Giant magnetoresistance and structure of electrodeposited Co/Cu multilayers: the influence of layer thicknesses and Cu deposition potential

摘要

The giant magnetoresistance (GMR) and structure was investigated forelectrodeposited Co/Cu multilayers prepared by a conventionalgalvanostatic/potentiostatic pulse combination from a pure sulfate electrolytewith various layer thicknesses, total multilayer thickness and Cu depositionpotential. X-ray diffraction (XRD) measurements revealed superlattice satellitereflections for many of the multilayers having sufficiently large thickness (atleast 2 nm) of both constituent layers. The bilayer repeats derived from thepositions of the visible superlattice reflections were typically 10-20% higherthan the nominal values.The observed GMR was found to be dominated by themultilayer-like ferromagnetic (FM) contribution even for multilayers withoutvisible superlattice satellites. There was always also a modestsuperparamagnetic (SPM) contribution to the GMR and this term was the largestfor multilayers with very thin (0.5 nm) magnetic layers containg apparently asmall amount of magnetically decoupled SPM regions. No oscillatory GMR behaviorwith spacer thickness was observed at any magnetic layer thickness. Thesaturation of the coercivity as measured by the peak position of the MR(H)curves indicated a complete decoupling of magnetic layers for large spacerthicknesses. The GMR increased with total multilayer thickness which could beascribed to an increasing SPM contribution to the GMR due to an increasingsurface roughness, also indicated by the increasing coercivity. For multilayerswith Cu layers deposited at more and more positive potentials, the GMRFM termincreased and the GMRSPM term decreased. At the same time, a correspondingreduction of surface roughness measured with atomic force microscopy indicatedan improvement of the multilayer structural quality which was, however, notaccompanied by an increase of the superlattice reflection intensities.