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 Co-Cu alloys and Co-Cu/Cu mu ltilayers under galvanostatic control from an electrolyte containing CoSO4 and CuSO4. Atomic force microscopy, X-ray diffraction, and transmission ele ctron microscopy were used to study the sample structure and morphology. Di rect current plating resulted in a CO95Cu5 alloy with nearly equal amounts of face-centered cubic (fcc) and hexagonal close packed phases, while all p ulsed current methods yielded multilayers with fee structure. Giant magneto resistance (GMR) behavior was observed in the multilayers with a maximum ma gnetoresistance (MR) ratio of about 9% as measured at 8 kOe. The shape of t he 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 st ructural studies also confirmed the formation of a multilayer structure for each pulsed electrodeposition mode. The conclusion was that the spontaneou s exchange reaction between Co and Cu2+ is responsible for the formation of a pure Cu layer even under reverse pulse prating conditions. The GMR of th e multilayer deposits decreased with increasing bilayer number, due to the deterioration of the microstructure as the deposit grew. (C) 2001 The Elect rochemical Society. All rights reserved.