Enhanced spin injection efficiency and extended spin lifetimes in graphene spin valves

Enhanced spin injection efficiency and extended spin lifetimes are achieved in graphene spin valves. Spin injection efficiency is enhanced via tunneling spin injection into graphene through an MgO barrier. A large nonlocal magetoresistance of 130 Omega is observed for a single layer graphene (SLG) spin valve at room temperature (RT) with spin injection efficiency of similar to 26-30%. Extended spin lifetimes are observed using tunneling contact to suppress the contact induced spin relaxation. In SLG, spin lifetime as long as 771 ps is observed at RT. In bilayer graphene (BLG), we observe the spin lifetime of 6.2 ns at 20 K, which is the longest value reported in any graphene spin valve. Furthermore, contrasting spin relaxation behaviors are observed in SLG and BLG, which suggests that Elliot-Yafet spin relaxation dominates in SLG at low temperatures, while Dyakonov-Perel spin relaxation dominates in BLG at low temperatures.