Spontaneous Spin Coherence in n-GaAs Produced by Ferromagnetic Proximity   Polarization
  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. 
R. J. Epstein, I. Malajovich, R. K. Kawakami, Y. Chye, M. Hanson, P.   M. Petroff, A. C. Gossard, and D. D. Awschalom