スラリーを用いたフェライト多孔体電波吸収体の合成

抄録

Porous Ni_xZn_1-xFe₂O₄ and BaFe_12-x(Ti_x,Mn_x)O₁₉ ferrite materials were synthesized from wood and paper templates infiltrated ferrite slurry nitrates for the application of high frequency electromagnetic shielding. The nickel, zinc, barium and iron(III) nitrate aqueous precursor solution was infiltrated into the cedar wood specimens and were sintered at the temperature between 800 ℃ and 1400℃. From the XRD analysis, the ferrite crystallizations were recognized for the all sintered specimens, however, the secondary phase of γ-Fe₂O₃ were observed for the specimens sintered below 1000℃. From the SEM micrographs, 1-dimensional (1D) porous structure of the wood was remained in all specimens although the volume was decreased with increasing the sintered temperature. For the Ni_xZn_1-xFe₂O₄, the magnetic hysteresis loops showed the magnetic easy axis lies along the 1D pore, which evidence of the magnetic anisotropy depending on the 1D porous structure. At the present stage, the magnetic anisotropy is considered to come from the magnetic shape anisotropy like thin film structure. The real part of the complex permeability was measure up to 2 GHz and the values for the case of the 1D pore along to the magnetic field indicates larger than the case of the 1D pore perpendicular to the field and 3D porous structure. The BaFe₁₂O₁₉ porous ferrite sintered at 800℃ showed the large coercive force Hc and (B-H)_max and the H_c decreased with increasing the sintered temperature. The ferromagnetic resonance (FMR) at 9 GHz appeared at the BaFe_12-x(Ti_x,Mn_x)O₁₉ (x=3,4,5) specimens, which is the effect of the reduced anisotropy magnetic field. The FMR spectrum of the multilayered sintered BaFe_12-x(Ti_x, Mn_x)O₁₉ (x=4,5) showed the superposed spectrum of those of BaFe₈(Ti₄,Mn₄)O₁₉ and BaFe₇(Ti₅,Mn₅)O₁₉. This result indicates that the multilayered BaFe_12-x(Ti_x,Mn_x)O₁₉ can be expected for the broad band electromagnetic shields in GHz region.