Helical and Other Stripe Structures in Single-Crystal Permalloy Platelets

Abstract

Four primary stripe patterns are observed in Permalloy single-crystal platelets with {100} surfaces in different regions of thickness and composition. All four structures involve magnetic moment rotations between easy 〈111〉 axes parallel to {110} planes. The first to appear with increasing thickness (0.3<D<1.0 μm) has 〈100〉 stripes and 〈100〉 net magnetization. The second and third coexist from 0.8–1.4 μm, have fine 〈110〉 and broad 〈100〉 stripes, respectively, and have different magnitudes of net magnetization. Both involve 71° rotations parallel to vertical {110} planes. The fourth (D>0.9 μm) achieves appreciable internal flux closure by forming a helical structure through rotations toward alternate 〈111〉 directions in passing from top to bottom surfaces at any stripe, and through having the planar surface component in alternate stripes perpendicular to the stripes. Models for 180° and 90° walls readily follow from the above scheme in conjunction with applied-field observations.