Excellent microwave absorption performances of cobalt-doped SrFe12O19 hexaferrite with varying incident angles

Abstract

The rapid development of electronic technology and wireless communication for electronic equipment is crucial for civilian and military fields nowadays. However, it has been generating electromagnetic (EM) radiation pollution, which has recently gained more attention. Cobalt-doped SrFe12O19 (Co-SrM) samples, which were predicted to be excellent microwave-absorbing materials (MAMs), were successfully prepared using a ball milling method followed by heat treatment. Samples were formed into polygonal shapes with a crystallite size of ∼24 nm and an average grain size of 160−200 nm. The saturation magnetization (Ms) increased with the increase in Co concentration, whereas coercivity (Hc) showed an inverse tendency. The doping also resulted in variations and fluctuations in EM properties, which affected their microwave absorption properties. All Co-SrM-epoxied samples showed good microwave absorption performances in the frequency and thickness ranges of 12−18 GHz (Ku band) and 4−6 mm, respectively. The best value of reflection loss (RL) was −30.7 dB, meaning that ∼99.9% of the incident wave was absorbed. The excellent microwave absorption performance could be attributed to impedance matching, natural resonance, eddy current effects, and dielectric relaxation loss. In both transverse electric and magnetic polarization modes, Co-SrM-epoxied samples maintained (even improved) the RL values with the large incident angle of 0−60° for the Ku band. In addition, Co-SrM-epoxied samples also enhanced the microwave absorption performance in the C and X bands (4 −12 GHz) with an incident angle of 80−89°. These results proved that Co-SrM epoxied samples could be applied as promising MAMs for practical applications.