  The giant magnetoresistance (GMR) and structure was investigated for
electrodeposited Co/Cu multilayers prepared by a conventional
galvanostatic/potentiostatic pulse combination from a pure sulfate electrolyte
with various layer thicknesses, total multilayer thickness and Cu deposition
potential. X-ray diffraction (XRD) measurements revealed superlattice satellite
reflections for many of the multilayers having sufficiently large thickness (at
least 2 nm) of both constituent layers. The bilayer repeats derived from the
positions of the visible superlattice reflections were typically 10-20% higher
than the nominal values.The observed GMR was found to be dominated by the
multilayer-like ferromagnetic (FM) contribution even for multilayers without
visible superlattice satellites. There was always also a modest
superparamagnetic (SPM) contribution to the GMR and this term was the largest
for multilayers with very thin (0.5 nm) magnetic layers containg apparently a
small amount of magnetically decoupled SPM regions. No oscillatory GMR behavior
with spacer thickness was observed at any magnetic layer thickness. The
saturation of the coercivity as measured by the peak position of the MR(H)
curves indicated a complete decoupling of magnetic layers for large spacer
thicknesses. The GMR increased with total multilayer thickness which could be
ascribed to an increasing SPM contribution to the GMR due to an increasing
surface roughness, also indicated by the increasing coercivity. For multilayers
with Cu layers deposited at more and more positive potentials, the GMRFM term
increased and the GMRSPM term decreased. At the same time, a corresponding
reduction of surface roughness measured with atomic force microscopy indicated
an improvement of the multilayer structural quality which was, however, not
accompanied by an increase of the superlattice reflection intensities.

Materials Science