Exceeding natural resonance frequency limit and enhanced microwave absorption performance of Fe3O4 nanorods coated with SiO2 layer

Fe 3 O 4 @SiO 2 composites with different morphologies (hollow nanorods , porous nanorods, and flower-like nanoparticles) were constructed using different preparation methods. Considerably enhancement of resonance frequency and permeability beyond Snoek’s limitation were observed in the Fe 3 O 4 @SiO 2 composites with shape anisotropy and porous core-shell nanostructure . The resonance frequency of porous Fe 3 O 4 @SiO 2 nanorods enhanced to 4.21 GHz, which is much higher than the natural resonance frequency of 1.2 GHz for Fe 3 O 4 bulk. The minimum reflection loss (RL min ) of Fe 3 O 4 @SiO 2 porous nanorods reached -59.49 dB at 8.89 GHz, and its effective bandwidth (RL < -10 dB) covered 4.52 GHz at a thickness of 3.18 mm. In addition, the radar scattering cross section (RCS) reduction value reached more than 48 dBm 2 after removing the background. Our study provides insight into the relationship between anisotropy, core-shell structure, morphology of nanoparticles and corresponding microwave performance, and provides a reference scheme for the fabrication of high-performance lightweight microwave absorbing materials.