Authors: N. Aguiló-Aguayo, J. García-Céspedes, E. Pascual, E. Bertran
Affilation: IN2UB, Universitat de Barcelona, Spain
Pages: 985 - 989
Keywords: carbon nanotubs, magnetic properties, superparamagnetism, ZFC-FC
Magnetic properties of iron-filled multiwalled carbon nanotubes have been investigated. Hysteretic and temperature dependent magnetic responses reveal a superparamagnetic behaviour at temperatures below 150ºC. The saturation magnetization of the nanowires at 5K is found to be 198 emu/g, slightly different from the expected bulk value 210 emu/g, due to the presence of a small fraction of Fe3C in our samples. Analysis of field-cooled (FC) and the zero-field-cooled (ZFC) curves show a high magnetic anisotropy of the nanowires. Langevin function has been fitted using data at 300K. The average domain size estimated has been corresponding to spherical domains with radius ~5 nm, below the value from TEM observations (radius < 20 nm), suggesting the presence of pseudo-single domains, with multi-domain-like and single-domain-like of radius ~5nm. The temperature dependence of coercivity give us an estimated value of blocking temperature of ~ 402K. Possible uses of these material point to magnetic resonance imaging and other biomedical applications.