Optimized impedance matching and enhanced microwave absorbing performance of porous flaky Fe4N wrapped with SiO2

Abstract

The flaky porous Fe4N@SiO2 particles were prepared by nitriding Fe2O3@SiO2 which was fabricated by hydrothermal synthesis and sol-gel coating treatment. The structure, morphology, magnetostatic and electromagnetic properties of the Fe4N@SiO2 particles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), vibrating sample magnetometer (VSM) and vector network analyzer (VNA). For comparison, the flaky Fe4N particles without SiO2 shell were prepared by nitriding Fe2O3 and characterized by the same technologies. The results show that the SiO2 shell enhances the interface polarization effect on Fe4N and effectively adjusts the relative permittivity, which brings a much better impedance matching for Fe4N@SiO2 than Fe4N. The minimal reflection loss (RL) of the Fe4N@SiO2 can reach −27.8 dB with a thickness of 2.0 mm and −23.7 dB with a thickness of only 1.5 mm. By contrast, the RL values of Fe4N without SiO2 shell are more than −2.2 dB at the whole frequency range of 2 ~ 18 GHz. The influence mechanism of SiO2 dielectric shell on the microstructure and properties was revealed. This work gives a remarkable proof that coating a dielectric shell on the high conductive ferromagnetic cores is an effective way to obtain microwave absorbers with enhanced absorption performance.