Multiwall carbon nanotubes continuously filled with micrometre-length ferromagnetic α-Fe nanowires

Carbon nanotubes filled with continuous crystalline nanowires of nanometre-scale diameter and micrometre-scale length of the ferromagnetic phase α-Fe were produced with a new chemical vapour deposition method. We report a new two-stage approach, a perturbed-vapour method of synthesis followed by a post-synthesis heat treatment that produces multiwall carbon nanotubes filled with at least 19 micrometre-length nanowires of α-Fe. Previously reported synthesis routes use steady-state conditions to guarantee nanowire continuity but result only in small (less than one-micrometre length) nanowires comprising isolated or mixed phases of either α-Fe, Fe3C, or γ-Fe. Here flower-like clusters of carbon nanotubes continuously filled with α-Fe were produced by perturbation of a laminar ferrocene (Fe(C5H5)2) vapour flow in a conventional horizontal chemical vapour deposition reactor. Single-phase filling was achieved by a post-synthesis annealing at 500 °C for 15 h in Ar flow. Electron microscopy studies revealed the high quality of the structural integrity of both nanotubes and encapsulated nanowires. These nanostructures possess a high coercivity of 580 Oe and a very high saturation magnetization of 189.5 emu/g comparable with bulk α-Fe.