Fabrication of Fe–Si–B based amorphous powder cores by cold pressing and their magnetic properties

Toroid-shaped Fe-base amorphous powder cores were prepared from Fe–Si–B amorphous powder by gas atomization and subsequent cold pressing using organic and inorganic binders, respectively. The characteristics of gas-atomized Fe–Si–B amorphous powder and high-frequency magnetic properties of the cores were investigated. Fe–Si–B amorphous powder, exhibiting good soft magnetic properties with a saturation magnetization of 125 emu/g and a coercivity of 0.4 Oe, were successfully produced by gas atomization in the particle size range below 75 μm. The Fe–Si–B amorphous powder cores using phenol resin as a binder exhibit stable permeability in the high-frequency range up to 10 MHz, showing excellent high-frequency characteristics and superior dc-bias properties with a “percent permeability” of more than 97% at H = 50 Oe. Uniform insulation by phenol resin and good soft magnetic properties of gas-atomized Fe–Si–B amorphous powder lead to the excellent high-frequency characteristics of the cores. Permalloy powder used as a metallic binder enables the fabrication of Fe–Si–B amorphous powder cores by cold pressing. Permalloy powder increases the permeability of the cores, but deteriorates the high-frequency dependence of the permeability at high content.