Interchange core/shell assembly of diluted magnetic semiconductor CeO₂and ferromagnetic ferrite Fe₃O₄for microwave absorption

Core/shell-structured CeO2/Fe3O4and Fe3O4/CeO2nanocapsules are prepared by interchange assembly of diluted magnetic semiconductor CeO2and ferromagnetic ferrite Fe3O4as the core and the shell, and vice versa, using a facile two-step polar solvothermal method in order to utilize the room-temperature ferromagnetism and abundant O-vacancies in CeO2, the large natural resonance in Fe3O4, and the O-vacancy-enhanced interfacial polarization between CeO2and Fe3O4for new generation microwave absorbers. Comparing to Fe3O4/CeO2nanocapsules, the CeO2/Fe3O4nanocapsules show an improved real permittivity of 3-10% and an enhanced dielectric resonance of 1.5 times at 15.3 GHz due to the increased O-vacancy concentration in the CeO2cores of larger grains as well as the O-vacancy-induced enhancement in interfacial polarization between the CeO2cores and the Fe3O4shells, respectively. Both nanocapsules exhibit relatively high permeability in the low-frequency S and C microwave bands as a result of the bi-magnetic core/shell combination of CeO2and Fe3O4. The CeO2/Fe3O4nanocapsules effectively enhance permittivity and permeability in the high-frequency Ku band with interfacial polarization and natural resonance at ∼15 GHz, thereby improving absorption with a large reflection loss of -28.9 dB at 15.3 GHz. Experimental and theoretical comparisons with CeO2and Fe3O4nanoparticles are also made.