Preparation and magnetoresistance characteristics of electrodeposited Ni-Cu alloys and Ni-Cu/Cu multilayers

Galvanostatic electrodeposition was used to produce Ni-Cu alloys and Ni(81)Cu(19)/Cu multilayers by direct current (dc) plating and two-pulse plating, respectively, from a sulfate/citrate electrolyte. For the de-plated Ni-Cu alloys, the deposition rate and the alloy composition were established as a function of the deposition current density, from which the appropriate deposition parameters for the constituent sublayers of the multilayers could be established. By measuring the resistivity at room temperature in magnetic fields up to H = 7 kOe, anisotropic magnetoresistance (AMR) was found for Ni(81)Cu(19) electrodeposits, whereas both giant magnetoresistance (GMR) and AMR contributions were observed for most Ni(81)Cu(19)/Cu multilayers. Finally, Ni-Cu alloys were also prepared by conventional pulse plating, varying the length of the deposition pulse (on-time) with constant separation (off-time) between the pulses. Clear evidence of a GMR contribution also appeared in these pulse plated Ni-Cu alloys which may be explained by the formation of a Cu enriched layer between the ferromagnetic layers deposited during the cathodic pulses. A quartz crystal microbalance experiment confirmed that an exchange reaction takes place during the off-time. These findings provide useful information on the formation mechanism of multilayers by the two-pulse plating technique. (C) 2000 The Electrochemical Society. S0013-4651(99)06-106-6. All rights reserved.