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The Understanding of Size-Dependent Magnetic Loss Mechanisms Based on Surface Atoms Moment to Tune Electromagnetic
Lei Ge1, Guifang Zheng1, Ke Yang1
1Department of Physics, Beijing Technology and Business University, Beijing, China.
Abstract:
Magnetic loss is a key mechanism in electromagnetic wave (EMW) absorption, but it is still a challenge to understand the relationships between the size effect and magnetic loss ability. Here, we synthesized Fe3O4@CeO2 core-shell composites to reveal the above relationship. Our synthesis started with the preparation of Fe2O3 nanocubes, followed by coating CeO2 shell by hydrothermal technology. After undergoing H2 reductive annealing, Fe3O4@CeO2 core-shell nanocubes were obtained with their magnetic core size fixed to 155 ± 10 nm, 305 ± 10 nm, 510 ± 15 nm, and 705 ± 15 nm, respectively, where CeO2 shell can stabilize the magnetic cores against agglomeration and adjust the dielectric feature. Within 2-6 GHz, the smallest-sized Fe3O4@CeO2 represents the highest magnetic loss ability by the natural resonance for the largest number of surface atoms. Within 6-14 GHz, the exchange resonance from the Fe2+-O-Fe2+ super-exchange interactions is suppressed by the increased oxygen vacancies and super-exchange distances for the small-sized particles. As a result, the largest-sized Fe3O4@CeO2 achieved an effective absorption bandwidth of 5.7 GHz (8.1-13.8 GHz) for the medium-frequency application. Our work clarifies the key role of surface atom moment in magnetic loss, offering guidance for understanding the relationship among size-mechanism-performance.
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