  A time domain approach to probe hot carrier-induced spin dynamics is
demonstrated. The experiments are performed in epitaxial Au/Fe/MgO(001), where
spin-polarized hot carriers are excited in the Fe layer by 35 fs laser pulses.
They propagate to the Au surface where the transient spin polarization is
detected by magneto-induced second harmonic generation. Different energies of
majority and minority hot carriers excited in the exchange-split Fe band
structure lead to their spindependent lifetimes in Au. Accordingly, two
spin-polarized current contributions which propagate superdiffusively at
different velocities result in a spin current pulse of about 100 fs duration.
