| During the last decade a lot of research has been carried out to develop magnetic thin films for the use in high frequency devices. The basic demands for soft magnetic films operated in the gigahertz frequency range include high permeability, high saturation magnetization and appropriate in-plane magnetic anisotropy field so as to improve ferromagnetic resonance frequency (which determines the cut-off frequency for high frequency application). FeCo-based alloy soft magnetic thin films are one of candidates for realizing this purpose. These films possess the advantages of high permeability (low coercivity) of magnetic metal alloy, high saturation magnetization (24kG at Fe65Co35) and high ferromagnetic resonance frequency (high in-plane magnetic anisotropy). Consequently, the FeCo-based alloy soft magnetic thin films are applied in electromagnetic devices as high frequency components, such as magnetic recording head, micro-inductive devices and thin film transformers.In general, the film growth processes, such as sputtering and molecular beam epitaxy (MBE), require high or ultrahigh vacuum. Electrodeposition offers significant cost, reliability and environmental advantages over the previously used evaporation technology. And it is an established industrial process for producing films of magnetically-soft metals and alloys. In this work, FeCo and FeCoZr alloy soft magnetic thin films were prepared by electrochemical deposition. The FeCo and FeCoZr films were prepared by controlling technological parameters, such as solution concentration and temperature, additives, deposition potential. The microstructure, magnetic and electric properties, high frequency characteristics were investigated systematically by X-ray diffraction (XRD), scanning electron microscope (SEM). vibrating sample magnetometer (VSM). shorted microstrip transmission-line perturbation method, laser direct writing instrument and electron spin resonance spectrum instrument (ESR). The main researches were carried out as follows:Ⅰ. We have successfully prepared FeCoZr films onto ITO conductive glass substrates by electrodeposition, and the film with amorphous structure was obtained at-1.8V, which lead to films with low coercivity and higher in-plane anisotropy. The easy axis coercivity and hard axis coercivity decreased from30Oe to15Oe and from5.5Oe to3Oe, respectively. Furthermore, the magnetic anisotropy field increased to64Oe. The ferromagnetic resonance frequency was as high as3.4GHz, implying that the film is promising for high-frequency applications.Ⅱ. A simple laser etching method is utilized to adjust magnetic anisotropy and resonance frequency of patterned FeCo thin films from12to700Oe and from1.0to8.2GHz, respectively. The results show the demagnetization effect is yet evident when the strip widths vary from0.05mm to1.00mm. The magnetic anisotropy in the sample can be controlled by altering strip width and orientation under the action of induced magnetic field. The resonance frequency of unpattemed films is3.6GHz. When strip orientation is parallel to induced magnetic field direction, the resonance frequency of patterned films shifts to larger value with decreasing strip width. On the contrary, the resonance frequency decreases when strip orientation is perpendicular to induced magnetic field direction. In summary, the magnetic anisotropy and resonance frequency of the patterned thin films can be conveniently adjusted from12to700Oe and from1.0to8.2GHz, respectively. A shape anisotropy model based on the shape demagnetization effect is developed to estimate the effective in-plane uniaxial magnetic anisotropy. Using this model, the magnetic anisotropy field and resonance frequency may be calculated for strip patterned films, which can further promote the application of magnetic films in the high frequency.Ⅲ. The FeCo thin films are deposited on the curving substrates by electrochemical deposition to adjust the stress-induced magnetic anisotropy. The compressive stress is produced in the as-deposited films after the substrates are flattened. As a result, the magnetic anisotropy increases from105Oe to170Oe with the change of curvature of the flexible Cu substrate, and the resonance frequency can reach to4.8GHz. The intrinsic Hk and4πMs of the samples are obtained by FMR measurement. The hysteresis loops, anisotropies and high frequency properties have given a self-consistent evidence of the stress-induced anisotropy. The results show that the stress-induced magnetic anisotropy and the resonance frequency increase with the increasing of substrate curvature. The induced easy axis is perpendicular to the compressive stress direction. According the experimental results, a feasible method can be used to control the magnetic anisotropy of films.IV. The soft magnetic films with in-plane uniaxial magnetic anisotropy (IPUMA) were investigated by ferromagnetic resonance method. According to theory of FMR, theoretical model applied to films with IPUMA was developed to measure the intrinsic magnetic anisotropy field and saturation magnetization. It provided a method to measures magnetic parameters. |
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