Microstructural investigation and magnetic properties of CoFe2O4nanowires synthesized inside carbon nanotubes

Abstract

Cobalt ferrite nanowires with an average diameter of 50 nm and lengths up to several micrometers were synthesized inside multi-walled carbon nanotubes under mild reaction conditions, i.e. 100 °C and atmospheric pressure, using an aqueous nitrate precursor salt filling the tubes. The concept of a confinement effect inside carbon nanotubes has been advanced to explain the formation of CoFe₂O₄ under such mild reaction conditions. The formation of caps near the tube tips at the beginning of the nitrate decomposition meant that each nanotube was considered as a closed nanoreactor, in which the reaction conditions could be very different to the macroscopic conditions outside the tube. A post-synthesis treatment under inert atmosphere allowed the growth of CoFe₂O₄ particles, from a disordered hair-like dendritic structure at 100 °C to highly crystallized domains at higher temperatures. A material with high coercivity at room temperature for small particles of about 25 nm in diameter was obtained by submitting the CoFe₂O₄ nanowires after calcination in air at 100 °C to an argon treatment at 550 °C for 2 h.