Domain Structure of Perminvar Having a Rectangular Hysteresis Loop

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Abstract
An investigation has been made of the magnetic domain structure of Perminvar (43 percent Ni, 34 percent Fe, 23 percent Co) ring specimens having rectangular hysteresis loops after heat-treatment in a magnetic field. Domain patterns obtained with colloidal magnetite showed curved domain boundaries extending completely around the rings, forming circles concentric with them. Changes in magnetization occur when an applied field causes the circular boundaries either to expand or contract so that there is a change in the relative values of clockwise and counter-clockwise flux. A nucleus of reversed magnetization was formed by making a small notch in a specimen, and this decreased the coercive force and hysteresis loss by a factor of two. It was found that in a 180° domain boundary it was possible to make the change in spin orientations, which occurs in going from one side of the boundary to the other, have either a right- or left-hand screw relation, by the application of a field of appropriate sign perpendicular to the surface. The effect of super-posing an applied alternating field was also investigated, and an effective permeability of 4,000,000 was obtained.