Synthesis and magnetic properties of nanocomposite Ni1−xCoxFe2O4–BaTiO3 fibers by organic gel-thermal decomposition process

Nanocomposites of ferrite and ferroelectric phases are attractive functional ceramic materials. In this work, the nanocomposite Ni1−xCoxFe2O4–BaTiO3(x = 0.2, 0.3, 0.4, 0.5) fibers with fine diameters of 3 ~ 7 μm and high aspect ratios were synthesized by the organic gel-thermal decomposition process from the raw materials of citric acid and metal salts. The structure, thermal decomposition process and morphologies of the gel precursors and the resultant fibers derived from thermal decomposition of the gel precursors were characterized by Fourier transform infrared spectroscopy, thermogravimetric differential thermal analysis, X-ray diffraction and scanning electron microscopy. The magnetic properties of the nanocomposite fibers were measured by vibrating sample magnetometer. The nanocomposite fibers of ferrite Ni1−xCoxFe2O4 and perovskite BaTiO3 are formed at the calcination temperature of 900 °C for 2 h. The average grain sizes of Ni1−xCoxFe2O4 and BaTiO3 in the nanocomposite fibers increase from about 15 nm to approximately 67 nm with the increasing calcination temperatures from 900 to 1,180 °C. The saturation magnetization of the nanocomposite Ni1−xCoxFe2O4–BaTiO3(x = 0.2, 0.3, 0.4, 0.5) fibers increases with the increase of grain sizes of Ni1−xCoxFe2O4 and Co content, while the coercivity reaches a maximum value at the single-domain size of about 65 nm of Ni0.5Co0.5Fe2O4 obtained at the calcination temperature of 1,100 °C.