A magnetic sheet made of Fe–Si–Al flakes was found to have excellent permeability and electromagnetic-interferences characteristics in a quasimicrowave band. The flakes prepared by attrition were embedded in a polymer with their planes lying parallel to the sheet plane. This sheet exhibits a peculiar dual dispersion in permeability. The Curie temperature of the flakes increases with increasing specific surface area of the flakes. This suggests the composition of the flakes changes to excess Fe by oxidation of Si and Al. This deviation from the Sendust composition brings an increase of a magnetoelastic effect and the dual frequency dispersion seems to be associated with stress caused by attrition. On the basis of these results, flakes with more desirable permeability characteristics were produced from raw powder with less Fe content. Consequently, we could fabricate a magnetic composite that possesses superior noise suppressing effect in a quasi-microwave band.
CoNbZr/ceramics multilayered films, the metal layers of which have sequentially changed anisotropy directions, were investigated. Such newly processed film is called ‘‘composite-anisotropy multilayer film.’’ The effects of this new processing on soft magnetic properties were studied. In the case where the shift angle in the easy magnetization direction between neighboring CoNbZr layers is 45°, a smooth B-H loop with low coercivity was obtained. Furthermore, annealing from 200 to 400 °C resulted in high permeability (μ′) of 1000–1500 and excellent frequency responses of μ′ above 100 MHz in all directions in the plane of the film. These results could be explained in terms of magnetic interactions of the CoNbZr magnetic layers which are in close contact with one another across the intervening ceramics layers. These findings indicate that such composite film has many advantages over conventional uniaxial multilayers in applications to magnetic devices. Since these characteristics are thought to be very significant for microdevices composed of disc-shaped magnetic cores, we fabricated a planar microtransformer composed of circular spiral coils and disk-shaped magnetic cores, 2.4 mm in size, using photolithographic technology. The input–output voltage ratio, VOUT/VIN, was measured in the frequency range of 2–40 MHz and showed a high value of 0.83 at 40 MHz.
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