Fabrication and magnetic properties of NiFe2O4 nanofibers obtained by electrospinning

Abstract NiFe2O4 nanofibers fabricated by electrospinning technique were investigated. The as-spun nanofibers were calcined at 400, 500, 600, 700 and 800 °C for 3 h with a heating rate of 1 °C/min. All samples were investigated by thermogravimetric-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and vibrating sample magnetometer (VSM). The XRD results indicate that all calcined samples present a pure phase with cubic spinel structure. The SEM images show that the average diameters of the nanofibers decrease from 82±16 to 64±18 nm with increasing calcination temperature, corresponding to the TEM results. FT-IR spectra of all samples with absorption band at 596 cm−1 indicate that there exists the stretching mode of the metal ion-oxygen of the spinel lattice. XANES spectra reveal the existence of Ni2+ and Fe3+ ions in the samples. The simulation XANES and EXAFS spectra of Ni and Fe ions show that Ni ions could occupy the octahedral site and Fe ions could occupy both tetrahedral and octahedral sites of the inverse spinel structure. VSM measurements show the soft ferromagnetism with a maximum magnetization of 40 emu/g for the sample calcined at 800 °C. The origin of ferromagnetism in the NiFe2O4 samples is discussed.