Design and wide range microwave absorption of porous Co-Co₃O₄ hybrid hollow sphere with magnetic multi-resonance mechanisms

Abstract Porous Co-Co₃O₄ hybrid hollow spheres were synthesized by a facile reduction method via hydrogen reduction of as-prepared C@Co₃O₄ solid spheres obtained by means of hydrothermal reaction between Co(NO₃)₂ and d-glucose. Owing to the consumption of amorphous carbon of C@Co₃O₄ solid spheres and the generation of metallic Co phase and oxygen vacancies in Co₃O₄ crystals during high-temperature reduction process, the electrical conductivity of the composites was increased and a higher concentration of charge carriers was produced in Co₃O₄ crystal. The imaginary permittivity dispersion behaviors have been explained based on the Cole-Cole model and the conductivity contribution model. A new simple empirical model was also supposed to find the fitted curves of the multi-resonance imaginary permeability spectrum of the composites. The electromagnetic wave can hardly be reflected on the absorber surface because of a better match between dielectric loss and magnetic loss, which originates from the combination of dielectric polarization and magnetic multi-resonance mechanisms of the special Co-Co₃O₄ hybrid nanostructures.