Nanocrystalline soft magnetic materials

TLDR

Nanocrystalline structures, such as devitrified glassy FeCuNbSiB alloys with 10–15 nm bcc‑FeSi grains, suppress magnetocrystalline anisotropy and magnetostriction, enabling soft magnetic behavior. The hysteresis loop is tuned by inducing uniaxial anisotropy through magnetic‑field annealing. These materials exhibit soft magnetic properties comparable to permalloys or near‑zero‑magnetostrictive Co‑based amorphous alloys, yet with higher saturation induction.

Abstract

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.