AVS 61st International Symposium & Exhibition
    Magnetic Interfaces and Nanostructures Monday Sessions
       Session MI-MoA

Paper MI-MoA11
Control of Graphene Nucleation on Magnetic Oxides: Spintronics without Spin Injection

Monday, November 10, 2014, 5:20 pm, Room 311

Session: Topological Insulators/Rashba Effect
Presenter: Yuan Cao, University of North Texas
Authors: Y. Cao, University of North Texas
P. Kumar, Indian Institute of Technology-Mandi, India
I. Tanabe, University of Nebraska-Lincoln
J. Beatty, University of North Texas
M. Driver, University of North Texas
A. Kashyap, Indian Institute of Technology-Mandi, India
P.A. Dowben, University of Nebraska-Lincoln
J.A. Kelber, University of North Texas
Correspondent: Click to Email
Graphene direct growth by molecular beam epitaxy (MBE) occurs on a p-type but not n-type oxide, with resulting charge transfer and substrate-induced graphene spin polarization to > 400 K. C MBE on 10 Å p-type Co3O4(111)/Co(0001) at ~ 800 K yields layer-by-layer growth of graphene sheets in azimuthal registry. Significant charge transfer -- ~ 0.04 e-/C atom -- confined to the first 1-2 graphene layers, results in oxide reduction at the oxide/Co(0001) interface. In contrast, MBE on 10 Å n-type Cr2O3(0001)/Co(0001) under similar conditions yields only the desorption of C and lattice O, despite similar oxide lattice constants and a stronger Cr-O vs. Co-O bond strength. These results demonstrate that downward band bending at the Co3O4/Co interface enhances charge transfer and graphene formation. Upward band bending at the Cr2O3/Co interface inhibits such charge transfer. DFT electronic structure calculations show that such charge transfer leads to strong Co(II)/graphene carrier exchange interactions, yielding an enhanced magnetic moment and spin ordering temperature, in excellent agreement with experiment. Such substrate-induced graphene spin polarization makes possible a variety of spintronic devices operating at >> 300 K, without the bottleneck of spin injection, and with predicted magnetoresistance values of ~ 500% or more. The model further predicts such results for other p-type magnetic oxides, making possible high magneto-resistance voltage-switchable devices.