Dresden 2014 – scientific programme

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O: Fachverband Oberflächenphysik

O 25: Symposium Spin Properties of Graphene (HL jointly with DS, MA, O, TT)

O 25.3: Invited Talk

Tuesday, April 1, 2014, 10:30–11:00, HSZ 02

Role of MgO barriers for spin and charge transport in Co/MgO/graphene spin-valve devices — •Bernd Beschoten — 2nd Institute of Physics and JARA-FIT, RWTH Aachen University, 52074 Aachen, Germany

We investigate the influence of MgO barriers on spin and charge transport in single (SLG) and bilayer (BLG) graphene spin-valve devices. Similar to previous studies on BLG [1], we observe a 1/µ of the spin lifetime in SLG devices. This general trend is only observed in devices with large contact resistance area products R_cA>1kΩµm². In devices with long spin lifetimes, we furthermore observe a second Dirac peak, which results from charge transport underneath the contacts. In contrast, all devices with R_cA<1kΩµm² only exhibit a single Dirac peak. Additionally, the spin lifetime is significantly reduced indicating that an additional spin dephasing occurs underneath the electrodes. In the latter devices we achieve a gradual increase of R_cA values by successive oxygen treatments. With this manipulation of the contacts both spin lifetime and amplitude of the spin signal can significantly be increased by a factor of seven in the same device. Finally, we present a new method to fabricate graphene-based lateral spin valves on hexagonal boron nitride yielding spin lifetimes above 3 ns, spin diffusion length above 10 µm and large charge carrier mobilities above 30.000 cm²/Vs.

This work was supported by DFG through FOR 912.

[1] T.-Y. Yang et al., Phys. Rev. Lett. 107, 047206 (2011).

[2] F. Volmer et al. Phys. Rev. B 88, 161405(R)(2013).