An Ion‐Engineering Strategy to Design Hollow FeCo/CoFe2O4 Microspheres for High‐Performance Microwave Absorption

Abstract

AbstractAlthough assembled hollow architectures have received considerable attention as lightweight functional materials, their uncontrollable self‐aggregation and tedious synthetic methods hinder precise construction and modulation. Therefore, this study proposes a bi‐ion synergistic regulation strategy to design assembled hollow‐shaped cobalt spinel oxide microspheres. Dominated by the coordination‐etching effects of F− and the hydrolysis‐complex contributions of NH4+, the unique construction is formed attributed to the dynamic cycles between metal complexes and precipitates. Meanwhile, their basic structures are perfectly retained after reduction treatment, enabling FeCo/CoFe2O4 bimagnetic system to be obtained. Subsequently, in‐depth analyses are conducted. Investigations reveal that multiscale magnetic coupling networks and enriched air‐material heterointerfaces contribute to the remarkable magnetic‐dielectric behavior, supported by the advanced off‐axis electron holography technique. Consequently, the obtained FeCo/CoFe2O4 composites exhibit excellent microwave absorption performances with minimal reflection losses (RLmin) as high as −51.6 dB, an effective absorption bandwidth (EAB) of 4.7 GHz, and a matched thickness of 1.4 mm. Thus, this work provides an informative guide for rationally assembling building blocks into hollow architectures as advanced microwave absorbers through bi‐ion and even multi‐ion synergistic engineering mechanisms.