CPP-GMR performance of electrodeposited metallic multilayered nanowires with a wide range of aspect ratios

Abstract

Effect of the diameter on the CPP-GMR performance of electrodeposited Co/Cu multilayered nanowires was systematically investigated using our home-made anodized aluminum oxide (AAO) templates with the nanochannel diameter ranging from 35 to 130 nm. The nanochannel diameter was precisely controlled by tuning the anodization voltage ranging from 20 to 110 V. The Co/Cu multilayered nanowires with the aspect ratio of ~1000 were synthesized in the AAO nanochannels by applying a rectangular pulsed potential electrodeposition technique using an acidic aqueous solution containing Co2+ and Cu2+ ions. An ideal alternating Co/Cu multilayered structure with each layer thickness of several nanometers was clearly observed in the nanowires with the diameter ranging from 35 to 95 nm. The multilayered nanowires with the diameter ranging from 35 to 70 nm were spontaneously magnetized in the axial direction due to the preferential crystal orientation of hcp-Co (002) which was induced by the magnetic shape anisotropy. With decreasing the diameter down to 35 nm, the coercivity increased up to 1.37 kOe while the squareness reached 0.73 at the diameter of 50 nm. The CPP-GMR value reached 23.4% at room temperature in the Co/Cu multilayered nanowires with the diameter of 70 nm.