Local control of spin flow in weak magnetic fields
  We demonstrate that optical illumination strongly influences spin transport in n-type GaAs. Specifically, increasing the power density of optical spin pumping results in a significant expansion of the spin diffusion profile. A further means of manipulation is the application of a weak transverse magnetic field, which strongly increases spin flow out of the excitation spot. These effects are directly monitored in spin imaging experiments and spatially resolved Hanle measurements. 
J.-H. Quast, G. V. Astakhov, W. Ossau, L. W. Molenkamp, J. Heinrich,   S. Hofling, A. Forchel