Interchange core/shell assembly of diluted magnetic semiconductor CeO₂ and ferromagnetic ferrite Fe₃O₄ for microwave absorption

Core/shell-structured CeO₂/Fe₃O₄ and Fe₃O₄/CeO₂ nanocapsules are prepared by interchange assembly of diluted magnetic semiconductor CeO₂ and ferromagnetic ferrite Fe₃O₄ as 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 CeO₂ and Fe₃O₄ for new generation microwave absorbers. Comparing to Fe₃O₄/CeO₂ nanocapsules, the CeO₂/Fe₃O₄ nanocapsules 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 CeO₂ cores of larger grains as well as the O-vacancy-induced enhancement in interfacial polarization between the CeO₂ cores and the Fe₃O₄ shells, 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 CeO₂ and Fe₃O₄. The CeO₂/Fe₃O₄ nanocapsules 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 CeO₂ and Fe₃O₄ nanoparticles are also made.