M-hexaferrites with planar magnetic anisotropy and their application to high-frequency microwave absorbers

Magnetic and microwave absorbing properties have been investigated in the M-type barium ferrites (BaFe/sub 12-2x/A/sub x/Co/sub x/O/sub 19/) with planar magnetic anisotropy. For the tetravalent A ions, Ti/sup 4+/ and Ru/sup 4+/ are chosen and the samples are prepared by a conventional ceramic processing technique. At the substitution ratio with in-plane anisotropy which is estimated from the minimum coercivity, the saturation magnetization of the Ru-Co substituted specimens were about twice as large as those of Ti-Co. This leads to higher magnetic resonance frequency, and thus a large absorption loss (in sintered specimens) and small reflection loss (in rubber composites) are predicted at the higher frequencies in the Ru-Co substituted specimens. High-frequency noise suppressors or anti-reflection absorbers can be proposed for use with M-hexaferrites with planar magnetic anisotropy.