New approach to the study of the magnetic permeability aftereffect of amorphous ferromagnetic alloys

A new approach is proposed to study the aftereffect of the magnetic permeability of ferromagnetic metallic glasses. The physical basis of the aftereffect is shown to be the magnetostrictive coupling between structural defects of the amorphous matrix and the saturation magnetization. The structural defects are atomic clusters characterized by the presence of large, correlated fluctuations of the atomic stress tensor $\sigma$, which is a random quantity in the material. A theory based on these assumptions is developed. The permeability aftereffect is predicted to be proportional to product ${\lambda }_s^2〈{\tau }^2〉$ where ${\lambda }_s$ is the saturation magnetostriction, and $〈{\tau }^2〉$ is the second moment of the shear-stress fluctuation. Results of experiments performed to check this prediction in different materials are presented and discussed. The experimental data confirm the validity of the present model.