Tailoring impedance match and enhancing microwave absorption of Fe3O4/Bi24Fe2O39/Bi hollow porous microrods by controlling their composition

Abstract

A self-assembly/precipitate conversion/decomposition process was developed for the controllable synthesis of Fe3O4/Bi24Fe2O39/Bi hollow porous microrods (HPMRs). The results demonstrated that the crystal size, component, and performances of HPMRs could be effectively modulated via changing Fe2+/Bi3+ molar ratio (γ). Fe3O4/Bi24Fe2O39/Bi HPMRs exhibited ferromagnetic behavior at room temperature. As Bi and Bi24Fe2O39 contents increased with γ, the saturation magnetization Ms and attenuation constantly decreased, whereas coercivity Hc and impedance matching ratio increased. Compounding Fe3O4 with small quantities of Bi and Bi24Fe2O39 into HPMRs can significantly enhance microwave absorption. Fe3O4/Bi24Fe2O39/Bi HPMRs formed at γ = 1:0.25 exhibited the optimum microwave absorption performance. The minimum RL was − 47.3 dB at 8.72 GHz, corresponding to 2.4 mm sample thickness. The absorption band with the reflection loss below − 20 dB was up to 14.0 GHz for the absorber with a thickness of 1.4 − 8.0 mm. The results demonstrate that the introduction of electromagnetic transparent materials (Bi24Fe2O39 or Bi) can improve the microwave absorption performances of Fe3O4 composites owing to enhanced impedance matching rather than attenuation constant.