Experimental results on a new ''spin-valve'' system for magnetoresisti
ve detection, based on epitaxial Fe/Pd bilayers grown on MgO single cr
ystals, are presented. These Fe/Pd bilayers display particularly sensi
tive magnetic properties, which are shown to result directly from the
presence of the polarized Pd interface. A magnetically hard trilayer i
s subsequently grown onto the soft Fe/Pd bilayer, forming an epitaxial
spin-valve system which displays abrupt transitions between states of
parallel and antiparallel alignment of the two magnetic layers. The f
ield sensitivity of the resistivity at low temperatures attains 0.3% p
er Oe in a Fe/Pd/Cu/Co/Cu system.