  We present an ab initio calculation of the k and spin-resolved electronic
lifetimes in the half-metallic Heusler compounds Co(2)MnSi and Co(2)FeSi. We
determine the spin-flip and spin-conserving contributions to the lifetimes and
study in detail the behavior of the lifetimes around states that are strongly
spin-mixed by spin-orbit coupling. We find that, for non-degenerate bands, the
spin mixing alone does not determine the energy dependence of the (spin-flip)
lifetimes. Qualitatively, the lifetimes reflect the lineup of electron and hole
bands. We predict that different excitation conditions lead to drastically
different spin-flip dynamics of excited electrons and may even give rise to an
enhancement of the non-equilibrium spin polarization.
