Electromagnetic wave attenuation properties of MFe_2O_4 (M = Mn, Fe, Co, Ni, Cu, Zn) nano-hollow spheres in search of an efficient microwave absorber

摘要

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 MFe_O_4 [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, M~(2+) [M = Mn, Co, Ni, Cu, Zn] substitution in Fe_3O_4 displays a clear enhancement of EM absorption properties compared to traditional magnetite where MnFe_2O_4 NHS is found to exhibit an optimal reflection loss(RL) of about - 32.7 dB, total shielding efficiency (SE_(Total))～-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%, MnFe_2O_4 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 (t_m) displays a good agreement between experimental and simulated t_m values. The overall results indicate that ferrites in the form of hollow structures are much more efficient than their bulk counterpart and optimized MnFe_2O_4 NHS is found to be most suitable for high-frequency applications as an efficient low-cost microwave absorber.