Influence of thermal decomposition on morphologies and magnetic properties of iron nanofibres via electrospinning

Ferromagnetic iron nanofibres with diameters around 120 nm were prepared by electrospinning the polyvinyl pyrrolidone (PVP)/Fe(NO₃)₃ sol-gel solution and subsequent heat treatment. Two different heat treatments were carried out. One is heating the precursor nanofibres at 700-C for 2-h in hydrogen atmosphere directly (one-step way). The other heat treatment method is calcining the precursor nanofibres at 550-C for 1-h in air to form the ferric oxide, which was deoxidised at 700-C for 1-h in hydrogen atmosphere afterwards (two-step way). The thermal stability of PVP/Fe(NO₃)₃ composite nanofibres was investigated using thermal gravimetric techniques. The morphologies and structures of iron nanofibres were characterised by X-ray diffraction and the field emission scanning electron microscope, equipped with an energy-dispersive X-ray spectrometer. Magnetic hysteresis scans were performed by a vibrating sample magnetometer at room temperature. Compared with the sample prepared by two-step heat treatment, the iron nanofibres obtained from one-step way present better morphologies and magnetic properties, with saturation magnetisation and the coercivities were 207.4 Am² kg^-1 and 4.1 KA m^-1, respectively.