Preparation And Magnetic Properties Of Fe/N And Fe/C Composite Materials

As is regard as as the fourth-largest category material along with metal material, inorganic non-metallic material and polymer material, composite material is drawing increasing attention. And its development is greatly enriching the modern family of materials and improving their properties. Take for instance the magnetic materials, both traditional metal magnetic material and ferrite material have some limitations in application. Metal magnetic material shows higher saturation magnetization and low resistivity while ferrite material with lower saturation magnetization and high resistivity. The composite material is expected to complement each other’s advantages and provide a better way to get materials with better performance. We found that a lot of work had been done on the metal-oxide composites, but there is few reports on magnetic metal-nitrides composite materials. Compared with iron oxides, iron nitrides have higher saturation magnetization and stronger corrosion resistance, which the former does not posses. In this thesis, in order to achieve the preparation of Fe/N and Fe/C magnetic composite material, we explored the possibility of using ion implantation method which had been widely used in semiconductor processing to get composite materials. We also tried to find a new method get Fe/C magnetic nanoparticles with core-shell structure, and did characterization and magnetic study for the magnetic composite materials under different experiment parameters. The main contents and results are as follows:(1) The implantation of nitrogen ion into Fe film prepared through electrodeposition method get the surface nitrided, a magnetic composite film with y’-Fe4N as upper layer and Fe as under layer is formed. Different dose of implantation leads to different saturation magnetization and coercivity values. For the Fe films that was electrodeposited with magnetic fields superimposed during deposition, after nitrogen ion implantation it is found that ε-Fe3N and y’-Fe4N phases emerge simultaneously. With the increase of the implantation dose, the remanence ratio increases and the coercivity firstly decreases and then increases. In addition, the resonance peak would be effected by the proportion of y’-Fe4N and ε-Fe3N phase which emerged after different nitrogen ion implatation. (2) The implantation of nitrogen ion into electro-deposited FeNi film leads to the formation of γ’-Fe2Ni2N phase in the composite film. There are no new phases emerged for magnetron sputtering deposited FeCo film and electroless plated Ni-Co-P film after nitrogen ion implantation, while the sputtering effect is obvious during the implanting process. The phenomenon that the coercivity of FeCo films firstly decreases and then increases with increasing the nitrogen ion implantation dose could be explained by the change of surface morphology caused by implantation process and pinning effect caused by the accumulation of defect during implanting.(3) A two-step procedure method of hydrothermal and subsequent thermal reduction process is proposed synthesize carbon-encapsulated Fe nanoparticles. These ferromagnetic particles present a quasi-spherical shaped, core-shell structure with diameter ranged from10to20nm and a carbon shell of about4nm. After acid treatment for24h in4M HCl, it is found that the saturation magnetization of the nanoparticles decreases quite a lot, which means metallic nanoparticles that are non-encapsulated or encapsulated in defective carbon coating account for a large proportion.