We investigate spin relaxation in graphene spin valves and observe strongly contrasting behavior for single layer graphene (SLG) and bilayer graphene (BLG). In SLG, the spin lifetime ({\tau}s) varies linearly with the momentum scattering time ({\tau}p) as carrier concentration is varied, indicating the dominance of Elliot-Yafet (EY) spin relaxation at low temperatures. In BLG, {\tau}s and {\tau}p exhibit an inverse dependence, which indicates the dominance of Dyakonov-Perel spin relaxation at low temperatures. The different behavior is due to enhanced screening and/or reduced surface sensitivity of BLG, which greatly reduces the impurity-induced EY spin relaxation.
@article{arxiv.1012.3435,
title = {Spin Relaxation in Single Layer and Bilayer Graphene},
author = {Wei Han and Roland K. Kawakami},
journal= {arXiv preprint arXiv:1012.3435},
year = {2011}
}