New Fe-B-P-Cu nanocrystalline soft magnetic alloys with high J_s combined with low coercivity H_c

Fe-Si-B amorphous alloys with less than 80 at% Fe are now in practical use due to their excellent magnetic softness (low coercivity H_c) combined with rather high saturation magnetic polarization (J_s) which basically owing to the lack of intrinsic magnetic anisotropy and the high Fe content, respectively. In order to obtain high J_s, high Fe content is required. However, alloys with high Fe content exceeding the limit usually have the as-quenched structure consisting of coarse α-Fe grains in the amorphous matrix, which results in inferior magnetic softness. We have developed a new Fe_85.2B₁₀P₄Cu_0.8 nanocrystalline soft magnetic alloy ribbon (with 5 mm in width and about 20 μm in thickness) made from industrial raw materials in air atmosphere. The as-quenched structure of Fe_85.2B₁₀P₄Cu _0.8 alloy has heterogeneous amorphous structure (a large amount of extremely small α-Fe clusters in addition to amorphous phase). Homogeneous nanocrystalline structure composed of α-Fe grains with a size ∼19 nm was realized by crystallizing the hetero-amorphous alloy. The nanocrystalline alloy exhibit high J_s ∼ 1.83 T (comparable to the commercial Fe-3.5 mass% Si steel) and extremely low H_c ∼ 6.0 A/m. Additionally the alloy has a large economical and industrial advantage of lower material cost and good reproductivity, which has a high potential for the power applications.