Giant magnetoresistance and oscillatory exchange coupling in disordered Co/Cu multilayers

We measured the exchange coupling strength and magnetoresistance for multilayers of Co/Cu grown by sputtering. The samples have (111) texture with a grain size of about 140 Angstrom. Their mosaic spread, determined by high-angle x-ray rocking curves in triple-axis geometry, is as large as 16 degrees, suggesting the description disordered. The magnetoresistance oscillates as a function of the Cu thickness and reaches 70% at room temperature with near zero remanence at the first antiferromagnetic peak. These results indicate that a sufficient condition for oscillatory exchange coupling with a period of similar to 10 Angstrom is a well defined separation between the magnetic layers. We also measured the exchange coupling strength as a function of the magnetic layer thickness and found no oscillations. The measured saturating magnetic field is accurately described by the 'orange-peel' coupling effect.