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HL: Fachverband Halbleiterphysik

HL 81: Graphene: Transport incl. Spin Physics and Magnetic Fields I

HL 81.4: Vortrag

Donnerstag, 29. März 2012, 15:45–16:00, ER 270

Spin transport and relaxation in single and bilayer graphene — •Bastian Birkner, Daniel Pachniowski, Dieter Weiss, and Jonathan Eroms — Institute for Experimental and Applied Physics, University of Regensburg, 93040 Regensburg, Germany

We achieved electrical spin injection with a DC current from a
ferromagnetic material (Co) into both single layer graphene (SLG) and bilayer graphene (BLG). In order to circumvent the conductivity mismatch problem a thin AlOx tunnel barrier is placed in between graphene and the ferromagnetic contacts. This AlOx layer is produced by depositing Al atoms over the entire sample at 180 K and subsequent oxidation at room temperature. For both SLG and BLG, we obtain a clear switching of the non-local magnetoresistance whose sign depends on the magnetization orientation (parallel/antiparallel) of the ferromagnetic electrodes. By applying a perpendicular magnetic field we also detect spin precession (Hanle effect). Fitting of these Hanle curves yields the spin relaxation time and the spin injection efficiency as well as the spin diffusion constant. The latter is nearly identical with the charge diffusion constant in SLG. For BLG this is also valid if one considers a realistic band structure with a bandgap. Furthermore we find by analyzing the relationship between spin and momentum scattering that the Elliot-Yafet spin relaxation mechanism dominates in SLG at low temperature. In contrast to this result, we find a opposite behavior of the temperature dependence of the spin relaxation time and the diffusion constant which suggests the importance of the Dyakonov-Perel mechanism in BLG.