Magnetoresistance of lateral semiconductor spin valves

The magnetoresistance of two terminal lateral semiconductor spin valves with respect to varying mesa size is studied. It is shown theoretically that extended regions outside the spin-current path can act as an additional source of spin-relaxation, decreasing the magnetoresistance response. From a simplified expression of magnetoresistance derived from spin-diffusion equations, we show that it is important to etch away these extended regions for devices with channel lengths much smaller than the spin-diffusion length in order to achieve maximum magnetoresistance. Preliminary experimental data on a two terminal local spin valve are in good agreement with the theory established in this article.