High-temperature magnetic coercivity of CNTs filled with multi-phase Febased nanoparticles

A system of Fe-filled multiwall carbon nanotubes (MWCNT) was grown by aerosol chemical vapor deposition with three different concentrations of ferrocene as precursor catalyst. The obtained samples were thoroughly analyzed from the point of view of their morphological, microstructural and magnetic properties. It was found that ferrocene concentration did not change the MWCNTs morphology. However, it increases the number of MWCNTs containing Fe and the Fe amount in each MWCNT. The Fe is located either in form of nanorods within the inner channel of the MWCNTs or as nanoparticles of various sizes, sometimes aggregated in clusters. The magnetic results indicate the presence of different phases, identified as ?-Fe, Fe3C and Fe3O4, mostly in form of single-domain particles. A simple model of single domain non-interacting particles allows explaining the observed temperature behavior of coercivity and remanence over a wide temperature range, up to 950 K. The different ferrocene concentrations affect only the saturation magnetization but not the coercivity of the samples. As a further result, MWCNT/epoxy nanocomposites, with possible application as electromagnetic shields, were prepared by the "two factor mechanical method". The nanocomposites exhibit the same magnetic properties of the Fe-filled MWCNTs, in terms of both coercivity and hysteresis loop shape.