AN ALTERNATE ROUTE TO GIANT MAGNETORESISTANCE IN MBE-GROWN CO-CU SUPERLATTICES

Co-Cu superlattices grown by MBE in the (111) orientation show weak or nonexistent interlayer exchange coupling, yet several groups have obs erved large high-field magnetoresistance signals in excess of 30%. In the present work, we address some of the questions relating to GMR and the interlayer coupling by studying samples with atomically abrupt in terfaces, as probed by real-time RHEED techniques, HRTEM, and spin-ech o NMR. We propose that the lowered dimensionality of the structure lea ds to an enhancement of the scattering of conduction electrons from pa ramagnetic interfaces obeying a Langevin-like saturation at very high fields, well beyond the switching field of the Co layers. Scaling betw een the GMR and thermopower measurements suggests that a spin-dependen t density of states at the Co-Cu interfaces is responsible for the obs erved magnetotransport behavior in these samples, rather than antiferr omagnetically coupled Co layers.