Effect of Current and Potential Waveforms on GMR Characteristics of Electrodeposited Ni(Cu)/Cu Multilayers

In a previous paper [W. R. A. Meuleman, S. Roy, L. Peter, and I. Varga, J. Electrochem. Soc., 149, C479 (2002)], the electrodeposition of Ni(Cu)/Cu multilayers from a citrate electrolyte has been discussed. In the present work, an X-ray diffraction (XRD) study and the magnetoresistance characteristics of the same multilayers are described. For Cu layer thicknesses above about 2 nm, satellite reflections due to multilayer periodicity could be observed. The grain sizes as deduced from the broadening of the XRD lines were between 10 and 15 nm. A clear giant magnetoresistance (GMR) behavior was observed at Cu thicknesses above 2 nm for the constant current/constant potential series where galvanostatic and potentiostatic control was used for the deposition of the magnetic and nonmagnetic layer, respectively. However, the maximum GMR at 8 kOe was around -0.3% only. For the constant current/relaxation/constant current series in which both layers were deposited under galvanostatic control with a zero current interval in between, only a very weak indication for the GMR contribution could be detected besides the dominating anisotropic magnetoresistance. Interface intermixing due to the Ni vs. Cu exchange reaction, electrolyte pH, (111) orientation of the deposit, and very small crystallite sizes have been considered as possible sources leading to the poor GMR.