Topological coupling in spin valve type multilayers

The origin and the effect of topological coupling induced by interfacial roughness in spin valve type multilayers have been investigated. The upper bound of the coupling field, which is scale invariant, is predicted by a simplified model using a uniform magnetization approximation. Macroscopic sandwich structures ("macrosteps") of various complexity were fabricated to test these predictions. The coupling field was determined from the shift of the "free layer" B-H loop, or the difference in apparent coercivities. The dependence of the magnitude and the sign of the coupling on the characteristics of the roughness was measured. Implications for real spin valve films and devices are discussed, as well as the potential application of the "macrosteps", or artificial roughness, to provide desired coupling between films.