Layer thickness dependence of CPP giant magnetoresistance in individual CoNi/Cu multilayer 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 t(CoNi)=2-510 nm and that of the Cu layer thickness t(Cu)=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 t(CoNi) at fixed t(Cu) and that with t(Cu) at fixed t(CoNi) 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.