Effects of Layer Deposition Sequence on Microstructure and Magnetostatic Coupling of Spin-Valves with Amorphous CoNbZr Layer

We investigate spin-valve sandwiches with thin amorphous CoNbZr as soft layers. The magnetoresistance (MR), microstructure, and magnetostatic coupling are studied in these sandwiches with different layer deposition sequences. For the CoNbZr/Cu/Co sandwich, the CoNbZr underlayer provides a smoother surface on which smooth Cu and Co layers can subsequently grow. The Cu spacer is dense and pinholes-free, leading to a good ``spin valve'' effect with a larger MR ratio of 3.8%. For the Co/Cu/CoNbZr sandwich, however, the Cu spacer is rough and pinholes were observed, which could induce a direct ferromagnetic coupling. Correlated rougher surfaces on both the sides of the Cu spacer were also observed, giving rise to an ``orangepeel'' coupling of
about 0.105erg/cm^-2. This strong ferromagnetic coupling in Co/Cu/CoNbZr results in a lower MR ratio of 1.6%. Moreover, upon proper thermal annealing, the CoNbZr/Cu/Co has a larger MR enhancement and a superior thermal stability to 350°C due to the dense and homogenous structure in the spacer layer.