Since the discovery by Iijima in 1991 carbon nanotubes have attracted the attention of many research groups owing to their great properties. The small size, large aspect ratio, exceptional elasticity, mechanical strength and high chemical stability render these nanostructures ideal systems which can be filled with tailored materials to address many purposes.
The possibility of filling nanotubes with ferromagnetic single-crystals of a-Fe nanowires is very attractive owing to the high saturation magnetization and high coercivity of these materials. The carbon shells provide an effective barrier against oxidation and consequently ensure long-term stability of the ferromagnetic core. These ferromagnetic-systems can be ideal candidates for many magnetic applications. For example as nano-heaters, owing to the heat dissipation generated by the reversal of the magnetic moment direction in the presence of an alternating magnetic field.
In spite of the attractive properties, the synthesis of these ferromagnetic structures is complicated by the presence of other Fe-based phases (Fe3C and g-Fe) mixed with a-Fe and by the difficulty of controlling the nanowire continuity with the conventional synthesis methods.
In this talk I will present two new approaches that allow continuous fillings of more than 90% of the nanotubes cores with a-Fe nanowires. X-ray diffraction, scanning electron microscopy and transmission electron microscopy were used to analyse the morphology and the structure of the nanowires. The magnetic properties of these nanowires are also investigated