Growth and characterisation of electrodeposited Co/Cu superlattices

Ferromagnetic/non-ferromagnetic Co/Cu superlattices were grown on polycrystalline Titanium (Ti) from a single electrolyte by electrodeposition. Microstructure and magnetoresistance (MR) of the superlattices were investigated as a function of the electrolyte pH as well as the layer thicknesses. Structural characterisation by X-ray diffraction (XRD) showed that the superlattices have face-centred cubic (fcc) structure with a strong (111) texture at the studied pH levels, but the texture degree is affected by the electrolyte pH. The scanning electron microscope (SEM) studies revealed that the superlattices grown at low pH (2.0) have smoother surfaces compared to those grown at high pH (3.0). The superlattices exhibited either anisotropic magnetoresistance (AMR) or giant magnetoresistance (GMR) depending on the Cu layer thickness. The shape of MR curves changes depending on the combination of Co and Cu layer thicknesses. The superlattices with Co layers less than 3 nm and Cu layers less than 2 nm have broad and non-saturating curves, indicating the predominance of a superparamagnetic contribution, possibly due to the discontinuous nature of the ferromagnetic (Co) layer. For superlattices with the same bilayer and total thicknesses, the GMR magnitude decreased as the electrolyte pH increased. Besides possible structural differences such as the texture degree and the surface roughness, this may arises from the variation in the Cu content of the ferromagnetic layers caused by the electrolyte pH.