Effects of surface coatings on domain structure in grain oriented 3% Si-Fe

The effects of surface insulating coatings on magnetic properties in commercial highly grain oriented Si-Fe sheets are shown on the basis of domain observation using a high voltage SEM. The average 180° wall spacing in grain oriented Si-Fe sheets with the coatings could be expressed semiempirically as a function of tilt of the [001] out of the sheet plane and grain length. Iron loss and 180° wall spacing were slightly reduced by the application of a stress coating. The formation of a forsterite coating resulted in an increase in iron loss and a significant decrease in 180° wall spacing. The observation of dynamic domain patterns showed that the forsterite coating made the induction inhomogeneous among the grains. This would increase the iron loss even though the 180° wall spacing was reduced.