Enhancement of electromagnetic wave absorption in MnFe2O4 nano-hollow spheres

In order to obtain a light-weight, stable, and cost-effective yet efficient electromagnetic (EM) wave absorbing material, here, we investigated EM wave attenuation properties of as-synthesized low-density MnFe2O4 nano-hollow spheres (NHS) in-detail, varying their sizes [mean diameter (in nm) of sample sets=100, 220, 300, 450, and 550] within a widely used frequency range of 1-20GHz. In addition to larger interfacial area and magnetic anisotropy of NHSs, multiple internal reflections in its hollow core promote better EM wave absorption. Therefore, tuning of NHS sizes is demonstrated as an effective strategy to achieve an excellent microwave absorber, and MnFe2O4 NHS of diameter similar to 450nm is found to exhibit a maximum reflection loss (RL) of approximately -52.6dB, total shielding efficiency (SETotal) of approximately -39.5dB, and a high attenuation constant (alpha) of similar to 285Np/m due to best impedance matching, |Z(in)/Z(0)|similar to 1, along with significant dielectric and magnetic losses. Furthermore, a thickness-dependent study on 450nm NHS composites reveals that optimum RL reached approximately -55.4dB at 9.6GHz for t=5.1mm with a broad total effective bandwidth (RL<-10dB, i.e., attenuation >90%) of similar to 3.7GHz. Moreover, the analysis from the quarter-wavelength model for best matching thickness (t(m)) displays a good agreement between experimental and calculated t(m) values. This study presents optimized 450nm MnFe2O4 NHS at much lower filler concentration (only 20wt.% in the epoxy resin matrix) as a highly promising low-cost and light-weight microwave absorber suitable for practical high-frequency applications.

Automated summary

By tuning the sizes of MnFe2O4 nano-hollow spheres, excellent microwave absorbing materials can be achieved, with the 450nm diameter sample exhibiting the best performance for high-frequency applications.