| With the rapid development of microwave technology, the high-frequency electronic devices and wireless communication in GHz frequency range have been widely applied in many fields. The corresponding electro-magnetic interference (EMI) problems become more and more serious, which precipitates the more requirements of the high-frequency magnetic materials and microwave absorption materials. FeCuNbSiB is a kind of preferable soft magnetic materials with high magnetization, low coercivity, and high static permeability. However, it is not wide to be studied and used in high-frequency for FeCuNbSiB.In this work, we prepared FeCuNbSiB planar anisotropy particles using ball milling method, and the high-frequency magnetic properties and microwave absorption properties of the FeCuNbSiB planar anisotropy particles were analyzed and optimized in theory and experiment, respectively. Finally, we obtained the materials with excellent high-frequency magnetic properties and microwave absorption properties. The details and results of our research are listed as below:1. In our experiment work, we break the FeCuNbSiB ribbons into micro-sized flake-shaped particles using a vibrating ball mill. The amorphous ribbons are firstly annealed in different temperature (450℃and 540℃). Then, the ribbons are milled in the same condition. The influence of crystallinity on the milled particles is obtained by measurement their properties. The FeCuNbSiB ribbons annealed at 540℃can be well crystallized and milled into micro-sized flake particles. For preparing flake particles with different size, the ribbons annealed at 540℃are first broken into chips and then milled with different times (2 h,4 h,6 h,8 h,10 h) using a ball mill. The 2 h-milled powder has higher saturation magnetization, lower coercivity, and higher permeability in high-frequency range. With the prolonging of the milling time, the saturation magnetization of the powder is reduced and the coercivity of the powder is increase, which is the result of introducing the impurities and stress in the milling process. By analyzing the Mossbauer spectra of oriented samples, the oriented angle of the samples is 64.6°, so the oriented degree is 90.2%, which indicates the particles have planar anisotropy.2. In order to further enhance the high-frequency magnetic properties and microwave absorption properties of the FeCuNbSiB planar anisotropy particles, we optimized the properties of the particles by the following methods:(1). Annealing treatmentFor enhancing the properties of the samples, the 2 h-milled powder is annealed to remove the stress introduced in the milling process. The time of annealing treatment is about 30 min under 300℃,400℃,500℃,600℃, and 700℃, respectively. For the particles/paraffin wax composites, the higher permeability is obtained by annealing at 300℃-500℃, which is the result of the better crystallinity and smaller stress after annealing. The annealing at 600℃and 700℃can make the FeB phase precipitated and degrade the performance of samples.(2). Rotational magnetic field orientationThe permeability of the oriented composite (35 vol%) increases markedly as an average factor of 1.2-1.3 compared with the unoriented one, while the resonance frequency has basically no change. By introducing theory model to calculate the permeability spectra and compare with the experimental results, the accordance results are obtained when the effective magnetic field He is chosen as 100 Oe and the damping coefficient a is chosen as 0.4. The value of (μi-1)fr exceed the Snoek's limit for the powder and its composites, which is because of bianisotropy and proves its effect for improving the high frequency magnetic properties. The particles/paraffin wax composites after rotational magnetic field orientation have larger permeability and smaller permittivity, which improves the impedance matching and enhances the properties of the microwave absorption. However, the high permittivity is still larger than the permeability, so the matching is not ideal.(3). Coating by oxidizationFor reducing the permittivity of the composites, it's feasible to employ a weak but moderate oxidization reaction occurring on the surface of flake particles. We added the as-milled powder into the mixture of hydrogen peroxide (30% solution) and anhydrous alcohol under an ultrasonic action for certain time. Then, the powder was naturally dried in room temperature. The oxidization conditions are chosen by altering the dosage of hydrogen peroxide, the power of ultrasonic, and the time of ultrasonic. The proper oxidization condition is obtained by comparing the reflection loss of the samples. The oxidized powder/paraffin wax composites have little different permeability and much smaller permittivity with the raw powder/paraffin wax composites, which realizes better matching of impedance and clearly enhances the properties of the microwave absorption.
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