Giant magnetoresistance (GMR) effect of $\mathrm{Co}\mathrm{Ni}∕\mathrm{Cu}$ 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 $t_{\mathrm{Co}\mathrm{Ni}}=2–510\mathrm{nm}$ and that of the Cu layer thickness $t_{\mathrm{Cu}}=4.2–42\mathrm{nm}$, the maximum value of CPP-GMR change observed in the $\mathrm{Co}\mathrm{Ni}∕\mathrm{Cu}$ nanowires was 23% at room temperature. The variation of the CPP-GMR with $t_{\mathrm{Co}\mathrm{Ni}}$ at fixed $t_{\mathrm{Cu}}$ and that with $t_{\mathrm{Cu}}$ at fixed $t_{\mathrm{Co}\mathrm{Ni}}$ 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 $\mathrm{Co}\mathrm{Ni}∕\mathrm{Cu}$ nanowires are also discussed.

• Received 24 December 2006

DOI:https://doi.org/10.1103/PhysRevB.75.134404