Enhancement of Microwave Absorption Characteristics in Aligned M-type Barium Ferrite Ba_(1-x)La_xZn_xFe_(12-x-y)(Me_(0.5)Mn_(0.5))_yO_(19) (x = 0.0 approx 0.5, Me: Sn, Zr, y = 1.0 approx 3.0) by Metal Substitution

摘要

Microwave radiation in the GHz band is increasingly being used in many various communication devices. However, this has brought about the problems of electromagnetic interference (EMI). Now M-type Ba ferrite is expected to be used as a powerful countermeasure to EMI. Our recent works have shown that M-type Ba ferrite is promising material for microwave absorber in the GHz range. The electromagnetic resonance absorption properties depend on the complex permeability mu = mu' - j mu", particularly the imaginary part mu" = M_S/2H_A alpha (M_S: saturation magnetization, H_A: anisotropy field, a: extinction coefficient). We investigated the effects of substitution composition (x) of Me for Ba (Me: La) and substitution composition (y) of Me ion (Me: Zn, Zr, Sn) for Fe~(3+) on the electromagnetic absorption properties of the Ba_(1-x)La_xZn_xFe_(12-x-y)(Me_(0.5)Mn_(0.5))_yO_(19) compound. The c-axis aligned samples were formed into toroidal shapes. The magnetic properties (M_S, H_A) and the resonance absorption properties (mu_r', mu_r" etc) were measured using a VSM and a network analyzer. The aligned Zr-substituted samples (x = 0.0, y = 1.4) showed values of H_A = 0.21 MAm~(-1), and mu' = 7.5 and mu" = 7.1 that were higher than those of (TiMn) substituted samples~(3)). The matching thickness dm decreased to 0.8mm at the matching frequency of 7.6 GHz. In the sample of x = 0.0 and y = 1.5, mu' = 7.7 and mu" = 6.7 were obtained, and the matching thickness dm was 0.98 mm at 5.95 GHz. Also, Sn-substituted samples showed high m' and m" values of 6.3 and 6.3, respectively, and d_m of 1.02 mm. It is therefore concluded that Sn or Zr substitution is effective in enhancing the electromagnetic wave absorption characteristics of M-type Ba ferrite absorber.