The Ni_0.3Cu_0.2Zn_0.5Fe₂O₄ nanofibers with diameters of around 100 nm were successfully fabricated by sol-gel method combined with electrospinning technology. The as-spun polymer/inorganic composite nanofibers and calcined products were characterized by means of thermogravimetric and differential thermal analysis (TG-DTA), X-ray powder diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The experimental results showed that the pure spinel structure was basically formed when the composite nanofibers were calcined at 450 ℃ for 2 h. With the increase of calcination temperature, the nanofiber surface became much rougher and the nanofiber morphology gradually changed toward the necklace-like structure along with the growth of Ni_0.3Cu_0.2Zn_0.5Fe₂O₄ grains contained in the nanofibers. At the same time, the specific saturation magnetization (M_s) of nanofibers monotonously increased, while the coercivity (H_c) initially increased, reached a maximum value at about 650 ℃, and then decreased with further increasing calcination temperature, indicating that the single-domain critical size of Ni_0.3Cu_0.2- Zn_0.5Fe₂O₄ in the form of nanofibers may be around 53 nm. Furthermore, the relationship between the coercivity of Ni_0.3Cu_0.2Zn_0.5Fe₂O₄ nanofibers and the mean grain size (D) was analyzed in a D range below the single-domain critical size. It was found that H_c of these nanofibers varied as D^0.71, which was in good agreement with the predicted D^2/3 dependence of H_c on the basis of the random anisotropy model.

Key words: NiCuZn ferrite, nanofiber, electrospinning, magnetic property, calcination temperature