The structure, composition and magnetic properties of direct-plated fcc Co–Pt-based tubular nanostructures

Co–Pt-based tubular nanostructures were prepared by direct plating into track-etched polycarbonate templates from a single electrolyte containing a Pt-p-salt and Co-sulphamate. These tubular nanostructures, with a diameter of 200 nm and lengths up to 5 μm, were obtained with potentiostatic depositions at potentials of −1.9 V to −2.5 V, measured against a Ag/AgCl electrode for 60 min. A detailed TEM/EDS analysis showed that the tubes consisted of randomly orientated nanocrystals of an FCC Co–Pt phase and that the composition of an individual nanotube varies along its length. The formation mechanism of the Co–Pt-based tubular nanostructures can therefore be explained via partial Au-coverage of the template and the appropriate relative rates of the deposition and diffusion of the Pt and Co electro-active species, most probably assisted by hydrogen evolution. The as-deposited Co–Pt-based nanotubes, with an aspect ratio of 10, are magnetically isotropic and have a coercivity of 10 kA m−1. The easy axis of the magnetization was found to be perpendicular to the axis of the tube.