Enhancement of low-frequency microwave absorption in TiO2@Fe-based amorphous alloy composite powders

The development of materials with good absorption properties at low-frequency microwave band has been challenged for many years. Combinations of magnetic/dielectric materials are desirable, but the introduction of a dielectric component normally reduce the magnetic loss caused by magnetic dilution. Here, an effective method is reported to reduce the dielectric constant of the sample without significantly reducing the permeability. In this study, TiO2@Fe-based amorphous alloy composite powders have been prepared by magnetron sputtering and subsequent oxidation, and their microwave absorption properties at 1-4 GHz and their mechanisms have been investigated in detail. The results show that the surfaces of the prepared composite powders are partial region covered with very thin layer of TiO2. The very low amount of TiO2 (less than 0.2wt% in Ti element content) achieves a significant reduction in the dielectric constant of the sample with barely change in the morphology and phase structure of the powders, while the magnetic permeability remains unchanged or even increases slightly. Low-frequency microwave attenuation capability can be effectively optimised by adjusting the sputtering time. Compared with Fe-based amorphous alloy powders, EAB of 1.74 GHz and RLmin of - 32.84 dB can be obtained from TiO2@Fe-based amorphous alloy composites powders, which represents a 141.7% broadening of EAB with a 102.7% increase in RLmin. This method provides a new perspective for preparation of microwave absorbing materials with high performance in low-frequency band.