Synthesis of FeNi/FeCo@C Composites with Multiple Heterointerfaces and Magnetic Phases for Low-Frequency Microwave Absorption

Magneto-dielectric composites have potential applications in efficient microwave absorption (MA) in the 2–8 GHz band. However, their development for lower-frequency applications is hindered by the complex structure–property relationship, making precise regulation of magneto-dielectric properties quite challenging. In this work, we develop high-performance microwave absorbers via rational heterointerface engineering. Guided by electromagnetic theory, we construct a functional composite material with multiple heterointerfaces and magnetic phases by introducing magnetic elements and a self-templated etching process. This tailored architecture significantly enhances the magneto-dielectric properties, leading to exceptional MA performance in the low- and midfrequency bands. The optimized FeNi/FeCo@C composites with a thickness of 2.88 mm exhibit a minimum reflection loss (RLmin) of −52.6 dB at 8.04 GHz, demonstrating strong attenuation. Furthermore, with a thickness of 4.48 mm, it achieves an RLmin of −58.9 dB at 4.68 GHz and an effective absorption bandwidth of 1.4 GHz. This work provides a feasible pathway for designing advanced MA materials for low- and medium-frequency applications through heterointerface engineering.