Microwave Absorbing Properties Of Z-type Strontium Cobalt Hexaferrite Doped By Ce/NiZn And Compounded By La_0.7Sr_0.3MnO₃

The modification of the ferrites by a variety of methods such as ion doping, compounding etc, have been a hot and active topic to improve further their microwave absorption properties. In this thesis, the microwave absorption properties of Z-type strontium cobalt ferrites were researched, which were doped by Ce at Sr site, NiZn at Co site respectively and compounded by La0.7Sr0.3MnO3. The crystalline powder samples of Sr3-xCexCo2Fe24O41Sr3(NiZn)xCo2(1-x)Fe24O41and La0.7Sr0.3MnO3/Sr3Co2Fe24O41were 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, respectively. The hysteresis loops of the samples were measured by PPMS-9T-type physical properties measurement system. The room temperature resistivity of the samples was measured by cylinder method. The results showed that the samples calcined above1250℃for5hours were single Z phase ferrites which had micro-hexagonal flake shape and normal chemical ingredients. La0.7Sr0.3MnO3coated on the surface of Sr3Co2Fe24O41The magnetic properities of samples were improved, the resistivity was reduced by doping Ce at Sr site, NiZn at Co site respectively and compounding La0.7Sr0.3MnO3, and the formation went through several stages such as water evaporation, thermal decomposition and crystalline growth etc.The complex permittivity and complex permeability of the samples 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 or mass fraction and thickness on microwave reflectance of them were analysed and the electromagnetic loss mechanism were discussed. The results showed that forSr3-xCexCo2Fe24O41and Sr3(NiZn)xCo2(1-x)Fe24O41with2.40mm thickness when x=0.3, the microwave absorption peak was13.2dB at12.3GHz and25.1dB at13.5GHz, respectively, and the bandwidth above lOdB was3.3GHz and7.7GHZ, respectively, which were better than other content about microwave absorption. The absorption peak of La0.7Sr0.3MnO3/Sr3Co2Fe24O41with2.30mm thickness was27.5dB at13.7GHz and the bandwidth above lOdB was4.9GHz when the mass fraction of La0.7Sr0.3MnO3was60wt%. The magnetic losses ofSr3-xCexCo2Fe24O41and Sr3(NiZn)xCo2(1-x)Fe24O41were main but their dielectric losses weaker. La0.7Sr0.3MnO3/Sr3Co2Fe24O41had not only strong magnetic losses, but also strong dielectric losses.