Microwave Magnetic And Microwave Absorption Mechanism Of FeSiAl Planar Anisotropy Powders Composites

Recently, much effort has been devoted to microwave magnetic materials not only because of military purposes but also for the sake of solving the seriously electromagnetic interference due to the widespread application of information technology and wireless communications. With the applications of magnetic materials and magnetic devices in the field of higher working frequency, modern information technology, telecommunication and electromagnetic compatibility demand the ferromagnetic materials with even higher working frequency and higher magnetic permeability in the meantime. FeSiAl is a kind of preferable soft magnetic materials with high magnetization, low coercivity, high resistivity, and high static permeability. However, it is applied to high-frequency potential.In this work, we prepeared FeSiAl planar anisotropy powders using ball milling method, and the high-frequency magnetic properties and microwave absorption mechanism were analyzed. The details and results of our research are listed as below:1. In our experiment work, the experimental works are main contents of the vibration ball mill for preparing planar anisotropy FeSiAl powders. The FeSiAl powders having a larger diameter thickness ratio. Firstly, the preparations of the planar FeSiAl milling conditions were studied. Change of milling medium, milling time and other conditions for having the highest plane orientation FeSiAl powders. When using n-hexane as milling medium, changing the ball milling time the FeSiAl powders are irregular in shape and with increasing the milling time of particle size decreased. When using alcohol as milling medium, changing the ball milling time can be getting the flake FeSiAl powders. Because FeSiAl has excellent soft magnetic properties, its magntic anisotropy field is small, so the shape anisotropy of the influence that the flaky FeSiAl powders substantially along the inner distribution of magnetic moment. So can get the planar anisotropic FeSiAl powders. Through the Mossbauer spectral analysis, in alcohol4h milling samples have the best plane orientation, the sample orientation angle is69.6degrees, so the orientation reached93.7%, description of particles having the planar anisotropy. In order to further expand the sample frequency performance, the milled powders annealed. Annealing the FeSiAl there are two main aspects, eliminating the milling process is introduce in the stress influence; the FeSiAl powders with DO3superlattice structure is FeSiAl powders have more excellent soft magnetic properties. In alcohol milling4h samples were collected at500℃、600℃、700℃for1h under annealing. The sample after annealing initial permeability has been greatly improved, but the permeability decrease is faster. Also the plane type FeSiAl/paraffin composite made rotating magnetic field orientation processing, after rotating magnetic field oriented FeSiAl/paraffin composite material, its permeability has been greatly improved, and the resonance frequency of a certain reduction. For the35%volume fraction of particle composites, before orientation (μi’-1)fr=9.8GHz, after orientation (μi’-1)fr=12.2GHz, while2/3γ4πMs×Vc=6.5GHz. Visible, either before or after the orientation,values are exceeded the Snoek limit, this is because the planar anisotropy effect, but also proved for plane anisotropic model to improve the high frequency magnetic material has important significance.2. In plane orientation is the best FeSiAl powders, we will with different volume fraction of FeSiAl powders and paraffin is mixed to prepare composite samples of its microwave absorption properties. In the analysis of samples by microwave absorption properties of the process, we used a new characterization method. This method with the traditional characterization of microwave absorption materials performance compared to more comprehensive and scientific method. Volume fraction of15%,25%,35%FeSiAl/paraffin composite samples, will appear completely impedance matching. Total impedance matching point position with increasing sample concentration moves to low frequency. Volume fraction in a certain range, the reflection absorption peak position with the sample thickness increase moves to low frequency, and the absorption strength increases first then decreases.3. Using the prepared planar type FeSiAl powders, interfacial reflection model of reflection absorption mechanism is studied. Study finds reflection absorption peak position solely by the dielectric constant of the material, high frequency permeability and absorbing layer thickness is determined. Through the interface reflection model of electromagnetic energy flow are discussed, the energy of the electromagnetic wave in the material of the inner loss only a small part, most of the electromagnetic wave in electromagnetic wave absorbing materials surface interference cancellation.