【作者】 杨旭；

【导师】 李发伸；

【作者基本信息】 兰州大学 ， 凝聚态物理， 2012， 博士

【摘要】 近年来,随着现代通讯技术的发展,微波磁性材料的应用越来越广泛。在微波应用领域中,对微波磁性材料的磁导率和共振频率上的要求越来越高,人们希望在获得高的共振频率的同时获得高的磁导率。然而,传统的微波磁性材料中存在一个Snoek极限,即起始磁化率与共振频率的乘积和材料的饱和磁化强度成正比。由于Snoek极限的存在,对于饱和磁化强度一定的微波磁性材料,往往在获得了高的起始磁导率的同时其共振频率却很低；反之,获得了高的共振频率的同时其磁导率值却很低。为了突破Snoek极限,人们必须开发出新型的微波吸收材料。根据双各向异性模型,当磁性材料中存在一个易磁化面时,可以获得比传统磁性材料更为优越的微波磁性能,可以同时获得高的磁导率和高的共振频率。木文止是基于双各向异性模型,对平面磁各向异性型材料的微波磁性能进行了研究。我们选定的研究体系为平面磁各向异性型FeCo薄膜以及FeCo微粉复合材料。无论是薄膜还是微粉,都存在易磁化面,满足形成双各向异性的前提条件,并且FeCo合金具有高的饱和磁化强度。因此,该体系材料可以获得优异的微波磁性能。常用的制备薄膜的方法有很多,比如分子束外延、蒸镀,溅射,电化学沉积和化学镀等等。在众多薄膜制备的方法中,电沉积法的优势是工艺成本低,沉积速率快,适合大规模的工业化生产。在本文的工作中,我们采用电沉积法制备得到了具有易磁化面的FeCo薄膜和FeCo微粉材料,并利用X射线衍射（XRD）、扫描电子显微镜（SEM）、振动样品磁强计（VSM）、矢量网络分析仪（VNA）、原子吸收光谱和穆斯堡尔波谱等手段对样品的结构、形貌和磁性进行了研究,其中重点考察其微波电磁性能、微波吸收机理和微波吸收特性。本文的主要工作有以下几个方面：（1）利用恒电位电沉积模式,在ITO导电玻璃基底上成功制备出FeCo薄膜。通过在电沉积过程中外加磁场,使得FeCo薄膜具有平面各向异性,同时在面内诱导出了单轴各向异性。（2）系统地考察了电沉积工艺条件对FeCo薄膜结构、形貌和磁性能的影响,其中重点研究了薄膜成分、薄膜厚度、溶液温度等因素对FeCo薄膜面内、面外各向异性等效场和微波磁性的调控作用。（3）对于FeCO薄膜,只有当FeCO薄膜中Fe成分在35at.%和54at.%之间时,才能诱导出强的面内单轴各向异性,并同时获得优良的微波磁性。随着膜厚增大,FeCO薄膜表面粗糙度降低,当膜厚小于540nm时,较大的粗糙度导致磁矩在垂直于膜面方向有一个分量,影响了平面各向异性的形成；当膜厚大于540nm时,膜面粗糙度较小,平面各向异性较强,磁导率值较高。随着溶液温度升高,面内、外各向异性等效场均增大,导致其共振频率也随之增大。（4）通过系统地研究工艺参数对FeCO薄膜磁性能的影响,我们最终获得了微波磁性优良的FeCO薄膜的最佳制备工艺条件：镀液成分为FeSO₄’7H₂O0.1M； CoSO₄.7H₂O0.1M；H₃BO₃0.4M；抗坏血酸1g/L；溶液温度40℃；镀液pH值：2.5；沉积电位：-1.6V；膜厚：1μm。在最佳工艺条件下,可以制备得到具有优良高频磁性的Fe₅₂CO₄₈薄膜,起始磁导率为220,共振频率为4.35GHz。（5）通过将微波磁性能优异的平面型FeCO薄膜从基底上剥离下来,研磨后得到了平面磁各向异性型FeCO微粉,制备得到复合材料并考察其微波电磁性能、微波吸收机理及微波吸收特性。（6）对于片状FeCO微粉复合材料,随着FeCO微粉体积浓度的升高,介电常数和磁导率也随之增大。不同体积浓度的FeCo微粉复合材料的（μi一1）-f_r值均大于其相应的SnOek极限值；磁场旋转取向可以使得片状FeCo微粉/石蜡复合材料的微波磁性进一步提高；对于不同条件（双氧水氧化、磁场旋转取向、环氧粘接剂）的片状FeCO微粉复合材料（30vol.%）样品,当厚度在2mm以上时,均能实现-10dB以上的反射吸收；对于同一体积分数的复合材料样品,随着厚度增加,其反射损耗峰位将向低频移动,这一规律可以用四分之一波长关系予以解释。更多还原

【Abstract】 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.更多还原