Magnetic and electromagnetic characterization of barium hexaferrite ceramics and their polymer matrix composites /

Kaya, Seray
In this study, BaHF-based polymer matrix composites were prepared as potential EM wave absorbing materials. Firstly, BaHF powders and platelets were synthesized by mixed oxide method and by molten salt synthesis (MSS) technique, respectively, which were further used as additives in the EM wave absorbing composites. The effect of molten salt composition on the amount of BaHF phase formation, as well as, on the morphology and magnetic properties of the final products were discussed according to the characterization results. Quantitative XRD results showed that with the increase in NaCl flux content, BaHF formation was enhanced and the highest conversion (97.8 wt%) was obtained in the case of 100 wt% NaCl flux. Corners of the BaHF platelets in NaCl flux were rounded, while KCl flux produced sharp edge platelets. Increasing NaCl content in the flux improved the coercivity and remnant magnetization of BaHF, leading to a more pronounced hard magnetic behavior. vi In the second part of the study, BaHF-based polymer matrix composites were prepared by tape casting method, and their electromagnetic wave absorption potentials were investigated within 18-40 GHz frequency range by free-space measurement method. Effect of BaHF content and alignment on the EM wave properties was investigated. To enhance the EM wave absorption potential of the resulting composites, graphite or nickel flakes were incorporated into polymer matrix, and multilayered composites were produced. BaHF-Ni flake containing composites revealed 50-75% EM wave absorption in 18-40 GHz range with the synergistic effect of the magnetic and ohmic loss effective in the structure.