Abstract
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.
Highlights
The integration of microwave absorbers in electronic devices and systems has become an essential strategy in minimizing electromagnetic (EM) radiation and improving EM compatibility.[1]
We report the use of a facile two-step polar solvothermal method to prepare two different types of core/shell-structured bi-magnetic nanocapsules by interchange assembly of diluted magnetic semiconductor CeO2 and ferromagnetic ferrite Fe3O4 as the core and the shell (i.e., CeO2/Fe3O4 nanocapsules) and vice versa (i.e., Fe3O4/CeO2 nanocapsules)
As O-vacancies can affect the polarity of the CeO2 lattice, the interfacial polarization between CeO2 and Fe3O4 should have a relationship with the concentration of O-vacancies in CeO2 near the interface.[17]
Summary
The integration of microwave absorbers in electronic devices and systems has become an essential strategy in minimizing electromagnetic (EM) radiation and improving EM compatibility.[1]. Shells have been proposed in the core/shell and even core/double-shell structure.[4,5,6,7,8,9] In addition to combining different core and shell material phases, the effect of interchange core and shell on the microwave absorption properties has ignited new research interest and direction in more recent years.[4,5,7] From a physical perspective, the distinct dielectric, electrical, and/or magnetic properties of these shells will lead to characteristically different interfacial effects and microwave absorption properties.[9] Multiferroic, semiconducting, insulating/conducting, conducting/insulating, etc. shells have been proposed in the core/shell and even core/double-shell structure.[4,5,6,7,8,9] In addition to combining different core and shell material phases, the effect of interchange core and shell on the microwave absorption properties has ignited new research interest and direction in more recent years.[4,5,7] From a physical perspective, the distinct dielectric, electrical, and/or magnetic properties of these shells will lead to characteristically different interfacial effects and microwave absorption properties.[9]
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