In this study, magnetite (Fe 3 O 4 ) nanoparticles with a size range of 8-20 nm were prepared by the modified controlled chemical coprecipitation method from the solution of ferrous/ferric mixed salt-solution in alkaline medium. In the process, two kinds of surfactant (sodium oleate and polyethylene glycol) were studied; then, sodium oleate was chosen as the apt surfactant to attain ultrafine, nearly spherical and well-dispersed (water-base) Fe 3 O 4 nanoparticles, which had well magnetic properties. The size and size distribution of nanoparticles were determined by particle size analyzer. And the magnetite nanoparticles was characterized by X-ray powder diffraction (XRD) analysis, transmission electron microscopy (TEM), electron diffraction (ED) photography, Fourier transform infrared spectrometer (FT-IR), and vibrating-sample magnetometer (VSM). Also the effect of many parameters on the Fe 3 O 4 nanoparticles was studied, such as reaction temperature, pH of the solution, stirring rate and concentration of sodium oleate. And the 5-dimethylthiazol-2-yl-2,5-diphenyltetrazolium bromide (MTT) assay was performed to evaluate the biocompatibility of magnetite nanoparticles. The results showed that the Fe 3 O 4 nanoparticles coated by sodium oleate had a better biocompatibility, better magnetic properties, easier washing, lower cost, and better dispersion than the magnetite nanoparticles coated by PEG.

We synthesized Fe3O4 microspheres using a solvothermal method and characterized their morphologies, structures, surface property and magnetism by field emission scanning electron microscopy (FE-SEM), powder X-ray diffraction (XRD) patterns, Fourier transform infrared (FTIR) absorption spectra, and vibrating sample magnetometer (VSM). The results showed that the synthesized Fe3O4 microspheres with a tunable size range of ca. 80–200 nm are composed of many Fe3O4 collective nanoparticles. XRD pattern confirmed that the Fe3O4 microspheres belong to cubic structure. Magnetic investigation reveals that the Fe3O4 microspheres have higher saturation magnetization and negligible coercivity at room temperature.