La/zinc/mnzn Doped Barium Z Hexagonal Microwave Absorbing Properties Of Cobalt Ferrite

The hexagonal ferrites with magnetoplumbite type strcture have an excellent microwave absorption property in the range of GHz frequency, but the modification of the ferrites by doping and other method to improved further their microwave absorption properties have been a hot and active topic. In this thesis, the microwave absorption properties of doping Z-type barium cobalt ferrites with hexagonal flake morphology were researched, which were doped by La at Ba site and Zn, MnZn at Co site, respectively.The crystalline powder samples of Ba3-xLaxCo2Fe24O41, Ba3ZnxCo2-xFe24O41and Ba3(MnZn)xCo2(1-x)Fe24O41were prepared by sol-gel method. The formation, crystal structure, particle morphology and element content of these samples were characterized by TGA-DSC, FT-IR, XRD, SEM, and EDS. The hysteresis loops of the samples were measured by vibrating sample magnetometer(VSM). The results showed that the formation of samples went through several stages (such as water evaporation, thermal decomposition and crystalline growth), the samples calcined above1250℃for5hours were single Z phase ferrites and their particle morphology was micro-hexagonal flake shape, and they had normal chemical ingredients and good soft magnetic properties.Their complex permittivity and complex permeability were measured by microwave vector network analyzer in the frequency range of2-18GHz, and the reflection coefficient and loss tangent were calculated according to measurements. The effects of doping content and thickness on microwave absorption of them and the microwave loss mechanism were discussed. The results showed that the absorption peak of Ba3-xLaxCo2Fe24O41(x=0.3) with2.10mm thickness was16.5,43.2dB at12.00,17.05GHz respectively and its bandwidth above lOdB was4.2GHz, the peak of Ba3ZnxCo2-xFe24O41(x=0.4) with2.10mm thickness was49.6dB at5.05GHz and the bandwidth was6.0GHz, and the peak of Ba3(MnZn)xCo2(1-x)Fe24O41(x=0.4) with2.20mm thickness was38.5dB at3.90GHz and the bandwidth was3.8GHz. The microwave absorption of them was resulted from both dielectric loss and magnetic loss. The magnetic loss of Ba3-xLaxCo2Fe24O41was main in the range of low frequency but its dielectric loss main in high frequency. The magnetic losses of Ba3ZnxCo2-xFe24O41and Ba3(MnZn)xCo2(1-x)Fe24O41were main but their dielectric losses weaker in the frequency range of2-18GHz. The micro-hexagonal flaky shape of the materials was helpful to microwave absorption of them.