Observation through surface coatings of domain structure in 3% Si-Fe sheet by a high voltage scanning electron microscope

Direct observation of magnetic domains in commercial oriented silicon-iron sheet has recently been made possible even under insulating coatings by use of a high voltage scanning electron microscope(SEM). Detailed description is given of the technique for the domain observation. Also, the effects of coatings on domain structure in slit and sheared oriented silicon-iron sheet are shown on the basis of the observation. Variation of domain structure by shearing was insignificant, depending neither on the kind of coating nor on the sheared width. Stress pattern of about 0.5mm width was observed only at the sheared edge. On both surfaces of slit specimen coated with conventional phosphate, clear stress pattern appeared about 1.5mm away from the slit edge. This indicates that slitting induced transverse tensile stress in the specimen. Width of the stress pattern was 5∼15mm, independent of slitting width. In specimen with silica-phosphate coating, the stress pattern was hardly observable. Domain observation after removing silica-phosphate coating or applying compressive stress and magnetostriction measurement indicate that longitudinal tensile stress of about 0.5kg/mm²given by the silica-phosphate coating cancelled the induced transverse tensile stress, suppressing the generation of [100] and [010] domains.