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 Fe 3 O 4 nanostructures have important potential applications in absorbing materials. In this work, Fe 3 O 4 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 Fe 3 O 4 nanotubes show high dielectric loss due to the electronic relaxation polarization, and the concentration dependence of dielectric properties for Fe 3 O 4 nanotubes composite can be well described by the effective dielectric theory. In comparison with bulk Fe 3 O 4 with natural ferromagnetic resonance around 1.2 GHz, the as-prepared Fe 3 O 4 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 Fe 3 O 4 nanotubes show better microwave absorption with minimum reflection loss up to −50.94 dB compared with other Fe 3 O 4 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.