Magnetic domain structures in electrical steel sheets studied by Lorentz microscopy and electron holography

Magnetic domain structures of doubly oriented and non-oriented electrical steel sheets, the former of which has two perpendicular magnetic easy axes in the sheet plane, have been observed by Lorentz microscopy and electron holography. In the demagnetized state, the doubly oriented electrical steel sheet shows straight lines of domain walls with homogeneous distribution of lines of magnetic flux. On the other hand, non-oriented electrical steel shows irregular distribution of domain walls with curved lines of magnetic flux. Through the in situ observation of magnetization process of these electrical steel sheets, it has been found that domain walls in doubly oriented electrical steel sheets move continuously, while domain walls in non-oriented electrical steel sheets move discontinuously. It has been also clarified that the domain walls in non-oriented electrical steel sheets are pinned at the precipitates which are considered to consist of Al₂O₃, SiO₂, MnO and TiO₂. These differences in the movement of domain walls are briefly discussed with their magnetic properties.