Electromagnetic Wave Absorption Properties of Co-Ti Substituted Ba M-Type Ferrite Produced by a Modified Chemical Coprecipitation

摘要

In this paper, the electromagnetic wave absorption properties of Co-Ti substituted Ba M-type hexagonal ferrite (BaFe_(9.5)(Co_(1-y)Ti_y)_(2.5)O_(19) (y = 0.4 approx 0.8)) produced by a modified coprecipitation method were investigated. This modified chemical coprecipitation method was the combination of the coprecipitation and the synthesis from a salt melt. The sample, Ba_(9.5)(Co_(0.5)Ti_(0.5))_(2.5)O_(19) sintered at 1423 K for 5h, whose powder was produced by the modified coprecipitation method, exhibited high permeability (mu_r"_(max) = 11) and reflection loss (R.L.) around - 10dB at a relatively wide frequency range (0.8 approx 9GHz) comparable to the Ultra Wide Band (UWB). In order to enhance the sintering, the addition of Bi_2O_3 was carried out. The Ba_(9.5)(Co_(0.4)Ti_(0.6))_(2.5)O_(19) sample sintered at 1423 K for 5 h with a Bi_2O_3 content of 2 mass percent, exhibited high permeability (mu_r"_(max) = 25 and mu_r"_(at 1GHz) = 10). This sample also showed good microwave absorption properties (reflection loss: R.L < - 20dB) with a small matching thickness (d_m) of 3.1mm at 0.65 GHz and f centre dot d product (f centre dot d) of 2.0GHz-mm. It can be said that the Ba M-type ferrite produced by the modified coprecipitation method has a possibility to become a material for the thinner microwave absorber in the several GHz range.