Adjustable electromagnetic properties of FeNi/Fe/C-based composites derived from controllable carbothermal reduction

In order to optimize microwave absorption performance at low matching thickness, polyvinyl pyrrolidone-induced carbothermal reduction has been utilized to successfully convert NiFe 2 O 4 /Fe 2 O 3 /Ni composite spheres into FeNi/Fe/C-based composites. The results show that with the increase dosage of polyvinyl pyrrolidone, the reduction degree would first increase and then decrease, which leads to the change of composition and morphology. In detail, Fe 3 O 4 can be found in S-0.3, S-0.4, and S-0.6, revealing lower reduction degree. And S-0.5 contains only FeNi, Fe, and C, indicating highest reduction degree. Moreover, smooth carbon layers can be observed on the particle surface for S-0.5, while the other samples exhibit rough surface decorated with particle clusters. The changing trend of graphitic degree is in line with reduction degree, and saturation magnetization basically increases with the increase dosage of polyvinyl pyrrolidone. As for electromagnetic properties, S-0.5 possesses strongest dielectric loss and magnetic loss, while the other samples own similar loss ability except in high frequency range, which should be ascribed to dielectric relaxation. Owing to synergetic effect of conduction loss, interfacial polarization, dipolar polarization, natural resonance, exchange resonance, eddy current loss, and appropriate impedance, the as-synthesized FeNi/Fe/C-based composites hold great potential in evading radar detection and reducing electromagnetic pollution. This work may offer novel insights into the design and application of high-performance magnetic metal-based microwave absorbing materials derived from controllable reduction of ferrites.