice mismatch between @alpha@Fe@sub 2@O@sub 3@ and @alpha@-Al@sub 2@O@sub 3@. All Fe was found to be in the +3 charge state by Fe K-shell XAS and Fe 2p XPS. Ti was found to be in the +4 charge state and to uniformly substitute for Fe(III) in the lattice by Ti K-shell XAS and EXAFS, along with ion channeling. The conductivity increased monotonically with x, achieving a value of ~100 Ohm-cm at x = 0.04. All doped films were found to be weakly ferromagnetic at room temperature, as expected if Fe ions were replaced with Ti(IV) ions in a statistical fashion in all cation layers. The coercive field was found to be ~800 Oe, independent of x. The moment was found to be ~0.5 µ@sub B@ per Ti dopant, considerably lower than the 4 µ@sub B@ per Ti dopant predicted by LSDA + U theory.@footnote 1,2@. @FootnoteText@ @footnote 1@ W.H. Butler et al., J. Appl. Phys. 93, 7882 (2003).@footnote 2@ A. Bandyopadhyay et al., Phys. Rev. B 69, 174429 (2004).