On the theoretical understanding of nanocrystalline soft magnetic materials

Nanocrystalline structures offer a new opportunity for tailoring soft magnetic materials. The most prominent examples are devitrified glassy FeCuNbSiB alloys, which exhibit a homogeneous ultrafine grain structure of bcc FeSi, with grain sizes of typically 10 to 15 nm and random texture. Due to the small grain size, the local magnetocrystalline anisotropy is randomly averaged out by exchange interactions so that there is only a small anisotropy net effect on the magnetization process. Moreover, the structural phases present lead to low or vanishing saturation magnetostriction. Both the suppressed magnetocrystalline anisotropy and the low magnetostriction provide the basis for the superior soft magnetic properties comparable to those of Permalloys or near-zero magnetostrictive Co-base amorphous alloys, but at a higher saturation induction.