Study Of Synthesis And Magnetic Properties Of The γ-Fe₂O₃/CoFe₂O₄ Composite Nanoparticle And Ferrofluids

During the synthesis of the γ-Fe2O3 nanoparticles by chemical induced transition, Co(NO3)2 or Co(NO3)2/NaOH solution was added for surface Co-modification. Using vibrating sample magnetometer (VSM), X-ray diffraction (XRD), transmission electron microscope (TEM), high resolution transmission electron microscope (HTEM), X-ray dispersive spectroscopy (EDX) and X-ray photoelectron spectrometer (XPS), the specific magnetization, morphology, crystal structure, and bulk and surface chemical compositions have been characterized. The experimental results show that particles of no Co-modification are composed of γ-Fe2O3 core and CoCl2·6H2O shell, particles of only adding Co(N03)2 for modification are composed of γ-Fe2O3 core and CoG2·6H2O shell, particles of adding Co(NO3)2/NaOH solution for modification are composed of γ-Fe2O3 core with CoFe2O4 epitaxial layers and a CoCl2·6H2O outermost layer.CoFe2O4 and γ-Fe2O3 have similar spinel structures and lattice constants so that they could not be distinguished by XRD or TEM techniques. XPS can be used to distinguish them. The molar, mass, and volume percentages of each phase have been estimated for each sample by the measurements of EDX and XPS. and the average density and saturation magnetization are derived. The magnetization and coercivity of particles depend on the grain size of the spinel structure crystallites, but the anisotropy constant remains at 1.48×10-1 J/cm3.γ-Fe2O3 magnetic nanoparticles were prepared by the co-precipitation-chemically induced phase transition method. And polyvinyl alcohol (PVA) based γ-Fe2O3 ionic ferrofluids were synthesized using Massart method, in which volume fractions of PVA were from 0 to 1%. The magnetization behaviors of both the particles and ferrofluids have been measured by vibrating sample magnetometer (VSM). The experimental results show that while the volume fraction of particles is same, the ferrofluids which carrier liquid has PVA, whose reduced saturation magnetization will decreases with the increasing of PVA content in the carrier liquid. The saturation magnetization of ferrofluids containing PVA is less of the pure water-based ferrofluids, and the phenomenon is more obvious with the increasing volume fraction of PVA content in the carrier liquid. The reason may be that the preparation of γ-Fe2O3 nanoparticles form the ring pre-aggregate of magnetic flux closed in the PVA based ferrofluids, with the increase of PVA content in the carrier liquid, viscosity increase, the more difficult to spread of particles, the number of the ring pre-aggregate particles increase and the saturation magnetization decreases accordingly.Using the forming method to synthetic the γ-Fe2O3/CoFe2O4 ionic ferrofluids. The experimental results show that the composite nanoparticles is suitable for synthesis of ferrofluids. As the particle surface with acid corrosion layer, the reduced saturation magnetization of pure water based ferrofluids is approximately equally with the saturation magnetization of the particles. The experimental show that, the magnetic density and liquid viscosity will increase with the increase of glycerol volume fraction, but the saturation magnetization of ferrofluids decreases with the increase of glycerol volume fraction. The reason may be that the effection of nanoparticles form the ring pre-aggregate in the ferrofluids. With the same carrier liquid, The reduced saturation magnetization of y-Fe203/CoFe204 based ferrofluids is larger than the γ-Fe2O3 based ferrofluids, But the reduced initial magnetic susceptibility of γ-Fe2O3/CoFe2O4 based ferrofluids is less than the γ-Fe2O3 based ferrofluids.