Spontaneous spin coherence inn-GaAs produced by ferromagnetic proximity polarization

Abstract
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.
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