Excellent absorption properties of BaFe12-xNbxO19 controlled by multi-resonance permeability, enhanced permittivity, and the order of matching thickness

For the sol-gel-derived BaFe12-xNbxO19 (x = 0-0.6), coercivity (H-c) and saturation magnetization (M-s) vary from 3.53-0.85 kOe and 70.3-53.8 emu g(-1) to 1.02-0.22 kOe and 69.6-59.5 emu g(-1), respectively, with an increase in sintering temperature from 1250 degrees C to 1350 degrees C. Moreover, epsilon' and epsilon '' increase from 4.13-4.04 and 0.0049-0.0045 to 7.64-6.93 and 1.50-0.97 over 26.5-40 GHz, and the multi-resonance peaks in permeability shift from similar to 40+ GHz to similar to 27 GHz. The bandwidth (BW) and reflection loss peak intensity (RLp) are broadened and enhanced from 0.8 GHz and -10.3 dB of the sample with x = 0.2 sintered at 1250 degrees C under 0.92 mm to 11.9+ GHz and -54 dB, respectively, of the sample with x = 0.6 sintered at 1350 degrees C under 0.86 mm around a millimeter-wave atmospheric window of 35 GHz. The effects of Nb5+ content (x) and sintering temperature on grain size, phase compositions, formations of Fe2+ and oxygen vacancy, and thus on static magnetism and EM parameters are investigated. The correlations of multi-resonance permeability, enhanced permittivity, and the order of matching thickness with absorption properties are also discussed in detail.