  A hybrid ferromagnet/semiconductor device is used to determine a lower bound
on the spin lifetime for conduction electrons in silicon. We use spin
precession to self-consistently measure the drift velocity vs. drift field of
spin-polarized electrons and use this electronic control to change the transit
time between electron injection and detection. A measurement of normalized
magnetocurrent as a function of drift velocity is used with a simple
exponential-decay model to argue that the lifetime obtained (~2 ns) is
artificially lowered by electronic effects and is likely orders of magnitude
higher.
