Influence of elastic and plastic strain on the magnetization process in Fe - 3.5 % Si

The analysis of Barkhausen noise amplitude distributions is applied to the study of strain dependence of the magnetization process between 0 and 16 % strain in commercial grain oriented and isotropic Fe- 3.5 % Si sheet. The Barkhausen noise is excited at 4 Hz magnetizing frequency and analysed in the range 300 to 15,000 Hz. The measurements indicate a strong interaction between average noise amplitude and elastic strain, depending on the direction of the magnetizing field. In the plastic region the analysis is carried out with and without simultaneously applied elastic tension. In this case the average noise amplitude appears to follow sensitively the changes in dislocation structure starting from single dislocations to different dislocation arrangements, as shown by detailed transmission electron microscope study. The effects are interpreted in terms of the magnetoelastic interaction between domain wall movements and dislocation stress fields. As a result a rather simple nondestructive means for inspecting the microstructural inhomogeneities in transformer iron is suggested.