Magnetic Fe catalyst particles in the vapor-phase-grown multi-walled carbon nanotubes

Control of the magnetic Fe catalyst particle size encapsulated in multi-walled carbon nanotubes (MWNTs) was obtained by means of the vapor-phase growth employing different reaction gas flow rates. According to our structural and magnetic investigation, the magnetic encapsulation in the MWNTs consists of α-Fe core particles and interfacial Fe3C surrounding them. Characteristic α-Fe particle size dependence of the coercivity was revealed, and the coercivity as well as the anisotropy were shown to be dictated by the interfacial Fe3C.