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 Fe 3 O 4 /Bi 24 Fe 2 O 39 /Bi hollow porous microrods (HPMRs). The results demonstrated that the crystal size, component, and performances of HPMRs could be effectively modulated via changing Fe 2+ /Bi 3+ molar ratio ( γ ). Fe 3 O 4 /Bi 24 Fe 2 O 39 /Bi HPMRs exhibited ferromagnetic behavior at room temperature. As Bi and Bi 24 Fe 2 O 39 contents increased with γ , the saturation magnetization M s and attenuation constantly decreased, whereas coercivity H c and impedance matching ratio increased. Compounding Fe 3 O 4 with small quantities of Bi and Bi 24 Fe 2 O 39 into HPMRs can significantly enhance microwave absorption. Fe 3 O 4 /Bi 24 Fe 2 O 39 /Bi HPMRs formed at γ  = 1:0.25 exhibited the optimum microwave absorption performance. The minimum R L 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 (Bi 24 Fe 2 O 39 or Bi) can improve the microwave absorption performances of Fe 3 O 4 composites owing to enhanced impedance matching rather than attenuation constant.