Soft magnetic FeSiBPCu heteroamorphous alloys with high Fe content

Fe–Si–B amorphous alloys with less than $80\text{at}\text{.}\%$ Fe are now in practical use because of their excellent magnetic softness and rather high magnetization $\left({\mathit{J}}_s\right)$ basically owing to the lack of intrinsic magnetic anisotropy and the high Fe content, respectively. A strict upper limit of the Fe content (about $80\text{at}\text{.}\%$ ) for the formation of a single amorphous phase with good magnetic softness hinders the improvement in ${\mathit{J}}_s$ of the Fe-based amorphous alloys. The alloys with the high Fe content exceeding the limit commonly have the as-quenched structure consisting of coarse $\alpha \text{-Fe}$ grains in an amorphous matrix, which inevitably results in inferior magnetic softness. The simultaneous addition of proper amounts of P and Cu is found to be significantly effective in decreasing the grain size of $\alpha \text{-Fe}$ phase, formed in an amorphous matrix in the as-quenched ${\text{Fe}}_{82}{\text{Si}}_9{\text{B}}_9$ amorphous alloys with high Fe content exceeding the limit. Fe-rich ${\text{Fe}}_{81.7}{\text{Si}}_9{\text{B}}_7{\text{P}}_2{\text{Cu}}_{0.3}$ heteroamorphous alloy with an as-quenched structure consisting of extremely small $\alpha \text{-Fe}$ -like clusters of about 3 nm or smaller in diameter, randomly dispersed within the amorphous matrix, exhibits the lower coercivity of $7\text{A}{\text{m}}^{-1}$ and the higher ${\mathit{J}}_{\text{s}}$ of 1.56 T than the typical Fe-based monolithic amorphous alloy at an as-quenched state.