Microwave Absorption Enhancement of Multifunctional Composite Microspheres with Spinel Fe3O4 Cores and Anatase TiO2 Shells

Multifunctional composite microspheres with spinel Fe3O4 cores and anatase TiO2 shells (Fe3O4@TiO2) are synthesized by combining a solvothermal reaction and calcination process. The size, morphology, microstructure, phase purity, and magnetic properties are characterized by scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, selected-area electron diffraction, electron energy loss spectroscopy, powder X-ray diffraction, and superconducting quantum interference device magnetometry. The results show that the as-synthesized microspheres have a unique morphology, uniform size, good crystallinity, favorable superparamagnetism, and high magnetization. By varying the experimental conditions such as Fe3O4 size and concentration, microspheres with different core sizes and shell thickneses can be readily synthesized. Furthermore, the microwave absorption properties of these microspheres are investigated in terms of complex permittivity and permeability. By integration of the chemical composition and unique structure, the Fe3O4@TiO2 microspheres possess lower reflection loss and a wider absorption frequency range than pure Fe3O4. Moreover, the electromagnetic data demonstrate that Fe3O4@TiO2 microspheres with thicker TiO2 shells exhibit significantly enhanced microwave absorption properties compared to those with thinner TiO2 shells, which may result from effective complementarities between dielectric loss and magnetic loss. All the results indicate that these Fe3O4@TiO2 microspheres may be attractive candidate materials for microwave absorption applications.