Formation of ultra-fine amorphous powders in (Fe, Co, Ni)-B systems by chemical reduction method and their thermal and magnetic properties

Amorphous ultra-fine powders in (Fe, Co or Ni)-B, Fe-Co-B, Fe-Ni-B and Co-Ni-B systems were produced by reduction of metal ions in an aqueous solution by use of KBH₄. The powders have a spherical shape with diameters ranging from 5 to 20 nm. The boron concentration is in the range of 28 to 37 at% and the composition of metal elements can be controlled by changing the concentration of metal ions. Crystallization temperatures (T_x) and heats of crystallization for the (Fe-Ni)₇₂B₂₈ powders agree with those obtained for the amorphous alloys of the same composition produced by melt spinning. Furthermore, the compositional dependences of T_x, coercivity and magnetization are very similar to those obtained in the chemically synthesized (Fe-Co)₆₃B₃₇, (Fe-Ni)₇₂B₂₈ and (Co-Ni)₆₇B₃₃ amorphous powders and melt-spun (Fe-Co)₇₈Si₈B₁₄, (Fe-Ni)₇₈Si₈B₁₄ and (Co-Ni)₇₈Si₈B₁₄ amorphous ribbons. It is concluded that there is no significant difference in the amorphous structure obtained in the chemically synthesized powders and the melt-spun ribbons, in spite of an essential difference in the formation mechanism of these amorphous alloys.