High coercivity of iron-filled carbon nanotubes synthesized on austenitic stainless steel

Multiwalled carbon nanotubes synthesized directly on austenitic stainless steel result in being filled with pure iron nanoparticles. X-ray diffraction shows that the nanoparticles are either in the gamma- or alpha-phase, although iron in the original alloy is in gamma-phase because of the presence of nickel. This phase transformation is due to the selective extraction of iron, performed by carbon nanotubes during their growth. A high coercivity of iron-filled carbon nanotubes is measured although the starting steel is paramagnetic. The presence of the cc-phase, the magnetic anisotropy and the single domain character of the Fe nanoparticles explain their magnetic behavior. (C) 2011 Elsevier Ltd. All rights reserved.