AVS 50th International Symposium
    Electronic Materials and Devices Wednesday Sessions
       Session EM-WeM

Paper EM-WeM3
MBE Growth and Properties of Fe-, Cr- and Mn-doped TiO2 Rutile and Anatase

Wednesday, November 5, 2003, 9:00 am, Room 321/322

Session: Multifunctional Electronic Materials
Presenter: S.A. Chambers, Pacific Northwest National Laboratory
Authors: S.A. Chambers, Pacific Northwest National Laboratory
S. Thevuthasan, Pacific Northwest National Laboratory
T. Droubay, Pacific Northwest National Laboratory
S.M. Heald, Pacific Northwest National Laboratory
C.M. Wang, Pacific Northwest National Laboratory
A.S. Lea, Pacific Northwest National Laboratory
V. Shutthanandan, Pacific Northwest National Laboratory
J. Osterwalder, University of Zurich, Switzerland
Y.J. Kim, Hanbat National University, Korea
R.P. Sears, University of Connecticut
B. Taylor, University of Connecticut
B.S. Sinkovic, University of Connecticut
Correspondent: Click to Email
Room temperature ferromagnetism in Co-doped anatase TiO@sub 2@ has inspired a number of experimental and theoretical efforts. A high Curie point, good electron mobility, and optical transparency are attractive for use in spin electronics and optoelectronics. A natural question concerns the use of other magnetic dopants. Combinatorial doping of anatase and rutile with Sc, V, Cr, Mn, Fe, Ni, Cu using laser ablation by Matsumoto et al. reveal that only Co-doped anatase is ferromagnetic. However, DFT calculations by van Schilfgaarde for Cr, Mn, Fe and Co in anatase predict that Co, Cr and Fe make the material ferromagnetic, whereas Mn is antiferromagnetic. We are currently exploring Fe and Cr as dopants in MBE-grown TiO@sub 2@ rutile and anatase, and plan to investigate Mn in the near future. The substrates for rutile and anatase films are rutile TiO@sub 2@(110) and LaAlO@sub 3@(001), respectively. Films were characterized with RHEED, XPS, XPD, XAS, EXAFS, XMCD, AFM, SAM, TEM and MOKE. Cr and Mn are more likely to substitute for Ti in rutile than Fe because CrO@sub 2@ and MnO@sub 2@ exhibit rutile structures that are reasonably well lattice matched to TiO@sub 2@. No such phase exists for Fe. Moreover, CrO@sub 2@ is a half-metallic ferromagnet in the bulk. Cr indeed substitutes for Ti in the rutile lattice, and assumes a +3 formal oxidation state for doping levels of a few atomic percent. The first films have been found to be antiferromagnetic. In contrast, attempting to dope rutile with Fe leads to secondary phase Fe@sub 3@O@sub 4@. Fe (II) and Fe(III) are present, as expected if Fe@sub 3@O@sub 4@ is present. In addition, these films exhibit magnetic hysteresis and circular dichroism, but these signals are presumably due to the presence of minority phase Fe@sub 3@O@sub 4@. Cr exhibits a +3 oxidation state and substitutes for Ti for doping levels of a few atomic percent in anatase. Magnetic measurements of these films are pending at the time of writing of the abstract.