  We report on transport measurements on Nb/Al/Gd/Al/Nb junctions.Bulk
Gadolinium is a weakly polarized ferromagnet (5-7%), and is present in the
junction in granular form (superparamagnet). We show that Andreev reflection is
strongly enhanced by a weak polarization, obtained by applying an external
magnetic field. A new model is proposed that accounts for this effect. The
transport is described in terms of ``hot'' carriers that experience Zeeman
splitting due to the spin polarized background. The Landauer formula is
$G=(4e^2)/h A(h_b)$, $h_b$ being the exchange field at the grain boundary, and
A(E) the Andreev current coefficient, that increases with E for resistive
junctions.
