Diffusion of spins in GaAs in the presence of a strongly spatially varying local magnetic field

We report on the effect of a localized, strongly inhomogeneous magnetic field on the behavior of spins in GaAs. Such magnetic fields can provide spatially resolved information regarding spin diffusion, relaxation and precession. The sample in our experiments is a 2 micron thick n-GaAs (3e16 cm$^{-3}$, Si doped) epitaxial membrane. A circularly polarized pump beam injects the spins into the membrane. The local magnetic field is provided by a micro-magnetic particle mounted on a commercial AFM cantilever. Spin-polarized photoluminescence is then used to measure the Hanle effect. The changes in the Hanle response as a function of the magnetic tip position provide information regarding the microscopic environment experienced by the spins. We also present numerical analysis of the spin diffusion equation for our experimental conditions.