Hot-electron transport in Co/Cu/Co trilayer films has been studied in the e
nergy range from 1.0 to 2.0 eV using ballistic electron magnetic microscopy
. Both the spin-dependent attenuation lengths of Co and the cumulative pola
rizing effects of spin-dependent tunneling and transmission across a Co/Cu
interface have been determined. For very thin (a few Angstrom) Co layers, t
he latter effects result in a weakly majority-spin polarized electron beam
above similar to 1.3 eV and a minority-spin polarized beam below similar to
1.2 eV. For thicker Co layers the transmitted beam is always majority-spin
polarized.