Iron filled carbon nanotubes grown on substrates with thin metal layers and their magnetic properties

The thermal decomposition of ferrocene combined with a catalyst-assisted structuring of a Si-substrate surface is a favourable way to produce Fe-filled carbon nanotubes in good quality and in high yields. In this work we have studied the growth of such aligned filled nanotubes on iron and cobalt pre-coated Si-substrates and their dependence on the deposition time. The nanotube diameter depends on the used catalyst metal on the substrate surface. Magnetization measurements were carried out perpendicular (along tube axis) and parallel to the substrate and show excellent coercivities, a strong uniaxial anisotropy (ratios of H_c,per/H_c,par up to 6) and high saturation magnetization moments per substrate square. The magnetic behavior has been also interpreted as a function of deposition time and of the catalyst metal on the substrate. These investigations were complemented by X-ray diffraction, which revealed a majority fraction of α-Fe and a small amount of Fe₃C.