Nanocrystalline soft magnetic materials

Nanocrystalline structures offer a new opportunity for tailoring soft magnetic materials. The most prominent example are devitrified glassy FeCuNbSiB alloys which reveal a homogeneous ultrafine grain structure of bcc-FeSi with grain sizes of typically 10-15 nm and random texture. Owing to the small grain size the local magneto-crystalline anisotropy is randomly averaged out by exchange interaction 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 which minimizes magneto-elastic anisotropies. 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. Like in other soft magnetic material the hysteresis loop can be tailored by uniaxial anisotropies induced by magnetic field annealing.