Sol–gel synthesis, electromagnetic properties and microwave absorption behavior of strontium Co2Z hexaferrites

Owing to the special planar structure and very high resistivity, Z-type hexaferrites possess the high initial permeability and cut-off frequency, indicating great application potential in high-frequency devices. Strontium Co2Z hexaferrites (Sr3Co2Fe24O41) were successfully prepared by the sol–gel method and calcined at the different temperatures from 1175∘C to 1250∘C. The influence of the calcined temperatures on the microstructure, phase structures, magnetic properties and microwave absorption behavior of all samples was investigated in detail. All results indicated that strontium hexaferrites go through the M-, Y-, Z-, and W-phase transformation process from 1175∘C to 1250∘C, and S-1200 (calcined at 1200∘C) is confirmed to be Co2Z-type hexaferrites. S-1200 showed the highest imaginary permeability while the imaginary permittivity of all samples is close to zero, indicating the excellent microwave adsorption behavior of strontium Co2Z hexaferrites. The reflection loss results indicate that S-1200 exhibits the best microwave absorption performance with the RL value of −32.4 dB for 4.0 mm thickness at 4.72 GHz, according to the impedance matching and quarter-wavelength theory.