Microwave absorption properties of a double-layer absorber based on nanocomposite BaFe₁₂O₁₉/α -Fe and nanocrystalline α -Fe microfibers

The nanocomposite BaFe₁₂O₁₉/α -Fe and nanocrystalline α -Fe microfibers with diameters of 1-5 μm, high aspect ratios and large specific areas are prepared by the citrate gel transformation and reduction process. The nanocomposite BaFe₁₂O₁₉/α -Fe microfibers show some exchange-coupling interactions largely arising from the magnetization hard (BaFe₁₂O₁₉) and soft (α -Fe) nanoparticles. For the microwave absorptions, the double-layer structures consisting of the nanocomposite BaFe₁₂O₁₉/α -Fe and α -Fe microfibers each exhibit a wide band and strong absorption behavior. When the nanocomposite BaFe₁₂O₁₉/α -Fe microfibers are used as a matching layer of 2.3 mm in thickness and α -Fe microfibers as an absorbing layer of 1.2 mm in thickness, the optimal reflection loss (RL) achieves -47 dB at 15.6 GHz, the absorption bandwidth is about 12.7 GHz ranging from 5.3 to 18 GHz, exceeding -20 dB, which covers 72.5% C-band (4.2-8.2 GHz) and whole X-band (8.2-12.4 GHz) and K_u-band (12.4-18 GHz). The enhanced absorption properties of these double-layer absorbers are mainly ascribed to the improvement in impedance matching ability and microwave multi-reflection largely resulting from the dipolar polarization, interfacial polarization, exchange-coupling interaction, and small size effect.