2009 Volume 50 Issue 1 Pages 204-209
Technically important nanocrystalline soft magnetic alloys and their derivatives always include metal elements such as Nb, Zr, Mo, etc. and/or Cu to realize the nanostructure, which results in a remarkable decrease of saturation magnetic flux density (Bs) and a significant increase in material cost. With the aim to solve the serious problem, we successfully developed new FeSiBPCu nanocrystalline soft magnetic alloys. The melt-spun Fe83.3–84.3Si4B8P3–4Cu0.7 (at%) alloys have heterogeneous amorphous structures including a large amount of α-Fe clusters, 2–3 nm in size, due to the unusual effect of the simultaneous addition of the proper amounts of P and Cu. The hetero-amorphous alloys exhibit higher Bs of about 1.67 T than the representative amorphous and the nanocrystalline alloys, and the low coercivity (Hc) of 5–10 Am−1. A homogeneous nanocrystalline structure composed of small α-Fe grains with a size of about 10 nm can be realized by crystallizing the hetero-amorphous alloys. The nanocrystalline alloys show extremely high Bs of 1.88–1.94 T almost comparable to the commercial Fe-3.5 mass%Si crystalline soft magnetic alloys, and low Hc of 7–10 Am−1 due to the simultaneous realization of the homogeneous nanocrystalline structure and small magnetostriction of 2–3×10−6. In addition, the alloys have a large economical advantage of lower material cost and better productivity than the ordinary soft magnetic nanocrystalline alloys now in practical use.