The Structure And Magnetic Properties Investigation Of Rare-earth Ions Doped Ferromagnetic Nano-composites

The Fe/Fe3O4 composite has good mechanical properties and magnetic properties (relatively high saturation magnetization and low coercivity) and is an ideal ferromagnetic composite material. Meanwhile, Fe3O4 has a relatively low saturation magnetization, while the iron has a high saturation magnetization; so Fe/Fe3O4 composite can be synthesized in order to have more excellent magnetic properties. In this paper, we used the hydrothermal method and solvothermal methods by the disproportionation reaction of Fe2+ to synthesize Fe/Fe3O4 nanocomposites doping rare-earth ions, and study its magnetic properties systematically to find magnetic material with excellent magnetic properties.The products we synthesized are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Mossbauer spectroscopy (Mossbauer), vibrating sample magnetometer (VSM) and superconducting quantum interference device (SQUID).1. In the first chapter, we explained the status of nano-magnetic materials, introduced the magnetic properties of lanthanide ions and the research background of magnetic nano-materials doped with rare-earth ions, summarized and reviewed the synthesis of magnetic nano-rystalline doped with rare earth and the progress and problems of surface modification in recent years, and prospected the direction of the future research.2.We have adopted a series of hydrothermal methods to synthesize non-magnetic, as well as light and heavy rare-earth-doped (La3+, Sm3+, Gd3+, Nd3+) ions Fe/Fe3O4 Nanocomposites. We have studied the doped rare earth ions Fe/Fe3O4 system structure and magnetic properties. We synthesized a series of single-phase structure (i.e. with a body-centered cubic structure of the alloy, but also has face-centered cubic structure of magnetite) composite samples were studied and the effective ionic radius of rare earth ions on the sample structure and the magnetic moment can be studied. We found that measured at room temperature under the conditions of doped rare earth ions relative to the magnetic properties of the samples are not doped with a lowering in both samples. In accordance with the theory Nair, M=MB-MA, rare earth-doped (La3+, Sm3+, Nd3+) ions, rare earth ions are located in B replaced by Fe3+ ions bit, due to three kinds of rare earth ions are lower than the effective magnetic moment of Fe3+ in the effective ion magnetic moment, making B-site to reduce the effective ion magnetic moment, the last of the total magnetic moment of ions to reduce the sample to reduce the saturation magnetization. Gd3+ -doped samples to reduce the saturation magnetization, it is because:the one hand, the effective ion Gd3+ ion magnetic moment is 7.94μB, larger than the effective ion Fe3+ magnetic moment, Gd3+ ions are replaced by octahedral B-site lattice point Fe3+ ions, Fe3+ -Fe3+ interaction may be weaker than Gd3+ -Gd3+ interactions, but because of Gd3+ ions to replace the B-site small amount of Fe3+ ions is sufficient to sample the saturation magnetization. In addition, because the ionic radius of Gd3+ ions is larger than the ionic radius of Fe3+ ions, so to replace the Fe3+ ions Gd3+ ions, and not all of them into the magnetite spinel lattice to replace the B-site Fe3+, with the incorporation amount of Gd3-increases, making Fe3+ ion concentration and did not replace the samples the concentration of Fe3+ ions compared to a decrease, Fe3+ -Fe3+ interaction weakened, so saturation magnetization decreased.3. Through the solvothermal method, using the sodium oleate as a surface-active agent, we have synthesized monodisperse spherical nanocomposite with an average particle size of 230-270nm. Sodium oleate not only played a very good dispersion effect, but also had a protective effect on body-centered cubic structure of the alloy. Doped in rare-earth ions, the crystal structure of the samples did not change, but the grain size was larger than the non-doped sample, the reason was due to the radius of rare-earth ions doped Fe3+ greater than the particle radius (0.67A). The spherical nano-particles formation mechanism was explained by using Oster-Wald aging effects in detail. When doping in different rare-earth ions, the magnetic properties of samples changed a lot. With the increasing of rare earth, its saturation magnetization reduced; at the same time, the samples'coercivity increased This can be explained through interaction of the crystal structure and magnetic structure4. On the basis of the above work, we have synthesized bifunctional Fe/Fe3O4＠Y2O3:Eu3% composite with magnetism and luminescence, and discussed the interaction of magnetism and luminescence. The results showed that under UV irradiation, the luminescence intensity of Y2O3:Eu3%, YVO4:Eu3%, YPO4:Eu and YBO3:Eu increased, and with the extension of UV irradiation, the luminescence intensity increased. Under the influence of the magnetic field effects and UV irradiation, the luminescence of Y2O3:Eu3% enhanced. The influence of the magnetic field effects for the luminescence intensity is larger than that of UV radiation, which may be caused by d-f layer electrons of Eu3+ ion arranged differently under different conditions. The luminescence intensity of Fe/Fe3O4＠Y2O3:Eu3% nanocomposite under UV irradiation was stronger than that of the magnetic field effect. The saturation magnetization of Fe/Fe3O4＠Y2O3:Eu3% nanocomposites reduced under UV irradiation.