Development of high-efficiency tri-layer microwave absorbing materials based on SrMeFe11O19 hexaferrite

Recently, electronic devices have become an essential part of daily life as well as national defense. Along with their use and convenience, the electromagnetic (EM) radiation generated by them is a new pollutant that should be mitigated. SrMeFe11O19 (Me = Fe, Zn, and Co) samples were successfully prepared with the expectation of being high-efficiency microwave absorbers. Samples were crystallized into the M-type hexaferrite phase with an average crystallite size of 24-26 nm and an average grain size in the range of 160-220 nm. The change in doping element also modified static magnetic and EM properties, leading to their differences in microwave absorption properties. SrFeFe11O19 and SrCoFe11O19 samples showed reflection loss (RL) values of -25.7 and -15.9 dB for the same thickness of 5.50 mm, respectively. Meanwhile, the SrZnFe11O19 sample had RL = -25.5 and -28.8 dB for thicknesses of 1.50 mm and 5.00 mm, respectively. The good microwave dissipation features of these samples could be attributed to good impedance matching, excellent attenuation constants, and a large number of dynamic processes of dielectric loss. The tri-layer MAMs fabricated from SrMeFe11O19 samples even showed more impressive microwave absorption performance with higher RL values for lower matching thicknesses. SrFeFe11O19/SrZnFe11O19/SrCoFe11O19 and SrCoFe11O19/SrZnFe11O19/SrFeFe11O19 with layer thicknesses of 2/2/1 (mm) could reach RL values of -39.4 and -48.0 dB, respectively. Meanwhile, tri-layer absorbers of SrFeFe11O19/ SrCoFe11O19/SrZnFe11O19 and SrCoFe11O19/SrFeFe11O19/SrZnFe11O19 with layer thicknesses of 1/1/3 (mm) could reach RL values of -44.9 and -46.3 dB, respectively. These excellent RL values could be attributed to the synergistic effects of three layers, which provided an easy approach to improving the microwave absorption performances of as-prepared materials. These results would be beneficial for practical applications, such as covering weapons with different types of microwave-absorbing paint to make them invisible on enemy radars.