Fabrication of Electromagnetic Absorber Composed of Ferrite Particles with Shape Anisotropy

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A wide-band electromagnetic absorber composed of ferrite particles with shape anisotropy has been described.Conditions for obtaining acicular and platy ferrite particles by the flux method were determined. Ferrite-polymer composites were prepared and electromagnetic absorption was evaluated in comparison with those from equiaxed ferrite particles.1) Micaceous <Fe_2> <O_3> particles with average diameters ranging 0.3 to 20 <micro> m were prepared by the flux or hydrothermal method, and they were converted to NiZn or MnZn ferrite under the appropriate conditions with their original shape preserved. Fine NiO and KCl were essential for NiZn ferrite, and a high melting-point flux like <K_2> <SO_4> and <N_2> atmosphere were required for MnZn ferrite. The optimum preparation temperature was 900゜ and 1150゜C for NiZn and MnZn ferrite respectively.2) Ferrite-polymer composites exhibited a wider and lower resonance frequency than those prepared from equiaxed ferrite particles with the same average particle size.