| AVS 60th International Symposium and Exhibition | |
| Magnetic Interfaces and Nanostructures | Tuesday Sessions |
| Session MI+EM-TuM |
| Session: | Spintronics and Magnetoelectrics |
| Presenter: | J. Kelber, University of North Texas |
| Authors: | F. Paquale, University of North Texas Y. Cao, University of North Texas H. Kasi, University of North Texas S. Gaddam, University of North Texas L. Kong, University of Nebraska-Lincoln Y. Wang, University of Nebraska-Lincoln C. Binek, University of Nebraska-Lincoln P.A. Dowben, University of Nebraska-Lincoln J. Kelber, University of North Texas |
| Correspondent: | Click to Email |
The direct growth of graphene on thin (< 50 Å) magnetic oxides on cobalt or other ferromagnetic substrates (Gr/oxide/Co) presents interesting opportunities for development of practical magnetic and magnetoelectric graphene devices. We have grown single and few layer graphene (Gr) directly on Co3O4(111)/Co(0001) by MBE, and have very recently grown graphene by e-beam-assisted deposition on Cr2O3(0001)/Co(0001). XPS data demonstrate the presence of a sp2-indicative π --> π* shakeup feature but with C(1s) peak binding energies of 284.9 (±0.2) eV for Gr/Co3O4(0001) -- significantly larger than the 284.5 eV value common for graphitic systems. This indicates significant graphene-to-oxide charge transfer. LEED images yield the expected C6v symmetry and 2.5(±0.1) Å lattice spacing for graphene, with a 2.8(±0.1) Å O-O distance at the oxide surface. All are consistent with the literature and indicate incommensurate graphene/oxide interfaces. Domain sizes of ~ 1800 Å are estimated from the LEED data for Gr/Co3O4(111), comparable to HOPG. 3 monolayer (ML) Gr/Co3O4(111)/Co(0001) exhibits room temperature resistivity 102-103 times smaller than for graphene transferred to other substrates, and consistent with strong p-type doping, as indicated by XPS. Magneto-optic Kerr effect (MOKE) results demonstrate the presence of antiferromagnetic (AF) ordering for the Gr/Co3O4(111)/Co(0001) heterostructures up to at least 420 K, with evidence of exchange interaction effects as well. No antiferromagnetic polarization is observed for Co3O4/Co films in the absence of graphene, indicating a role played by graphene in the magnetic ordering of the oxide. These results indicate the potential suitability of such films for non-local spin valves and similar devices operating at realistic device temperatures. This talk will also present results for on-going MOKE and transport measurements on graphene/Cr2O3/Co(0001) samples. The ability to apply both magnetic and electric fields to such stacks provides the potential for magnetoelectric spin-transistors and tunneling devices.
Acknowledgement: This work was supported by the Semiconductor Research Corporation under Task ID 2123.001 and by C-SPIN, a STARnet center, a Semiconductor Research Corporation program sponsored by MARCO and DARPA.