Fabrication and properties of microforged ferromagnetic nanoflakes

Ferromagnetic nanoflakes (quasi-oblate spheroids of soft ferromagnetic alloys with submicron thicknesses and aspect ratios of 10-100) can be processed by microforging micron scale powders in a ball mill. Nanoflakes are potentially useful in fabricating microwave effective media, but the magnetic properties of microforged ferromagnetic flakes have not been previously studied. In this study, we produced ferromagnetic nanoflakes from gas atomized powders of several types of Fe, and alloy powders of FeSi and NiFe. SEM micrographs and sieving fractions show that nanoflakes can be made with thicknesses ~0.4 μm, and that more than 95% of the initial powder mass can be converted into nanoflakes with aspect ratios greater than 50. Magnetic measurements show that composites of planar nanoflakes have magnetic remanences ~25% M_s, μ´s that correlate with the aspect ratio (to values >50), and eddy currents suppressed to frequencies >200 MHz