Synthesis And Property Investigation Of Magnetic Composite Particles

In this paper,γ-Fe₂O₃ nanoparticles embedded in SiO₂ matrix and Bi substituted garnet (Bi-YIG) magnetic nanoparticles were prepared and the properties of the obtained nanocomposites were systematically studied.1. Using tetraethylorthosilicate and ferric salt as raw materials,γ-Fe₂O₃/SiO₂ nanocomposites were prepared through sol-gel method. The influence of ferric salts, solvents and acids on the crystalline structure and properties of the obtained nanocomposites were investigated. The particle sizes and properties ofγ-Fe₂O₃/SiO₂ nanocomposites were studied by Fourier Transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy and vibrating sample magnetometer. The results indicate that different ferric oxides are obtained using different ferric salts as precursor, and acids have a great important influence on the properties of the products. That is, hematite embedded in SiO₂ is obtained when hydrochloric acid is added. As nitric acid added during the preparation procedure,γ-Fe₂O₃ nanoparticles embedded in SiO₂ matrix are obtained. Compared with the particles prepared without acid, the obtained nanoparticles get bigger and also the saturation magnetization is enhanced as nitric acid added. As acetic acid replaced nitric acid added, the particle sizes of the formedγ-Fe₂O₃ which are uniformly dispersed in silica matrix decrease with a narrow particle size distribution, however, the saturation magnetization is reduced. The formation mechanism of theγ-Fe₂O₃ embedded in SiO₂ matrix is discussed.2. Maghemite nanoparticles homogeneously dispersed in silica matrix were obtained via a three-step chemical procedure at mild conditions. The acid treated solids were obtained using silica NPs, Fe(NO₃)₃·9H₂O and acetic acid through ball milling method followed by rapid removal of the solvent using a rotary evaporator. The nanocomposites were prepared by heating the acid-treated solids at 80℃for 2 h and then at 400℃for 1 h. The acid treated solids were studied by means of Fourier Transform infrared spectroscopy and thermogravimetry. The morphology and particle sizes of the magnetic nanoparticles were evaluated by the transmission electron microscopy technique, while the nature of the obtained nanocomposites were studied using X-ray powder diffraction and vibrating sample magnetometer. The results show that the acid treatment plays a critical role for the magnetic-phase formation, that is, hematite was obtained without acid treated while maghemite with narrow size distribution was obtained after acetic acid added. The maximum saturation magnetization ofγ-Fe₂O₃/SiO₂ nanocomposites with 44.5wt% maghemite was 37.78 emu·g^-1. Magnetic fluid was prepared using the obtainedγ-Fe₂O₃/SiO₂ nanocomposites by high-energy ball milling and was characterized by UV-vis, Gouy magnetic balance and rotating rheometer.3. Bismuth substituted yttrium iron garnet (Bi-YIG) nanoparticles were prepared by coprecipitation and subsequent heating treatment. Thermal gravity-differential thermal analysis was performed to investigate the thermal behaviors of the Bi-YIG precursors and to decide the best annealing temperature. Phase formation of garnet nanoparticles and particle sizes were investigated by X-ray powder diffraction and transmission electron microscopy, respectively. The magnetic properties were measured using vibrating sample magnetometer. The results show that the temperatures needed for the transformation of Bi-YIG from amorphous phase to garnet phase decreases with the increasing Bi content. The saturation magnetization of Bi-YIG nanoparticles increases as the Bi content increases. The Bi-YIG NPs with sizes of 28-78 nm were obtained after heating treatment at 650-1000℃. The Bi-YIG doped PMMA composites were prepared by in-situ bulk polymerization after MMA monomer mixed with Bi-YIG NPs. The results of Faraday rotation investigation of Bi-YIG/PMMA nanocomposites show that the angle of Faraday rotation increase with the Bi content and the figure of merit of the composites increases with the decreasing laser wavelength. The Bi-YIG NPs doped PMMA composites are new promising materials for magneto-optical devices.