Dresden 2011 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 81: Graphene: Transport

HL 81.3: Vortrag

Donnerstag, 17. März 2011, 15:00–15:15, POT 151

Spin Transport and Spin Precession in Bilayer Graphene with Transparent and Tunneling Ferromagnetic Contacts — •Bastian Birkner, Jonathan Eroms, and Dieter Weiss — Institut für Experimentelle und Angewandte Physik, Universität Regensburg, 93040 Regensburg, Germany

We achieved electrical spin injection with a DC current from a
ferromagnetic material (Co) into bilayer graphene with transparent and with tunneling contacts. The approximately 1.4 nm thick AlOx tunnel barrier is produced by depositing Al over the entire sample at 180 K and subsequent oxidation at room temperature. AFM pictures reveal that the Al deposition at low temperature leads to a homogenous tunnel barrier. The I-V-characteristics of the Co/AlOx/graphene junction show non-linear behavior suggesting the absence of pinholes. For both, transparent and tunneling contacts we obtain a clear spin signal in a non-local four terminal scheme 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) which confirms that the non-local spin signal originates from spin injection and spin transport. Fitting of these Hanle curves yields the spin relaxation time and length as well as the spin injection efficiency. By comparing the results for transparent and tunneling contacts we find that the tunnel barrier enhances the spin signal by a factor 100 and the spin injection efficiency from 1.7 percent to 5 percent.