| Recently, there has been great development in communication and information technology. There are more and more people who have paid attention to the microwave magnetic materials. In such microwave applications, the operating frequencies have reached the gigahertz region, and both high initial permeability and high resonance frequency are required. However, there exist a Snoek's limit for the conventional microwave magnetic materials, which means the product of permeability and resonance frequency is in proportion to the saturation magnetization. As a result, for conventional microwave materials, they always have a high resonance frequency while a low initial permeability. In the past several years, great effort has been made to exceed the Snoek's limit. According to the bianisotropy picture, high performance microwave magnetic materials can be obtained when the materials have an easy magnetic plane.Therefore, according to the bianisotropy picture, the aim of this work is to prepare high performance microwave magnetic materials. We focus on the FeCo film and FeCo powders, because they have easy plane and meet the demand of bianisotropy picture. Moreover, the FeCo alloy magnetic materials have high saturation magnetization, which is beneficial to achieve high permeability and high resonance frequency.Generally, the soft magnetic films are obtained through methods such as molecular beam epitaxy, thermal evaporation, sputtering, electrodeposition, electroless plating, and so on. Among them, electrodeposition technique is now emerging as an important method because of its low cost, high deposition rate and easy process control. In this work, we successfully prepared FeCo films and plate-like FeCo powders by electrodeposition. And then the structure, morphology and magnetic properties of the samples have been investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), Agilent E8363B vector network analyzer, inductively coupled plasma-atomic emission spectrometry (ICP) and Mossbauer spectroscopy.The main contents of this paper have been listed as below:(1) Fe-Co soft magnetic films with tunable high-frequency magnetic properties were successfully electrodeposited onto ITO conductive glass substrates using a conventional three-electrode cell. During deposition, an external magnetic field was applied in the FeCo film plane to induce an easy magnetic plane and an in-plane uniaxial anisotropy.(2) The influence of electrodeposition parameters on the structure, morphology and magnetic properties of FeCo films has been investigated. We focused on how the composition, film thickness and electrolyte temperature affect the in-plane, out-of-plane anisotropy field and microwave magnetic properties.(3) For electrodeposited FeCo films, well-defined uniaxial magnetic anisotropy could be induced only when the Fe content of deposit is between35and53at.%. At higher or lower Fe content, the anisotropy could not be induced in spite of the magnetic field applied during deposition. As film thickness increased, the surface roughness decreased. When the thicknesses are lower than540nm, the magnetization has a component out of film plane due to the rough surface. When the thicknesses are larger thant540nm, the films'surfaces become smooth and good microwave performances can be achieved. As the electrolyte temperature increased, both the in-plane and out-of-plane anisotropy fields increased, and as a result the resonance frequency increased also.(4) The optimized electrodeposition parameters have been obtained:the concentration of FeSO4·7H2O and CoSO4·7H2O are0.1M; the concentration of H3BO3is0.4M; electrolyte temperature:40℃; electrolyte pH:2.5; deposition potential:-1.6V; film thickness:1μm. For the optimized electrodeposited Fes2Co48film, the initial permeability is220and the resonance frequency is4.35GHz.(5) The optimized Fe52Co48film has been peeled off from ITO conductive glass substrate and then the plate-like FeCo powers were obtained. The composites were prepared by mixing the FeCo powers with paraffin wax or resin epoxy and their microwave magnetic properties, microwave absorption mechanism and properties were investigated.(6) For planar anisotropy FeCo composites, the permeability increased with increasing volume concentration and the (μi-1)-fr are larger than the Snoek's limit. The align process can improve the microwave magnetic properties. For different (oxidized by H2O2, aligned or mixed by resin epoxy) planar anisotropy FeCo (30vol.%) composites, when the thickness were above2mm, the minimum microwave absorption values can be smaller than-10dB. For the same volume concentration samples, as the thickness increased, the peak frequency decreased, which can be explained by the quarter-wavelength (A/4) matching model.
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