Effects of γ-Fe₂O₃ on γ-Fe₂O₃/Fe₃O₄ composite magnetic fluid by low-temperature low-vacuum oxidation method

Highlights: • The different ratio of γ-Fe₂O₃ and Fe₃O₄ nanoparticles were prepared by LTLV oxidation method. • The γ-Fe₂O₃ nanoparticles can increase the dispersion and magnetization of γ-Fe₂O₃ and Fe₃O₄ composite magnetic fluid. • The LTLV oxidation method is low-cost and simple. In this paper, the controllable γ-Fe₂O₃/Fe₃O₄ composite nanoparticles were prepared by low-temperature low-vacuum oxidation of Fe₃O₄ directly in different time. The Fe₃O₄ nanoparticles were synthesized by chemical co-precipitation, and they were almost spherical particles and had no significant changes during the thermal oxidation. The prepared samples were identified by X-ray powder diffraction (XRD), Raman spectra (RS), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The γ-Fe₂O₃/Fe₃O₄ was obtained by Fe₃O₄ oxidized from 0 to 24 h, pure γ-Fe₂O₃ was obtained by Fe₃O₄ oxidized 24 h and its saturation magnetization was 55.86 emu/g. The magnetic nanoparticles were evenly dispersed in the silicone oil under the help of oleic acid and emulsifier, the Fe₃O₄, γ-Fe₂O₃/Fe₃O₄ and γ-Fe₂O₃ magnetic fluid with same viscosity were prepared. In the initial stage of thermal oxidation, the saturation magnetization of magnetic fluid increased with the oxidation time increasing, with the thermal oxidation going on, the saturation magnetization of γ-Fe₂O₃/Fe₃O₄ magnetic fluid kept growth until it reaches the maximum critical value and the corresponding oxidation time was 16 h, and then it began to decrease. And the maximum saturation magnetization of prepared γ-Fe₂O₃/Fe₃O₄ magnetic fluid was 25.08 emu/g, which was much higher than that of Fe₃O₄ magnetic fluid (12.45 emu/g) and γ-Fe₂O₃ magnetic fluid (14.25 emu/g).