Interface intermixing and magnetoresistance in Co/Cu spin valves with uncoupled Co layers

Abstract

The interpretation of experiments on the effect of interface intermixing on the giant magnetoresistance (GMR) effect in antiferromagnetic-coupled multilayers can be complicated by the fact that interface intermixing also changes the coupling strength; therefore, we have grown an artificially intermixed region in Co/Cu spin valves with uncoupled Co layers. The structure we used was a newly engineered spin valve composed of 100 Å Co+6 Å Ru+25 Å Co+40 Å Cu+100 Å Co. Here the Ru layer provides an antiparallel alignment of the Co layers and the Cu layer decouples the upper two Co layers. An intermixed CoCu region has been grown at the Cu/Co interface and in some cases also at the Co/Cu interface by alternately sputtering 1 Å Co and 1 Å Cu. X-ray measurements confirm the existence of an intermixed region, although no reduction of magnetic moment is observed as is reported for homogeneous sputtered Co0.5Cu0.5 alloys. This indicates the existence of Co clusters in the intermixed regions. There is no difference in GMR between an intermixed layer of thickness t at one Co/Cu interface or two intermixed layers of thickness t/2 at both Co/Cu interfaces. Thus, it seems that the total thickness of the intermixed regions is decisive for the magnitude of the GMR. Because G, ΔG, and ΔG/Gap all show a gradual decrease when the nominal thickness of the intermixed region increases from 0 to 36 Å, this indicates that there is no strong spin-dependent scattering in this region. This is in agreement with calculations on a model bilayer Co/Cu/Co with the Camley–Barnas model.