Preparation of acicular fine particle of Fe-Co alloy and its magnetic characteristics

Acicular fine particles of Fe–Co alloy were prepared by reducing hydrogen of α FeOOH and were coated with Co ferrite precipitate. Co ferrite precipitate was prepared by means of mixing the solution of Fe(NO 3 ) 3 and Co(NO 3 ) 2 whose molecular ratio was 2:1 and the alkaline (pH 11 to 13) solution suspended α FeOOH particles. The amount of the precipitated Co ferrite was 75% of αFeOOH. The saturation magnetization (σ s ) and coercive force ( H c ) of the obtained Fe–Co particles increase with increasing Co concentration. The rate of increase of σ s was about 2 emu/g per at.% of Co, which is twice as large as that of the bulk. It was concluded that the large σ s was caused by the thickness of the oxide layer which covered the Fe–Co particle. The magnetic anisotropy of the Fe–Co particle was considered to be due to shape anisotoropy, because the rates of increase of H c and σ s are almost the equal.