  It has been shown previously for electrodeposited Co/Cu multilayers that the
single-bath electrodeposition process can be optimized from an electrochemical
point of view in order to avoid unwanted Co dissolution and incorporation of Co
in the non-magnetic layer during the Cu deposition pulse. In the present work,
electrodeposition of Ni-Co/Cu multilayers has been studied to clarify if the
same optimization method is appropriate when two magnetic elements are present
and if this potential results in the largest giant magnetoresistance (GMR) for
the particular alloy system studied. For this purpose, several Ni-Co/Cu
multilayers were prepared by varying the deposition potential of the Cu layer.
The composition analysis of the deposits showed that the Ni:Co ratio exhibits a
minimum as a function of the Cu deposition potential, which can be explained by
considering both the dissolution of Co and the mass transport of the reactants.
Both the saturation GMR value and the intensity of the satellite peaks in the
X-ray diffractograms were highly correlated with the resulting surface
roughness of the deposits which was strongly varying with the Cu deposition
potential. Higher GMR values, lower saturation fields and more perfect
multilayer structure were observed for sufficiently positive Cu deposition
potentials only which enabled a partial Co dissolution resulting in a reduced
surface roughness. The results draw attention to the complexity of the
optimization procedure of the deposition of multilayers with several alloying
components.
