Fabrication and Properties of under 10 μ m Sized Amorphous Powders of High B s Soft Magnetic Alloy for High-Frequency Applications

We report on fabrication and magnetic properties of high B_s-Fe₇₆Si₉B₁₀P₅ and Fe_81.5Si_0.5B_4.5P_11.0Cu_0.5C_2.0 alloy powders by gas atomization. Different atomizing gases such as Ar, N₂, and He were used to understand their effects on cooling rate and powder particle size. We show that the amorphous powders of Fe₇₆Si₉B₁₀P₅ alloy with spherical shape and sizes below 90 μm can be obtained easily with Ar gas. This situation strongly changes for the alloy with higher concentration of Fe, i.e., Fe_81.5Si_0.5B_4.5P_11.0Cu_0.5C_2.0. Only powder particles with sizes below 10 μm were amorphous, when Ar was used as an atomizing gas. He and N₂ gases allow higher cooling rates, and powders with sizes below 20 μm become almost amorphous. In addition, an improvement in the yield of smaller sized powders is noticeable. We made toroidal cores of powders with different sizes by mixing with a polymer resin, and pressing under a pressure of 1.5 GPa. The powder cores were annealed at different temperatures. Effect of structure (amorphous and nanocrystalline), and powder particle sizes on core loss, and initial relative permeability were investigated. Lower core loss with a constant initial relative permeability up to more than 100 MHz can be obtained for the cores made from powders of sizes below 10 μm. The magnetic cores reported in this paper are promising for high-power and high-frequency applications.