Enhanced interfacial polarization relaxation effect on microwave absorption properties of submicron-sized hollow Fe₃O₄hemispheres

Bowl-like Fe3O4 hemispheres with a hollow structure have been synthesized with an average outer diameter of 250 nm and a shell thickness of 80 nm using tiny ~25 nm Fe3O4 nanoparticles. The complex permittivity, complex permeability and reflection loss of the samples in weight percentages of 60% of the hollow Fe3O4 hemispheres were studied by using an Agilent E5071 C vector network analyzer in the frequency range of 2–18 GHz. Results show that as-prepared samples exhibit improved microwave absorbing properties compared with our previously reported ball-like Fe3O4 microspheres and Fe3O4 hemispheres/r-GO composites. Two Cole–Cole semicircles reveal that there are dual dielectric relaxation losses: one is interfacial polarization relaxation, the other is dipolar relaxation. X-ray photoelectron and Fourier transform infrared spectra of the products calcinated at different temperatures reveal the enhanced interfacial polarization relaxation effect due to the higher concentration of Fe2+ ions in the surface layer and increased interfaces among the Fe3O4 nanoparticles that form the submicron-sized hollow Fe3O4 hemispheres. In addition, the fitted results of complex permeability demonstrate that the magnetic loss is mainly caused by the Kittel natural resonance.