Synthesis and microwave absorption properties of magnetite nanoparticles.
Synthesis and microwave absorption properties of magnetite nanoparticles.
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DOI：
10.1166/jnn.2012.4275
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发表时间：
2012-02
影响因子：
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通讯作者：
X. Shao;B. Dai;Xiaowei Zhang;Yongjun Ma
中科院分区：
文献类型：
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作者：
X. Shao;B. Dai;Xiaowei Zhang;Yongjun Ma
以FeCl3x6H2O、FeCl2x4H2O和NaOH为原料，采用共沉淀法合成了不同尺寸的Fe3O4纳米粒子。用X射线衍射仪、透射电子显微镜和振动样品磁强计对产物的晶体结构、形貌、粒径和磁性能进行了表征。结果表明，铁与铁的摩尔比对纳米Fe3O4的形成有重要影响。随着摩尔比从1：2到6：1，颗粒的平均直径从约10 nm膨胀到约20 nm，饱和磁化强度和矫顽力相应增加。用向量网络分析方法测量了Fe3O4与石蜡混合物的复介电常数epsilon(R)和磁导率µ(R)。基于金属板支撑的微波吸收层模型，用epsilon(R)和u(R)值确定了不同样品厚度下的反射损耗。随着厚度的增加，最小反射损耗或倾角向低频区移动。当厚度为5 mm时，摩尔比为6：1的Fe3O4和石蜡复合材料的最小反射损耗分别在5.2 GHz和17.6 GHz处分别达到-35.1和-30.2 dB。最小的反射损耗归因于吸收体的厚度接近传播波长的四分之一的奇数倍。
Nanoparticles of Fe3O4 with various sizes were synthesized from FeCl3 x 6H2O, FeCl2 x 4H2O and NaOH by coprecipitation process. The crystal structure, morphology, particle size and magnetic property of the products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). It was found that the molar ratio of ferrous to ferric played an important role in the formation of Fe3O4 nanoparticles. The particle mean diameter swelled from approximately 10 to approximately 20 nm with the molar ratio range from 1:2 to 6:1. The saturation magnetization and the coercivity increased correspondingly. The complex permittivity epsilon(r) and permeability mu(r) of the Fe3O4 mixture with paraffin were measured using vector network analysis. Values of epsilon(r), and mu(r) were used to determine the reflection loss at various sample thicknesses, based on a model of microwave absorbing layer backed by a metal plate. The minimal reflection loss or the dip shifts to a lower frequency region with increasing thickness. When the thickness is 5 mm, the minimal reflection loss of Fe3O4 synthesized with the molar ratio of 6:1 and paraffin wax composites reaches -35.1 dB at 5.2 GHz and -30.2 dB at 17.6 GHz, respectively. The minimal reflection loss is attributed to the thickness of the absorber approximates an odd number multiple of a quarter of the propagation wavelength.