Layer thickness dependence of CPP giant magnetoresistance in individualCoNi∕Cumultilayer nanowires grown by electrodeposition

Giant magnetoresistance GMR effect of CoNi/Cu nanowires grown by electrodeposition using an array of parallel through holes in anodized alumina membranes was studied in the current-perpendicular-to-plane CPP geometry as a function of the CoNi and Cu layer thicknesses. The CPP-GMR measurements were carried out by making a point contact with individual nanowires using a metallic plunger tip. In the range of the CoNi layer thickness tCoNi=2–510 nm and that of the Cu layer thickness tCu=4.2–42 nm, the maximum value of CPP-GMR change observed in the CoNi/Cu nanowires was 23% at room temperature. The variation of the CPP-GMR with tCoNi at fixed tCu and that with tCu at fixed tCoNi is discussed in terms of the series-resistor model and the Valet-Fert model for CPP-GMR. The effects of various factors such as superparamagnetism in very thin CoNi layers and dipole-dipole interactions between CoNi layers on the CPP-GMR of CoNi/Cu nanowires are also discussed.