Graphene grown by Molecular Beam Epitaxy on Magnetic Oxides:
Towards Practical Spintronics

Jeffry A. Kelber
Department of Chemistry
University of North Texas, Denton, TX (76203)

Abstract:
High quality, low resistivity graphene grows directly in a layer by layer mode on Co3O4(111) by molecular beam epitaxy (MBE) at 1000 K [1]. Low energy electron diffraction and AFM data indicate an average domain size of ~ 1800 Å--comparable to CVD graphene on Cu –
with an incommensurate graphene/oxide interface, and graphene sheets in registry, rather than azimuthally rotated. Few layer graphene/Co3O4(111)/Co(0001) interactions result in significant graphene-to-oxide charge transfer, as determined by a C(1s) binding energy of 285 eV, and the optical π?π* resonance (5.5 eV) blue-shifted by 1 eV from graphene/SiC. This charge transfer, ~0.04 e-/carbon atom, is consistent with a sheet resistivity of 7Ω/sq, ~ 1000 times lower than graphene/SiC. Magneto-optic Kerr effect (MOKE) data show that graphene/Co3O4(111)/Co(111) trilayers exhibit antiferromagnetic hysteresis up to at least 420 K, with zero remanence magnetization [2]. In the absence of graphene, Co3O4/Co bilayers exhibit only weak paramagnetism for T>TN (40 K). There is zero remanent magnetization, and magnetic force microscopy indicates that this is due to randomized orientation of in-plane spin-polarized graphene domains [2]. The data point to strong RKKY-type interactions between graphene carriers and localized Co spins, which disrupt the ferromagnetic state of the Co substrate. These results, suggest a new type of spin-field effect transistor based on the substrate-induced coherent spin polarization of graphene conduction carriers, rather than the injection/transport of discrete spins. The potential for such devices, based on these and additional recent results on other magnetic/magnetoelectric oxides, such as chromia, will be discussed.

[1] M. Zhou, et al., J. Phys.: Cond. Matt. 24 (2012) 072201
[2] Y. Wang, et al., J. Phys.: Cond. Matt. 25 (2013) 472203

Acknowledgement Collaborations with P. Dowben, C. Binek and M. Schubert are gratefully acknowledged. This work was supported by the SRC-GRC under Task IDs 2123.001 and 2358.001, and by the C-SPIN Starnet Center.

Bio:

Jeffry A. Kelber was born in Philadelphia and attended public schools in Wheaton, IL. He obtained a B. Sc. in Chemistry from the California Institute of Technology, and a Ph.D. in Inorganic Chemistry under Prof. Galen Stucky at the University of Illinois at Champaign-Urbana. He then became a Member of Technical Staff at Sandia National Laboratories, Albuquerque, where he employed surface science techniques to look at metal polymer interactions and chemical vapor deposition processes. In 1990, he assumed a faculty position at the University of North Texas, where he is currently a Regents Professor of Chemistry. He is also the Director of the SRC/UNT joint Center for Electronic Materials Processing and Integration. His research interests are in the surface chemistry of thin film processing, and the deposition of ultrathin films for emerging electronic and spintronic applications. He has received three Inventor Recognition Awards from the Semiconductor Research Corporation and the Dougherty Award from the Texas Chapter of the American Chemical Society. He has been named a Toulouse Scholar and a Dekker Scholar by UNT. He is a member of the American Vacuum Society and the Electrochemical Society.