Magnetic Properties Of Particles Synthesized By Chemical Method

With the rapid development of technology, the research work on materi-als has touched nano-scale. Owing to the distinct properties, Magnetic nano-scaled materials have an extensive prospect on biomedicine, magnetic fluid, electromagnetic wave absorption, magnetic recording, and so on. It is known that chemical method is the most effective way for the fabrication of mag-netic nanoparticles due to the simple device, low cost and the possibility of obtaining novel structure. Therefore, the chemical synthesis and investigation of magnetic nano-scaled materials are drawing more and more attention. In this work, monodisperse FeNi nanoparticles, dendritic CoNi microflowers and FeCo nanoplates were synthesized by chemical method and their magnetic properties were investigated as well. The main results are as follows:1. Synthesis of monodisperse FeNi nanoparticles by high temperature solution reduction method and investigation of their magnetic propertiesmonodisperse FeNi nanoparticles were synthesized by high tempera-ture solution reduction method. The size of particles could be tuned by changing the amount of surfactant TOP (trioctylphosphine) from 5-13 nm with the Ms variation from 20-40 emu/g.The content of Fe in FeNi nanoparticles is influenced by the type of reductant. There is much less Fe in the product than that in the original solvent when 1,2-Dodecanediol is used as reductant.A long time (more than 5 hours) of reaction lead to a large amount of oxidant and is not good to form FeNi particles.2. fabrication, investigation of magnetic properties and crystal structure of den-dritic CoNi microflowers Dendritic Co0.96Ni0.04 microflowers with the size of 5μm were fab-ricated by chemical reduction method using hydrazine as reductant. The microflowers were composed of dendritic "leaves" (2μm in length,500 nm in thickness). The XRD results revealed the coexistence of HCP and FCC phase. The Saturation magnetization (Ms) and coercivity (Hc) of as pre-pared flowers are 153 emu/g and 166 Oe respectively obtained form room temperature hysteresis loop.The crystallization are affected by the reaction temperature, a higher temperature benefits the crystallization and dendritic structure. Sixfold-symmetric snowflake were formed at the reaction temperature of 76℃.The Ni content of Co1-xNix plays a crucial role in morphology control. With the decrease of x from 0 to 0.5, the coexistence of HCP and FCC phase was replaced by pure fcc phase, accompanied by a transition from dendritic micro-flowers to aggregated spheric particles.The flower-like structure could be decomposed by the ultrasonic. Den-dritic "leaves" (2μm in length,500 nm in thickness) were obtained after a ultrasonic process. 3. Fabrication of FeCo nanoplates and the microwave absorption properties of FeCo nanoplates/paraffine wax compositesFeCo nanoplates (24 nm in thickness,100 nm in diameter) containing slight amount oxidation were synthesized at 66℃by chemical reduction method using hydrazine as reductant. The Saturation magnetization (Ms) and coercivity (Hc) of as prepared nanoplates are 143 emu/g and 76 Oe re-spectively. Additionally, the influence of reaction temperature on morphol-ogy were investigated. The mixture of micro-polyhedron and nanoplates were obtained at 76 and 86℃, while nanoplates seriously oxidized were obtain at 55℃.The microwave electromagnetic properties and microwave absorption properties of FeCo nanoplates/paraffine wax composites with the metalic volume fraction of 10 vol.%,35 vol.%,60 vol.%were investigated. The relative permittivity and permeability of the composites increase with the volume fraction increasing. Meanwhile, the dependence of microwave ab-sorption properties on volume fraction was also explored. For the composite with the volume fraction of 10 vol.%, a minimum reflection loss value of-4.6 dB was obtained at 11.1 GHz with the matching thickness of 4.0 mm. For the composite with the volume fraction of 35 vol.%, a minimum reflec-tion loss value of-35.0 dB was obtained at 13.4 GHz with the matching thickness of 1.5 mm, the bandwith of frequency corresponding to the re-flection loss less than-20 dB is 9.9-16.6 GHz with the matching thickness from 1.3-1.8 mm.For the composite with the volume fraction of 60 vol.%, a minimum reflection loss value of-35.4 dB was obtained at 8.8 GHz with the matching thickness of 1.5 mm, the bandwith of frequency correspond-ing to the reflection loss less than-20 dB is 6.3-9.9 GHz with the matching thickness from 1.4-2.0 mm.