Enhanced Electromagnetic Wave Absorption by Bi-Layered Nano-Hollow Spheres

To cope with the increasingly serious microwave radiation pollution, an extensive search for efficient microwave absorption materials (MAMs) has attracted great attention recently. Herein, a thin layer of SiO
₂
with high dielectric permittivity on the surfaces of MnFe
₂
O
₄
(MnFO) nano-hollow spheres (NHSs) is found to be an effective strategy to improve electromagnetic (EM) wave attenuation for a larger reflection loss (RL) along with a larger bandwidth (BW) within a widely used frequency range. Larger interfacial area, higher magnetic anisotropy, internal reflections, and scattering from NHS along with higher magnetic permeability of MnFO are responsible for superior absorption properties of MnFO NHS. The MnFO (~550 nm)/SiO
₂
(~35 nm) bi-layered NHS results in a sufficiently high RL ~ −61.02 dB with a composite absorber of a thickness of only 4.40 mm and filler concentration of 20%. The above study on the variation of SiO
₂
thickness over MnFO NHSs helps us to optimize for maximum BW and absorption with minimum composite absorber thickness. This study demonstrates the optimized MnFO/SiO
₂
NHS as a highly promising low-cost and lightweight EM wave absorber suitable for high-frequency applications.