Synthesis And Electromagnetic Properties Of BaFe₁₂O₁₉ And Its Composite Materials

M-type BaFe₁₂O₁₉ is not only a hard magnetic material with c-axis anisotropy,but also a good electromagnetic wave absorbing material.However,when BaFe₁₂O₁₉ is used alone as an absorbent,there are some problems,such as poor conductivity,large specific gravity,narrow absorbing band and so on.The effects of doping rare earth element La on the magnetic properties of BaFe₁₂O₁₉ were systematically studied in this thesis.The magnetic and absorbing properties of La_0.15Ba_0.85Fe₁₂O₁₉/C and La_0.15Ba_0.85Fe₁₂O₁₉/PANI composites were studied.The phase,microstructure,magnetic properties,electromagnetic parameters and microwave absorption properties of La_xBa_1-xFe₁₂O₁₉,La_0.15Ba_0.85Fe₁₂O₁₉/C and La_0.15Ba_0.85Fe₁₂O₁₉/PANI were characterized and analyzed by X-ray diffractomer?XRD?,scanning electron microscope?SEM?,vibrating sample magnetometer?VSM?and vector network analyzer?VNA?.At first,pure barium ferrite were synthesized by hydrothermal method under n(Ba²⁺)/n(Fe³⁺)=1:8 at 220 ? for 6 h.Then,La³⁺ doped barium ferrite were prepared by hydrothermal method while the doping ratio x was 0.05,0.10,0.15,0.20,0.25.The effects of La³⁺ content on the magnetic properties of La_xBa_1-xFe₁₂O₁₉ were studied.The results showed that the solid solubility of La³⁺ was 0.15,and the saturation magnetization magnetization?Ms?and the remanent magnetization?Mr?of the samples reached the maximum.Secondly,La_0.15Ba_0.85Fe₁₂O₁₉/C composites were successfully synthesized by hydrothermal method by using glucose as carbon source.The effects of C content on the morphologies and electromagnetic properties of the composites were studied.The results showed that the grain size?D?,Ms and Mr of La_0.15Ba_0.85Fe₁₂O₁₉/C decreased with the increase of the content of C.La_0.15Ba_0.85Fe₁₂O₁₉/C sample had the best absorbing performance with the addition of 1 g La_0.15Ba_0.85Fe₁₂O₁₉ and the maximum reflection loss reached-8.5 dB in the range of 15-16 GHz while the thickness was 3 mm.Last,the La_0.15Ba_0.85Fe₁₂O₁₉/PANI composites were successfully prepared by in situ polymerization method.The results showed that D,Ms and Mr of the composites decreased with the increase of the content of PANI.The conductivity of the composites increased with the increase of PANI ratios.The microwave absorbing property of La_0.15Ba_0.85Fe₁₂O₁₉/PANI was best when the content of La_0.15Ba_0.85Fe₁₂O₁₉ sample is 0.51 g,and the maximum reflection loss reached-10.7 dB in the range of 12-13 GHz,and moved to low-frequency direction while the thickness was 3 mm.