Lightweight ferroferric oxide nanotubes with natural resonance property and design for broadband microwave absorption

Due to strong magnetism along with low density and low percolation threshold, hollow Fe3O4 nanostructures have important potential applications in absorbing materials. In this work, Fe3O4 nanotubes with both dielectric and magnetic losses, namely bi-loss features, were obtained through two-step chemical methods (hydrothermal method and activated carbon reduction). The Fe3O4 nanotubes show high dielectric loss due to the electronic relaxation polarization, and the concentration dependence of dielectric properties for Fe3O4 nanotubes composite can be well described by the effective dielectric theory. In comparison with bulk Fe3O4 with natural ferromagnetic resonance around 1.2 GHz, the as-prepared Fe3O4 nanotubes present a natural resonant peak at 4 GHz frequency, leading to the higher magnetic loss in the radar band (2–18 GHz). Therefore, the Fe3O4 nanotubes show better microwave absorption with minimum reflection loss up to −50.94 dB compared with other Fe3O4 nanostructures. Moreover, double loss peaks were observed in 70 and 80 wt% samples with thickness of 5 mm, making this material a good candidate for designing broadband metastructure absorber.