  The effect of nuclear spins in Fe/GaAs all-electrical spin-injection devices
is investigated. At temperatures below 50 K, strong modifications of the
non-local spin signal are found that are characteristic for hyperfine coupling
between conduction electrons and dynamically polarized nuclear spins. The
perpendicular component of the nuclear Overhauser field depolarizes electron
spins near zero in-plane external magnetic field, and can suppress such
dephasing when antialigned with the external field, leading to satellite peaks
in a Hanle measurement. The features observed agree well with a Monte Carlo
simulation of the spin diffusion equation including hyperfine interaction, and
are used to study the nuclear spin dynamics and relate it to the spin
polarization of injected electrons.
