  Using a microfabricated, p-type GaAs Hall bar, is it shown that the combined
application of co-planar electric and magnetic fields enables the observation
at 50 K of spatial oscillations of the photoluminescence circular polarization
due to the precession of drifting spin-polarized photoelec- trons. Observation
of these oscillations as a function of electric field E gives a direct
measurement of the minority carrier drift mobility and reveals that, for E =
800 V/cm, spin coherence is preserved over a length as large as 25{\mu}m.
