| With high-frequency and miniaturization trend of communication and computation devices, the electromagnetic interferences are the main hindrance to develop new devices working at higher frequency (> GHz). According to the ferromagnetic resonance, development of novel materials that can absorb high frequencies electromagnetic wave has attracted much attention during the past decades, since the tranditional absorbing materials with lower magnetic permeability and electrical resistivity could not meet work requirements at such high frequency. Therefore, development of novel materials, which can absorb electromagnetic wave at high frequency, is an urgent issue for the next genernation communication and computation technology.In the present thesis, submicron and micron-scale Fe-B-P particles with high saturation magnetization and low coercivity were prepared by chemical method, in order to solve the current problems of high frequency absorbing materials. A novel method was proposed to produce one-dimensional Fe-B-P chains in submicron scale, in which a magnetic field were employed to induce anisotropy growth of the Fe-B-P chains during the chemical preparation process. These Fe-B-P chains with high shape anisotropy can enhance the high magnetic permeability at high frequency. In addition, the produced Fe-B-P chains and NiZn ferrite nanoparitcles are integrated into anisotropic composites, which have excellent absorbing properties at high frequency band. And also, a kind of rod-shaped Bacillus was employed to prepare Fe-P micron rods. The microstructure and magnetic properties of these particles and composites were systematically investigated in the present study. There are some valuable results are following:Amorphous Fe-B-P submicron particles were succesfully produced by chemical reduction method. The influence of the pH value, the concentration of reductant, dropping speed, stirring speed, surfactants were systematically investigated. The optimized parameters to produce Fe-B-P paricles have been obtained:the pH value is 9, the reductant concentration is 2 g/25mL, the dropping speed of water is 200 mL/h, the stirring speed is 250 r/min, the molar ratio of FeCl2 and urea (nFe/nurea) is 1:1. The diameter of synthesized paritcles is about 0.2-0.3μm, Ms is 130 emu/g, and coercivity is 8 Oe. Annealing treatment under reasonable temperature (within 300℃) can keep amorphous state of the particles, and improve the inner stress and structure defect, and enhance the magnetic property. Amorphous Fe-Co-B-P submicron particles were produced by introducing CoCl2 reactant. With the increment of Co, the particle size decreases gradually. The shape of the particles transforms from sphere into cube.Fe-(NiZn)Fe2O4 composites and Fe-FeBP composite ribbons were fabricated by integrating the Fe-B-P submicron particles (-0.3μm), (NiZn)Fe2O4 nanoparticles (10 nm) and carbonyl Fe powder. Compared to the traditional Fe3O4 nanoparticles, (NiZn)Fe2O4 nanoparticles (69 emu/g) and Fe-B-P submicron particles (130 emu/g) perform a the higher Ms. The initial permeability of Fe-20 vol.%(NiZn)Fe2O4 composite is 33, the resonant frequency is about 1 GHz, whereas the resonant frequency of Fe-FeBP composite increased up to 2 GHz, and the Ms is 850 emu/cc.Amorphous Fe-B-P submicron chains were successfully prepared by introducing an external magnetic field in order to improve the shape anisotropy. The length of the chains can be tuned by changing the magnetic field. Fe-B-P chains-(NiZn)Fe2O4 composite ribbons have been prepared by using the Fe-B-P chains and (NiZn)Fe2O4. The composite ribbon prossesses a pretty high intrinsic permeability (150) when the content of (NiZn)Fe2O4 nanoparticles is 20 vol.%. The resonant frequency of Fe-B-P chains-20 vol.%(NiZn)Fe2O4 composite with thickness of 20μm is about 20 GHz, and the power loss is 70%, which is much higher than that of pure Fe-B-P chains. The increment of product of the resonant frequency and permeability shows the breakthrough of Snoek’s limit.Fe-P micron rods with Bacillus subtilis inside were synthesized by a novel biotemplating method. The influence of the PVP dosage, the pH value, the concentration of reactants and reductant, were systematically investigated and the optimized parameters to produce Fe-P rods were obtained. Fe-P micron rods-(NiZn)Fe2O4 nanoparticles composite ribbons have been fabricated. Intrinsic permeability of the composite ribbon fabricated by using long rods is 25, and the resonant frequency is high up to 7 GHz due to the large shape anisotropy. Ms of the composite fabricated by using Fe-P short rods reaches up to 400 emu/cc. The intrinsic permeability increased from 41 to 52 with addition of 20 vol.%(NiZn)Fe2O4 nanoparticles, and the resonant frequencies of Fe-P short-rod composites were about 5 GHz. The permeability and permittivity were almost the same in 1 GHz range, which means the composite has an impedance matching that can reduce reflection of the incident wave and enhance absorption performences. It’s expected that this material with high-frequecny absorption properties has a wide application prospect. |
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