| Due to their special physical and chemical properties, nano-sized magnetic particles put up different physical and chemical characteristics compared with general materials. Fe3O4 nanostructure has many unique properties and in magnetic recording, magnetic fluids, catalysis and other fields has potential applications. It`s has attracted much attention in the materials science. Recently, although there are a variety of preparations techniques are reported and adopted, however, the morphology control and the growth mechanism of nano-materials still need to further study. Compared with many chemical methods, we used hydrothermal and solvothermal to prepare Fe3O4 nanocrystal, nanowires, and flower-like nanostructures. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and superconducting quantum interference device (SQUID) were used to analyze the sample`s structure, morphology and magnetic properties. On this basis, Fe3O4 was coated on the carbon nanotubes. We discussed their absorbing wave properties. This paper includes the following components:1. Fe(CO)5 was used as the precursor. Fe3O4 nanocrystal was synthesized in appropriate reaction temperature and time by hydrothermal. XRD, SEM and SQUID were used to characterize the samples. It was found that reaction temperature, reaction time and stirring speed play important roles in the formation of the final Fe3O4 nanocrystal. Effect of reaction conditions on the phase and morphology were studied, possible growth mechanism and magnetic properties of the Fe3O4 nanocrystal was discussed.2. Fe(CO)5 was used as the precursor. Flower-like nanostructures Fe3O4 were synthesized in appropriate reaction temperature and time by solvothermal. XRD, SEM and SQUID were used to characterize the samples. It was found that reaction time was the key to control the morphology. Possible growth mechanism of the 3D flower-like structure Fe3O4 was discussed. We used ethanol and distilled water as solvents. Fe3O4 nanowires were synthesized by solvothermal method. We discussed the growth mechanism and magnetic properties of the samples.3. Fe(CO)5 was used as the precursor, The samples were successfully synthesized by carbon nanotubes coated with Fe3O4. With the increase of compound time, namely the increase of Fe3O4 layer thickness, the sample reflection loss significantly increasing, absorption bandwidth broadening, the corresponding reflection loss maximum points shift to the low frequency by the absorbing wave test utilizing microwave vector network analyzer. Compound can serve as a new type of electromagnetic "stealth" material because of its excellent absorbing wave properties.
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