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Fe-Si-Al of soft magnetic materials are known as high permeability alloys, and these are used as dust cores. In general, Fe-Si-Al powders, what is called "Sendust", have poor compressibility because of their hardness, therefore it is difficult to increase the packing fraction of their core. We researched the effect of packing fraction on magnetic properties in order to mix the powders which have different mean particle size. In case of mixing the coarse powders and fine powders, it is assumed that fine particles penetrate into the opening gaps which are located in close packing of coarse particles. They are called 6-, 4-and 3-configuration. The sizes of opening gap in close packing are 0.414, 0.225 and 0.154 of coarse particle size, respectively. Fe-9.5Si-5.5Al alloy powders were prepared by gas atomization process. Mean particle size of coarse powders are fixed about 40 μm and fine powders are prepared the size by classifier. Coarse powders and fine powders were mixed to the optional ratio. Relative permeability and core loss up to 1 MHz were measured. Packing fraction of core was improved more than 80 % by optimization of the mixing ratio of fine powders. As a result, relative permeability was increased with the packing fraction.

Recently, soft magnetic metal powders are widely used for electric components such as inductors. These are required further improvement of magnetic properties. Fe-Ni soft magnetic alloys are called "Permalloy" and are known as high magnetic permeability alloys. In particular, "Permalloy B (JIS)", Fe-45~50Ni, is expected for application of inductors because of high saturation magnetic flux density. We researched the effect of Si addition into "Permalloy B" on the magnetic properties in high frequency range. Powders were prepared by gas atomization process and mixed with resin and lubricant, and then compacted into toroidal shape cores. These cores were heat-treated for hardening resin and release of internal stress by compaction. Effective permeability was measured by LCR meter up to 100 MHz and core loss was measured by B-H analyzer up to 5 MHz. As a result, permeability was slightly decreased but core loss was reduced by Si addition. Core loss was also reduced by using finer powders (mean particle diameters are less than 10 μm). Moreover, the permeability increased by the heat treatment of core after compaction. We found the availability of soft magnetic metal powders in high frequency over 3 MHz for using inductors.

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