Fabrication and magnetic properties of Ni_0.5Zn_0.5Fe₂O₄ nanofibres by electrospinning

NiZn ferrite/polyvinylpyrrolidone composite fibres were prepared by sol–gel assisted electrospinning. Ni_0.5Zn_0.5Fe₂O₄ nanofibres with a pure cubic spinel structure were obtained subsequently by calcination of the composite fibres at high temperatures. This paper investigates the thermal decomposition process, structures and morphologies of the electrospun composite fibres and the calcined Ni_0.5Zn_0.5Fe₂O₄ nanofibres at different temperatures by thermo-gravimetric and differential thermal analysis, x-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscopy. The magnetic behaviour of the resultant nanofibres was studied by a vibrating sample magnetometer. It is found that the grain sizes of the nanofibres increase significantly and the nanofibre morphology gradually transforms from a porous structure to a necklace-like nanostructure with the increase of calcination temperature. The Ni_0.5Zn_0.5Fe₂O₄ nanofibres obtained at 1000 °C for 2 h are characterized by a necklace-like morphology and diameters of 100–200 nm. The saturation magnetization of the random Ni_0.5Zn_0.5Fe₂O₄ nanofibres increases from 46.5 to 90.2 emu/g when the calcination temperature increases from 450 to 1000 °C. The coercivity reaches a maximum value of 11.0 kA/m at a calcination temperature of 600 °C. Due to the shape anisotropy, the aligned Ni_0.5Zn_0.5Fe₂O₄ nanofibres exhibit an obvious magnetic anisotropy and the ease magnetizing direction is parallel to the nanofibre axis.