Microwave Absorption Characteristics of M2+, 3+ (M = Mn3+, Zn2+, Ni2+)-substituted Sr3Co2Fe24O41 Hexaferrite Composites

Mn, Zn, Ni-substituted Z-type hexaferrites, Sr3Co2Fe24O41 (Sr3Co2Fe24-xMnxO41, Sr3Co2-yZnyFe24O41, Sr3Co1-zNizZnFe24O41), were prepared by sol-gel synthesis processes and their high-frequency magnetic, dielectric and electromagnetic (EM) wave absorption characteristics were investigated. Substituting Mn for Fe by x = 0.5 maintained the single-phase Z phase while shifting the μ' , μ″ spectra towards lower frequencies. Substituting Zn for Co by y = 1.0 resulted in the single-phase Z phase and effectively shifted the μ' , μ″ spectra towards lower frequencies. Additionally, substituting Ni by z = 0.5, 1.0 gradually shifted the μ' , μ″ spectra towards higher frequencies. The Sr3Co2Fe24O41 with a single Z-type hexaferrite phase and epoxy (10 wt.%) composite showed strong ferromagnetic resonance (FMR) at 3.05 GHz and exhibited primary and secondary strong EM wave absorption characteristics at the thicknesses where impedance matching occurred near the FMR frequency and at frequencies higher than this. Substitution of Mn and Zn tended to decrease the FMR frequency, while substitution of Ni tended to increase it. The samples with substituted compositions also showed changes in the primary and secondary strong EM wave absorption frequency regions, depending on the FMR frequency changes. They demonstrated excellent EM wave absorption performance with the absolute value of the minimum reflection loss (RLmin) ranging from 42 to 58 dB. The FMR-tunable Z-type hexaferrite is a promising EM wave absorption material that can modulate EM wave absorption characteristics by cation substitution in in L-S-band (1~4 GHz) and X-band (8~12 GHz) ranges.