Zr⁴⁺doping-controlled permittivity and permeability of BaFe_12−xZr_xO₁₉and the extraordinary EM absorption power in the millimeter wavelength frequency range

Abstract

BaFe12−xZrxO19 with Zr4+ at 4f1 and 2b sites exhibits an RL of ∼−40 dB and bandwidth of ∼10 GHz at ∼0.8 mm around the millimeter wavelength atmospheric window of 35 GHz.

Formation of BaFe12−xNbxO19 and its high electromagnetic wave absorption properties in millimeter wave frequency range

“…The decreased resonance peak frequency with Nb 5+ content and temperature improving in Figure is hence ascribed to the enhanced substitution amount of Nb 5+ for Fe 3+ . The peak frequency seems to appear above 40 GHz in the sample without doping, which is accordance with the fact that the natural resonance peak frequency of pure barium ferrite is around 43.5 GHz . Besides, as is discussed, the resonance peaks in Figure originate from barium ferrite phase.…”

“…The peak intensities enhance obviously with temperature improving from 1100°C to 1300°C and Nb 5+ content increasing from x =0.2 to x =0.6 at 1300°C. Two RL peaks are revealed distinctly in the samples with x =0.4‐0.6 sintered at 1300°C under thin matching thickness of 0.84‐0.76 mm around the millimeter wave frequency of ~35 GHz, which are probably contributed by the multinatural resonance peaks in permeability and enhanced permittivity based on Equations . Considering the absorption materials usually need strong reflection loss, broad bandwidth, and thin matching thickness simultaneously for practical application, the BFNO with x =0.6 sintered at 1300°C possessing reflection loss of −42 dB, bandwidth of 11.9+ GHz, and matching thickness of 0.76 mm simultaneously exhibits the optimum absorption properties around atmospheric window of 35 GHz among all the samples.…”

“…Actually, the nature resonance peak frequency is directly proportional to H a as Equation :…”

“…where γ is the gyromagnetic ratio, g is Landé factor, and H a is anisotropy field. It is known that H a of barium ferrite is contributed by magnetic ions Fe 3+ in seriously deformed oxide polyhedrons, and the H a would decrease continuously with increasing Fe 3+ ions being substituted by nonmagnetic Nb 5+ ions . That is to say, the more the Fe 3+ ions are replaced by Nb 5+ ions, the lower the natural resonance peak frequency might be.…”

“…The barium hexaferrite BaFe 12 O 19 , a kind of versatile material, has been widely used as permanent magnet and high‐density recording media due to its high coercive force, large saturation magnetization, and corrosion resistivity . Lately, barium ferrite with Fe 3+ being substituted by ions with higher valence, such as Zr 4+ or Ti 4+ , has been suggested to use in high‐efficiency EM absorption area owing to their multiple natural resonance peaks in permeability and large permittivity contributing broad bandwidth and thin matching thickness . It implies that substituting Fe 3+ ions of barium ferrite by higher valence ions might be an effective way to develop absorption materials with extraordinary properties.…”