Synthesis and Characterization of Highly Ordered Cobalt–Magnetite Nanocable Arrays

Abstract Magnetically tunable, high‐density arrays of coaxial nanocables within anodic aluminum oxide (AAO) membranes have been synthesized. The nanocables consist of magnetite nanowires surrounded by cobalt nanotube sheaths and cobalt nanowires surrounded by magnetite nanotube sheaths. These materials are a combination of separate hard (Co) and soft (Fe₃O₄) magnetic materials in a single nanocable structure. The combination of two or more magnetic materials in such a radial structure is seen as a very powerful tool for the future fabrication of magnetoresistive, spin‐valve and ultrafast spin‐injection devices with nonplanar geometries. The nanocable arrays were prepared using a supercritical‐fluid inclusion process, whereby the nanotube was first deposited onto the pore walls of the nanoporous membranes and subsequently filled with core material to form coaxial nanocables. In essence, this paper describes a technique for placing novel magnetic technologies into well‐defined building blocks that may ultimately lead to new multifunctional devices, such as spin valves and high‐density magnetic storage devices.