Microstructure formation in electrodeposited Co–Cu/Cu multilayers with GMR effect: Influence of current density during magnetic layer deposition

Abstract

The influence of the current density applied during the deposition of the magnetic layers on the microstructure formation in electrodeposited Co-Cu/Cu multilayers and on their giant magnetoresistance (GMR) was investigated using a combination of magnetoresistance measurements, wide-angle and small-angle X-ray scattering, high-resolution transmission electron microscopy, atomic force microscopy and chemical analysis. The magnetoresistance measurements revealed that a reduction of the current density stimulates a transition from the formation of the magnetic layers with predominantly ferromagnetic character to the formation of superparamagnetic regions. As based on electrochemical considerations, it was supposed that such a change in the magnetic properties can be caused by an increased amount of Cu codeposited with Co at low current densities. It turned out from the structural studies that a pronounced segregation of Co and Cu occurs at low current densities. In accordance with their very low mutual solubility at room temperature, no atomic scale intermixing of Co and Cu could be detected. The segregation of Cu and Co was related to the fragmentation of the magnetic layers, to the enhancement of the local lattice strains, to the increase of the interface corrugations, to the partial loss of the multilayer periodicity and finally to the formation of Co precipitates in the Cu matrix.

Giant Magnetoresistance and Structure of Electrodeposited Co/Cu Multilayers: The Influence of Layer Thicknesses and Cu Deposition Potential

“…1 and 2 in order to deduce the experimental bilayer length XRD and the results are summarized in Fig. 3 Co/Cu multilayers, 26 including also data derived with the help of a more sophisticated full-profile fitting procedure 13,14 or even direct cross-sectional TEM imaging.…”

“…It should be noted that for G/P multilayers deposited at E EC Cu , the actual layer thicknesses correspond fairly well to the nominal values as determined above which was evidenced from detailed XRD studies. 13,14 However, for multilayers for which the applied Cu deposition potential is more positive than E EC Cu , the actual magnetic layer thickness will be smaller and the Cu layer thickness larger than the corresponding nominal values. The reason of this layer thickness deviation is the partial dissolution of Co atoms from the last magnetic layer during the Cu layer deposition pulse.…”

“…In general, the bilayer lengths derived from either TEM or XRD were in fairly good agreement with the nominal values, the experimental data being typically 10 to 20% higher. 13,14,[26][27][28] In order to trace out the layer thickness changes in the fourth set of multilayers, the overall composition of the multilayers also had to be determined. This analysis was carried out by energy dispersive X-ray fluorescence (EDXRF) method with an XGT-HORIBA-5200 instrument.…”

“…By looking at former reports, [5][6][7][8][9][10][11][12][13][14][15] it can be established that in most cases not completely systematic studies on layer thicknesses have been carried out for ED Co/Cu multilayers from the sulfate bath. For example, there were several studies of the GMR dependence on layer thicknesses, where one of the layer thicknesses was fixed and the other layer thickness was only varied.…”

“…Over the last two decades, numerous reports have been published on studying the GMR characteristics of ED Co/Cu multilayers from the pure sulfate bath (containing at most some buffering agents). [5][6][7][8][9][10][11][12][13][14][15] In this list of references, we have included only those works from the much larger number of reports 4 in which the ED Co/Cu multilayers were prepared from the sulfate bath at or close to the electrochemically optimized Cu deposition potential E EC Cu 5,10,16 where neither Co dissolution, nor Co codeposition can occur during the Cu pulse. These features ensure that the actual layer thicknesses will be fairly close to the nominal values and that the spacer layer will not contain magnetic Co atoms.…”