Fe-Si-B amorphous alloys with less than 80 at. % Fe are now in practical use because of their excellent magnetic softness and rather high magnetization (Js) 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 at. %) for the formation of a single amorphous phase with good magnetic softness hinders the improvement in Js 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 α-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 α-Fe phase, formed in an amorphous matrix in the as-quenched Fe82Si9B 9 amorphous alloys with high Fe content exceeding the limit. Fe-rich Fe81.7Si9B7P2Cu0.3 heteroamorphous alloy with an as-quenched structure consisting of extremely small α-Fe -like clusters of about 3 nm or smaller in diameter, randomly dispersed within the amorphous matrix, exhibits the lower coercivity of 7 A m-1 and the higher Js of 1.56 T than the typical Fe-based monolithic amorphous alloy at an as-quenched state.
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