Jing Maoxiang

Enhancement of microwave absorption of nanocomposite BaFe12O19/α-Fe microfibers

Nanocomposite BaFe12O19/α-Fe microfibers with diameters of about 1–5 μm are prepared by the organic gel-thermal selective reduction process. The binary phase of BaFe12O19 and α-Fe is formed after reduction of the precursor BaFe12O19/α-Fe2O3 microfibers at 350 °C for 1 h. These nanocomposite microfibers are fabricated from α-Fe (16–22 nm in diameter) and BaFe12O19 particles (36–42 nm in diameter) and basically exhibit a single-phase-like magnetization behavior, with a high saturation magnetization and coercive force arising from the exchange-coupling interactions of soft α-Fe and hard BaFe12O19. The microwave absorption characteristics in a 2–18 GHz frequency range of the nanocomposite BaFe12O19/α-Fe microfibers are mainly influenced by their mass ratio of α-Fe/BaFe12O19 and specimen thickness. It is found that the nanocomposite BaFe12O19/α-Fe microfibers with a mass ratio of 1:6 and specimen thickness of 2.5 mm show an optimal reflection loss (RL) of −29.7 dB at 13.5 GHz and the bandwidth with RL exceeding −10 dB covers the whole Ku-band (12.4–18.0 GHz). This enhancement of microwave absorption can be attributed to the heterostructure of soft, nano, conducting α-Fe particles embedded in hard, nano, semiconducting barium ferrite, which improves the dipolar polarization, interfacial polarization, exchange-coupling interaction, and anisotropic energy in the nanocomposite BaFe12O19/α-Fe microfibers.

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 Ku-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.