Nanostructures and magnetic properties of cobalt ferrite (CoFe2O4) fabricated by electrospinning

This paper describes the fabrication of cobalt ferrite (CoFe2O4) nanostructures (in the form of nanofibers and nanoparticles) by the electrospinning method using a solution that contained poly(vinyl pyrrolidone) (PVP) and cheap Co and Fe nitrates as metal sources. The as-spun and calcined CoFe2O4/PVP composite samples were characterized by TG-DTA, X-ray diffraction, FT-IR, SEM and TEM, respectively. After calcination of the as-spun CoFe2O4/PVP composite nanofibers (fiber size of 320 +/- 48 nm in diameter) at 500, 600, and 800A degrees C in air for 3 h with different heating rates of 5 or 20A degrees C/min, either NiFe2O4 nanofibers of similar to 10-200 nm in diameter or nanoparticles with particle sizes of similar to 50-400 nm having a well-developed spinel structure were successfully obtained. The crystal structure and morphology of the nanofibers were influenced by the calcination temperature and heating rate. A faster heating rate allowed for a rapid removal of the PVP matrix and resulted in a complete change from fibrous structure to particle in the calcined CoFe2O4/PVP composite nanofibers. Room temperature magnetization results showed a ferromagnetic behavior of the calcined CoFe2O4/PVP composite nanofibers, having their hysteresis loops in the field range of +/- 4500 and 3000 Oe for the samples calcined respectively with heating rates of 5 and 20A degrees C/min. The values of the specific magnetization (M (s)) at 10 kOe, remnant magnetization (M (r)), M (r)/M (s) ratio, and coercive forces (H (c)) are obtained from hysteresis loops. It was found that the values of M (s), M (r), M (r)/M (s), and H (c) depended strongly on morphology of the CoFe2O4 nanostructures.