Shape-dependent magnetic properties of gradient-diameter Co nanowire arrays

Magnetic nanowire arrays grown in anodized alumina templates offer a fertile ground to investigate the interplay among the exchange interaction, dipolar interaction, and magnetocrystalline anisotropy. In this study, we have successfully fabricated Co nanowire arrays with gradient diameter while maintaining the nanowire separation. Consequently, we are able to obtain nanowire arrays with dominant exchange interaction at one end with small nanowire dimeter and dominant dipolar interaction at the other with large nanowire diameter. These samples show very different magnetic properties from those observed in magnetic nanowire arrays with uniformly diameter. The easy magnetization axis, coercivity, saturation field, and reversal processes are all controlled collectively by both ends of the nanowires, which cannot be viewed as the combination of magnetic nanowire arrays with thin and thick diameters.