| Research Abstract |
Recentry Microwave radiation in the GHz band is increasingly being used in many various communication devices. However, this has brougt about the problem 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 a promising material for microwave absorber in the GHz range. The magnetic resonance absorption properties depend on the complex permeability μ=μ'-jμ" particularly the imaginary part μ"=Ms/2Haα. (Ms : saturation magnetization, Ha : anisotropic field α : extinction coef.) and the complex permissivity ε=ε'-jε". A high complex permeability μ" has been obtained in Ba Fe_<12-x> (Ti_<0.5>Mn_<0.5>)_xO_<27> compound. in which Fe^<3+> was substituted by (Ti_<0.5>Mn_<0.5>). And As hexagonal ferrite exhibits a uniaxial anisotropy, it may be expected that the microwave absorption properties would be enhaned if the sample are aligned using the press in magnetic field. In this
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study we used Mn(II) and Ti, Zr and Sn of Group IV as substitute for Fe^<3*> in BaFe_<12-x> (Me_<0.5>Mn_<0.5>)_xO_<27> : (Me : Ti, Zr, Sn) (x=0-4.0) compound. The sampls were prepared by conventional powder metallurgy method and were formed into toroidal shapes whose c-axis were aligned vertically to the sample thickness. Then we investigated the effects of saturation magnetization Ms and substitution composition (x) of Me for Fe^<3+> by Me ion (Me : Ti.Zr, Sn), on the electromagnetic absorption properties of the Ba Fe_<12-x> (Me_<0.5>Mn_<0.5>)_xO_<27> (Me : Ti, Zr, Sn) compound. The magnetic properties and the resonance absorption characteristics (μ', μ" etc) were measured using a VSM and a network analyzer. The aligned Ti-, Sn- an d Zr- substituted samples showed values of μ"=4.4, 5.1, 5.7 and matching thickness d_m=0.9mm, 0.6mm, 0.4mm, respectively. These μ" values is significantly larger than 3.8 for isotropic (TiMn)-substituted samples. It is therefore concluded thatt the metal ion substitution such as Ti, Sn, Zr and Mn and the c-axis alignment in hexagonal ferrite are effective in enhancing the electromagnetic wave absorption characteristics of M-type ferrite absorber. Less
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