Electromagnetic wave attenuation properties of MFe2O4 (M = Mn, Fe, Co, Ni, Cu, Zn) nano-hollow spheres in search of an efficient microwave absorber

Abstract

In search of light-weight, stable, cost-effective and efficient microwave absorbing material, here, we have investigated electromagnetic wave (EM) attenuation properties of transition metal based MFe2O4 [M = Mn, Fe, Co, Ni, Cu, Zn] nano-hollow spheres in-detail within a widely-used frequency range of 1–20 GHz. The divalent cation, M2+ [M = Mn, Co, Ni, Cu, Zn] substitution in Fe3O4 displays a clear enhancement of EM absorption properties compared to traditional magnetite where MnFe2O4 NHS is found to exhibit an optimal reflection loss (RL) of about − 32.7 dB, total shielding efficiency (SETotal) ~ −42 dB and a high attenuation constant (α) ~ 196 Np/m. Favorable impedance matching, significant dielectric and magnetic loss contribute to the enhancement in absorption properties. Interestingly, with increase in filler concentration (in epoxy resin matrix) from 0 wt% to 50 wt%, MnFe2O4 NHS shows a gradual increase in RL values and an excellent RL of about − 45.6 dB at thickness ~4.2 mm is obtained for 50 wt% composite with a total effective bandwidth (RL < −10 dB i.e. absorption >90%) of ~3.6 GHz. Moreover, analysis of quarter-wavelength model for best matching thickness (tm) displays a good agreement between experimental and simulated tm values. The overall results indicate that ferrites in the form of hollow structures are much more efficient than their bulk counterpart and optimized MnFe2O4 NHS is found to be most suitable for high-frequency applications as an efficient low-cost microwave absorber.