Domain investigation on coated unpolished Si-Fe sheets

From domain investigations reported in the literature, it is concluded that the scanning electron microscope (SEM) technique, while revealing the main domain structure in a satisfactory way, gives little information about supplementary domains in the case of commercially coated sheets. It is demonstrated that even more information is attained by means of a technique using a colloid which is destabilized by a special agent. Resulting particle patterns have a tendency to show treelike structures representing surface domains magnetized partly in transverse directions. On slight bending, the formation of trees on one side of the sample gives information about the orientation of individual grains, while disappearance of trees on the other side allows observations of the main domain structure with high contrast. A second technique discussed allows the detection of the main domain width by computerized field scanning. Results are given for modifications of domain widths due to changing demagnetization frequency and due to compressive stress applied normal to the sheet surface, respectively. For both techniques, the application of an external field is not needed.