Improvement of spin transfer torque in asymmetric graphene devices.

A graphene lateral spin valve structure with asymmetric contacts is presented for the first time, with enhancement of spin angular momentum absorption in its receiving magnet. The asymmetric device with tunneling barrier only at the injector magnet shows a comparable spin valve signal but lower electrical noises compared to the device with two tunneling barriers. We also report experimental measurements of spin transfer torque. Assisted by an external magnetic field of 2.5 mT, spin diffusion current-induced magnetization reversal occurs at a nonlocal charge current density of 33 mA/µm(2), smaller than that needed in devices with two tunneling barriers.