Microwave Magnetic And Microwave Absorption Properties Of The Easy-plane FeCoB Powders

Recently, with the development of electronic devices and communication technology, more and more attention has been focused on microwave magnetic materials. The frequency of electromagnetic wave has reached gigahertz range. The electromagnetic interference and electromagnetic pollution have drawn more attention as a kind of environmental pollution. To solve these problems, it is necessary to exploit a new type of microwave absorption materials with thinner thickness, lighter weight, wider frequency band of microwave loss and more intensity of microwave absorption. FeCoB is an excellent soft magnetic material with high permeability, proper permittivity, high saturation magnetization and low coercivity. According to the microwave absorbing theory, the easy-plane materials can exceed Snoek’s limit and obtain excellent high frequency magnetic properties. The flake and easy-plane FeCoB powder has been developed as a kind of excellent microwave absorbing materials.In this work, FeCoB powder was prepared using arc smelting, strip casting and ball milling method. The Fe particle with 99.99% purity, Co slice with 99.9% purity and FeB particle with 97.6% purity were used to smelt in the experiment. The samples were smelted in the melting furnace, and argon was used as the shielding gas. After arc melting, the samples were placed in a quartz tube. The quartz tube was placed into a quenching machine, and argon was used as the shielding gas. After rapid quenching, The samples were placed into a stainless steel for dry ball mill. After sieving process, the samples were prepared for wet ball mill. After ball milling, the samples were used to measure XRD, VSM, SEM and PNA. The details and results are listed as follows:1. The optimized condition of dry ball mill is:the ball milling pot is made of stainless steel tank; the volume of stainless steel tank is 100 milliliter; the ball milling time is 8 hours; the ball milling speed is 500 r/min; the method of ball milling is alternating ball milling. The optimized condition of wet ball mill is:the ball milling pot is made of stainless steel tank; the volume of stainless steel tank is 100 milliliter; the ball milling time is 8 hours; the ball milling speed is 500 r/min; the method of ball milling is alternating ball milling; the process control agent is isopropanol. To investigate the magnetic moment distribution of the easy-plane particle, the Mossbauer spectra was performed on the oriented sample. The orientation degree of magnetic moment is 86.47%. This result indicates that easy-plane particles were fabricated.2. To reduce the permittivity of the easy-plane FeCoB particles, the surface of FeCoB particles were coated with a thin layer of coupling agent. After coating coupling agent layer, the permittivity decreases significantly and better absorbing performance was obtained.3. In order to further enhance the high frequency properties, the FeCoB particles were oriented in an external magnetic field. After that, the permeability of the easy-plane FeCoB powder/paraffin composite is much larger than that of the original one, but the permittivity also shows an obvious increase. High permeability and proper permittivity is necessary for excellent microwave absorbing properties. As a result of the high permittivity, the microwave absorption properties of oriented FeCoB particles show no obviously increase.4. The relationship between complex permeability and complex permittivity at the perfect matching point is studied. The value of complex permittivity changes with the complex permeability at the perfect matching point is described by the contour map. According to the contour map, the complex permittivity at the perfect matching point can be estimated. Therefore, better microwave absorbing performance can be achieved by contour map.