Synthesis of Fe–ferrite composite nanotubes with excellent microwave absorption performance

Fe–ferrite composite nanotubes were successfully prepared by thermal hydrogen reduction of α-FeOOH nanowires. The nanotubes have diameters of about 100 nm and lengths of tens of micrometres. The formation mechanism of Fe–ferrite composite nanotubes is discussed, and the non-equilibrium diffusion between hydrogen and oxygen was found to be responsible for the formation of the hollow interior structure. Because of the high shape anisotropy of the 1-D shape, the coercivity of composite nanotubes was higher than that of reported granular Fe–ferrite composite nanoparticles. Since the eddy current is effectively suppressed by the thin wall characteristic of nanotubes, the composite nanotubes exhibit higher permeability than that of the reported ferromagnetic metal nanowires. Due to the better impedance matching and higher dissipation efficiency, a superior microwave absorption performance was obtained in Fe–ferrite composite nanotubes, in which the maximum reflection loss is −18 dB and the effective absorption band (<−10 dB) covers the entire frequency band of 12.5–17.5 GHz.