Zr4+ doping-controlled permittivity and permeability of BaFe12-xZrxO19 and the extraordinary EM absorption power in the millimeter wavelength frequency range

摘要

M-type barium ferrite powders doped with Zr4+ ions (BaFe12-xZrxO19 x = 0-0.4), possessing high permittivity and multi-resonant permeability, were synthesized by the sol-gel process. The single-phase hexagonal plate-like barium ferrites were formed with Zr4+ substituting Fe3+ at the 4f(1) sites initially and then at the 2b sites afterwards with increasing doping content. The H-a of the ferrites decreased from 15.75 kOe to 8.13 kOe with increasing Zr4+ from x = 0 to 0.4. The epsilon' and epsilon" of the ferrite with Zr4+ doping were increased to 7.7-6 and 3.4-1.5 over 18-40 GHz from 5.8-5 and 0.7-0.4 without doping, respectively. Contributed mainly by the enhanced permittivity, the matching thicknesses of the Zr4+ ions doped ferrites were as low as only similar to 1 mm or below, i.e. 1.5-3 times thinner than those reported recently. The complex permittivity was still close to the complex permeability in the doped ferrites. Hence, a strong reflection loss of similar to-50 dB could be attained and the absorptivity of electromagnetic (EM) power per unit thickness reached as high as 0.156% mu m(-1), i.e. 2-5 times higher than those of novel absorbing materials. The multi-resonance permeability peaks originated from Fe3+ ions, and exchange couplings among Fe3+, Fe2+ and O- contributed multiple reflection loss peaks and thus, a broad bandwidth of similar to 12 GHz (RL < -10 dB), which was 2-4 times broader than those normally reported. Consequently, the Zr4+-doped barium ferrites are promising for use as excellent absorbing materials in the millimeter wavelength frequency range.