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

In this paper, the controllable gamma-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 samplemagnetometer (VSM). The gamma-Fe2O3/Fe3O4 was obtained by Fe3O4 oxidized from 0 to 24 h, pure gamma-Fe2O3 was obtainedby 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, gamma-Fe2O3/Fe3O4 and gamma-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 gamma-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 gamma-Fe2O3/Fe3O4 magnetic fluid was 25.08 emu/g, which was much higher than that of Fe3O4 magnetic fluid (12.45 emu/g) and gamma-Fe2O3 magnetic fluid (14.25 emu/g). (C) 2016 Elsevier Ltd. All rights reserved.