The Magnetic Properties Of Fe₃O₄ Based Magnetic Nanocomposites

The magnetic nanocomposite materials has many unique features and excellent performance. Gradually, they are frequently used in our life and production, such as high-speed motor, magnetic levitation trains moving at a high speed, print motor, the disc motor, bicycles and motor vehicles, and so on. So our work efficiency, quality of life, energy consumption and other aspects have been improved to a considerable extent. Ferroferric oxide and cobalt ferrite are spinel ferrites and traditional magnetic materials, which have excellent performance and good chemical stability and smaller dielectric loss and so on. Compared with the alloy materials, the preparation cost is lower and the corrosion resistance is better. First, pure CoFe2O4, pure Fe3O4 and CoFe2O4/Fe3O4 nanocomposites with different concentrations of soft ferrite (Fe3O4) were fabricated using a co-precipitation method. Crystal structure, phase composition, morphology, magnetic properties and phase stability of as-synthesized pure CoFe2O4、 pure Fe3O4 and nanocomposites were characterized by X-ray diffraction (XRD), inductively coupled plasma (ICP), Mossbauer spectroscopy (MS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM), thermogravimetric analysis (TGA). Results from XRD and MS reveal that the nanocomposites are composed of two phases (CoFe2O4 and Fe3O4) and both of which have spinel structure and no disppearance of impurity phases. SEM and TEM show that all the CoFe2O4/Fe3O4 nanocomposites are composed of near-spherical nanoparticles. The average grain size is about 20 nm. VSM indicates that all hysteresis loops exhibit a single-phase-like behaviour. The remanence ratio (Mr/Ms), coercivity (HC) and maximum magnetic energy product (BH)max are significantly enhanced in all the nanocomposites compared with the pure hard ferrite (CoFe2O4). The enhancement of magnetic properties may be attributed to the exchange coupling interaction in the system. TGA results show that CoFe2O4/Fe3O4 nanocomposites have strong phase stability under high temperature. Then CoFe2O4/Fe3O4 nanocomposites was prepared by deposition method, and the structure, composition and magnetic properties of CoFe2O4/Fe3O4 were determined by MS, VSM and TGA. Results from MS reveal that no impurities in CoFe2O4/Fe3O4 nanocomposites are detected. VSM results show that the CoFe2O4/Fe3O4 magnetic properties prepared by deposition method are lower than that of CoFe2O4/Fe3O4 with co precipitation synthesis. The weakening of the magnetic properties may be due to the preparation method, which may lead to the failure of the exchange coupling. Moreover, it is found that the appropriate annealing temperature can enhance the magnetic properties of CoFe2O4/Fe3O4. This may be due to annealing enhances the soft magnetic phase (Fe3O4) and hard magnetic phase (CoFe2O4) between the exchange coupling effect in the CoFe2O4/Fe3O4 nanocomposites. TGA results show that the phase stability of CoFe2O4/Fe3O4 nanocomposite is good under high temperature.