Extending the operational frequency range of high B_s – FeSiBP amorphous alloy to GHz by coating the powder surface with silicon oxide

We report on the fabrication, and magnetic properties of high saturation magnetic flux density (B_s) Fe₇₆Si₉B₁₀P₅ glassy alloy powder cores in which powder particles were electrically insulated by a thin layer of silicon oxide. Glassy Fe₇₆Si₉B₁₀P₅ alloy powders produced by the gas atomization technique were treated with silane coupling agent, which forms a thin silicone oxide layer on the powder surface. Toroidal shaped cores were prepared by spark plasma sintering (SPS) technique. Magnetization measurements revealed a slight decrease in the saturation magnetization from 164 emu/g (as prepared powders) to 161 emu/g after surface coating. We show that the powder surface coating is effective for decreasing the core loss at higher frequencies by suppressing the interparticle eddy currents. It is possible to have a high constant initial permeability (μ_i) of ~28 up to ~1.5 GHz by mixing with a small amount of resin. The constant permeability range can be extended to more than 3 GHz by completely insulating the powders electrically. Our results suggest that the metallic powder cores, which have the advantage of operating at higher B_s compared to ferrites can be used in the GHz frequency range by decreasing the powder particle size and electrically insulating the powders by coating their surface properly.