Domain Structure During Magnetization of Grain-Oriented 3% Si–Fe as a Function of Applied Tensile Stress

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Abstract
The longitudinal Kerr effect has been used to observed domain structure during dc and 60‐Hz magnetization in conventional (110) [001] grain oriented 3% Si–Fe as a function of applied tensile stress parallel to the rolling direction. The observed domain processes indicate that the source of the Villari reversal in this material is demagnetizing fields occurring at grain boundaries and at the sheet surface. In grains where the [001] tilted out of the sheet surface, demagnetizing fields were produced when 90° flux closure domains were eliminated by applied tensile stress. During magnetization under applied tensile stress, these demagnetizing fields restabilized the original unstressed closure structure. High speed movies of the magnetization process in grains with perfect plane orientation revealed that although the 180° wall spacing was decreased by applied tensile stress the flux became very nonuniform due to the buildup of grain boundarydemagnetizing fields and the average 180° wall velocity was not decreased. The observed domain processes explain the magnetic properties previously observed in this material under applied tensile stress, e.g., decreased maximum permeability, the appearance of negative magnetostriction and lack of improvement in core loss at stress levels in excess of 500 psi.