Magnetic behavior of iron-filled multiwalled carbon nanotubes

Using vibrating-sample magnetometry, magnetic properties of iron-filled multiwalled carbon nanotubes have been investigated. The field dependence of dc magnetization at high magnetic fields suggests that these tubes behave as a one-dimensional exchange-coupled ferromagnetic system. At 5 K, the saturation magnetization (M-S) of the nanowires is found to be 85 emu/g, which is much less than the expected bulk value similar to 210 emu/g. The observed exchange bias, in spite of the small fraction of gamma-Fe in our samples, implies that gamma-Fe may not be the only antiferromagnetic component responsible for the exchange bias in these Fe-filled carbon nanotubes. Quantitative study on the temperature dependence of saturation magnetization, remanent magnetization and coercivity has been carried out. (C) 2005 American Institute of Physics.