Co-Cu/Cu multilayers with Cu layer thickness ranging from 0.37 to 3.45 nm were deposited by galvanostatic/potentiostatic method from electrolytes with 5-200 mM Cu2+ concentration. The composition analysis revealed an increasing Cu content of the magnetic layers with c(Cu2+). Magnetoresistance up to 8 kOe was measured for each sample. Samples with a thin Cu layer (i.e., 0.37 nm) exhibited anisotropic magnetoresistance. At higher Cu layer thicknesses, giant magnetoresistance was observed. The higher the Cu2+ concentration, the smaller the slope of the magnetoresistance curves at low magnetic field and the higher the saturation field. Magnetoresistance curves were quantitatively separated into ferromagnetic and superparamagnetic contributions. While the ferromagnetic portion of the magnetoresistance varied with the Cu layer thickness in the same way, the superparamagnetic contribution was higher, the larger the Cu content of the magnetic layer. The size of the superparamagnetic regions decreased with increasing Cu content of the magnetic layers. The copper layer thickness dependence of the magnetoresistance properties could be elucidated by accounting for both the asymmetric nucleation of Co on Cu and vice versa and the variation of the Cu content of the magnetic layers. General conclusions on the electrodeposition of magnetic/nonmagnetic multilayers have also been drawn. (c) 2005 The Electrochemical Society.