  Flake-shaped FeSi-based metallic amorphous alloy particles, having an aspect
ratio as high as 175 to 1, were prepared by ball milling gas atomized amorphous
powders of an effective diameter of 20 micrometers. The starting powder had a
saturation magnetic flux density, Bs, of 1.5 T and a coercivity, Hc, of 94 A/m.
The aspect ratio of the flakes, as well as their magnetic properties, were
controlled by milling process parameters, such as duration, speed, and the
type, mass and diameter of the milling balls. To minimize the oxidation of the
charge, the powders were handled in an argon gas-purged glove box, milled in
toluene, and subsequently dried in vacuo. Subsequently, soft magnetodielectric
composites were prepared by suspending and aligning the FeSi-based powders in
paraffin wax or epoxy resin. The composites were then pressed into toroids for
measurements of their high frequency complex permeability by a vector network
analyzer. The influence of the flake aspect ratio and volume loading fraction
on the permeability of the composites were investigated. Results indicate that
the composite permeability increases with the flake aspect ratio. For example,
for a given loading factor of 30 vol.%, the composite permeability at 0.1 GHz
nearly tripled and approached the value of 10 by increasing the aspect ratio of
the FeSi-based inclusions from 1 (spheres) to greater than 175 to 1 (flakes).
