Diameter-modulated ferromagnetic CoFe nanowires

Abstract

Highly ordered nanoporous anodic aluminium oxide templates with uniform or periodically modulated pore diameters have been fabricated by the hard-pulse anodization technique. Straight and diameter-modulated CoFe nanowires with diameters of 60 nm and 60/120 nm, respectively, were AC-pulse electrodeposited into the templates. A comparison of magnetisation curves of the two types of nanowires show a typical coercivity (μ0Hc) of 74 mT and squareness (SQ) of 92% for the modulated wires, which are significantly squarer but have 12% lower coercivity compared to the 60 nm straight CoFe wires (μ0Hc = 84 mT, SQ = 60%). The difference is attributed to magnetostatic interactions between the segments due to the stray field of the modulated wires. Diameter modulation is an attractive way of producing soft magnetic nanowires with a controllable hysteresis loop shape. The time required for the nanoporous template fabrication by hard-pulse anodization is typically one tenth of that needed for conventional template fabrication methods, hence making it suitable for large-scale nanowire production.