Long Spin Diffusion Length in Few-Layer Graphene Flakes

We report a spin valve with a few-layer graphene flake bridging highly spin-polarized ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_{3}$ electrodes, whose surfaces are kept clean during lithographic definition. Sharp magnetic switching is verified using photoemission electron microscopy with x-ray magnetic circular dichroism contrast. A naturally occurring high interfacial resistance $\ensuremath{\sim}12\text{ }\text{ }\mathrm{M}\mathrm{\ensuremath{\Omega}}$ facilitates spin injection, and a large resistive switching ($0.8\text{ }\text{ }\mathrm{M}\mathrm{\ensuremath{\Omega}}$ at 10 K) implies a $70--130\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ spin diffusion length that exceeds previous values obtained with sharp-switching electrodes.