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We report on a systematic study of contact-induced spin relaxation in gated graphene nonlocal spin valves. We demonstrate the enhancement of the nonlocal magnetoresistance (ΔRNL) as the Co/AlOx/graphene interface resistance increases relative to the graphene spin resistance. We measure Hanle precession at many gate voltages on 14 separate spin-valve devices fabricated from graphene grown by chemical vapor deposition (CVD). These measurements are compared by normalizing ΔRNL to the ideal limit of large contact resistance, and the result is shown to be consistent with isotropic contact-induced spin relaxation caused by spin current flowing from the graphene into the Co contacts. After accounting for this source of spin relaxation, we extract spin lifetimes of up to 600 ps in CVD graphene with a gate-voltage dependence which can be described by a combination of both Elliott-Yafet and D'yakonov-Perel' spin-relaxation mechanisms.
Bibliographical noteFunding Information:
This work was supported by the National Science Foundation under Grant No.ECCS-1124831, the Nanoelectronics Research Initiative of the Semiconductor Research Corporation (SRC), and C-SPIN, a SRC STARnet center sponsored by MARCO and DARPA. Portions of this work were carried out at the College of Science and Engineering Characterization Facility, University of Minnesota (UMN), which has received capital equipment funding from the NSF through the UMN MRSEC program under Grant No.DMR-1420013. Device fabrication was carried out in the Minnesota Nano Center, which receives partial support from the NSF through the National Nanotechnology Coordinated Infrastructure (NNCI).
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- Period 3