Microwave absorption properties of single- and double-layer absorbers based on electrospun nickel–zinc spinel ferrite and carbon nanofibers

Ni–Zn spinel ferrite nanofibers (NFs) with the chemical formula M2xNi0.5−xZn0.5−xFe2O4 (M = Co or Cu, and x = 0 or 0.1) and carbon nanofibers (CNFs) were fabricated through electrospinning technique and subsequent thermal treatment processes. Microwave absorption properties of single-layer and double-layer absorbers based on M2xNi0.5−xZn0.5−xFe2O4 NFs and CNFs were investigated in the frequency range of 2–18 GHz. The single-layer absorbers based on Ni–Zn spinel ferrite NFs show strong microwave absorbing abilities, and the minimum reflection loss (RL) for Ni0.5Zn0.5Fe2O4, Co0.2Ni0.4Zn0.4Fe2O4 and Cu0.2Ni0.4Zn0.4Fe2O4 NFs is − 77.5, − 57.8 and − 69.8 dB with a matching thickness of 5.0, 4.5 and 5.5 mm, respectively. The double-layer absorbers exhibit better absorption performances with a stronger microwave absorption and a wider effective absorption bandwidth (RL < − 10 dB) in comparison with the single-layer absorbers at the same thickness. The optimized double-layer absorber with a total thickness of 3 mm has an optimal RL value less than − 115.9 dB and a maximum absorption bandwidth of 12.4 GHz ranging from 5.6 to 18 GHz. While the corresponding single-layer absorber with a thickness of 3 mm has a minimum RL value of − 21.2 dB and an effective absorption bandwidth of 9.8 GHz. The significantly enhanced microwave absorption performance for double-layer absorbers should be attributed to the good cooperation effect of Ni–Zn spinel ferrite NFs (with high magnetic loss) and CNFs (with strong dielectric loss) as well as the improved impedance matching characteristics. It is expected that our double-layer absorbers can be a good reference for the design of new high performance microwave absorbing materials.