Microstructure and Giant magnetoresistance of electrodeposited Co-Cu/Cu multilayers

Direct current plating, pulse plating, two-pulse plating, and reverse pulse plating were used to produce electrodeposited Cb-Cu alloys and Co-Cu/Cu multilayers under galvanostatic control from an electrolyte containing CoSO sub 4 and CuSO sub 4 . Atomic force microscopy, X-ray diffraction, and transmission electron microscopy were used to study the sample structure and morphology. Direct current plating resulted in a Co sub 95 Cu sub 5 alloy with nearly equal amounts of face-centered cubic (fcc) and hexagonal close packed phases, while all pulsed current methods yielded multilayers with fcc structure. Giant magnetoresistance (GMR) behavior was observed in the multilayers with a maximum magnetoresistance (MR) ratio of about 9% as measured at 8 kOe. The shape of the MR curves and the magnitude of the GMR were very similar, regardless of the sign of the current between the Co deposition pulses. The results of structural studies also confirmed the formation of a multilayer structure for each pulsed electrodeposition mode. The conclusion was that the spontaneous exchange reaction between Co and Cu exp 2+ is responsible for the formation of a pure Cu layer even under reverse pulse plating conditions. The GMR of the multilayer deposits decreased with increasing bilayer number, due to the deterioration of the microstructure as the deposit grew.