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 observed 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 interfaces, as probed by real-time RHEED techniques, HRTEM, and spin-echo NMR. We propose that the lowered dimensionality of the structure leads to an enhancement of the scattering of conduction electrons from paramagnetic interfaces obeying a Langevin-like saturation at very high fields, well beyond the switching field of the Co layers. Scaling between the GMR and thermopower measurements suggests that a spin-dependent density of states at the Co-Cu interfaces is responsible for the observed magnetotransport behavior in these samples, rather than antiferromagnetically coupled Co layers.