  We find that photoexcited electrons in an n-GaAs epilayer rapidly (< 50 ps)
spin-polarize due to the proximity of an epitaxial ferromagnetic metal.
Comparison between MnAs/GaAs and Fe/GaAs structures reveals that this coherent
spin polarization is aligned antiparallel and parallel to their magnetizations,
respectively. In addition, the GaAs nuclear spins are dynamically polarized
with a sign determined by the spontaneous electron spin orientation. In
Fe/GaAs, competition between nuclear hyperfine and applied magnetic fields
results in complete quenching of electron spin precession.
