Study of magnetic structures induced by bending in (100) Fe–Si single crystals

Abstract

Magnetic domain structures induced by bending (axis of bending along [010]) in (100) Fe–Si single crystals have been investigated by means of the Kerr technique and the Lang method. In the zone of the sample under tension (A), the magnetization is parallel to the surface and the classical 180° wall domain pattern is observed. In part of the zone under compression (B), the easy axis is normal to the surface and two kinds of stray-field-free structures (P and N) similar to the Landau and Lifschitz structure are observed. The magnetic configurations in zones A and B are linked by an inner magnetic structure located near the neutral plane which is a (100) 90° wall and a (100) 180° wall for structures P and N, respectively. An hexagonal pattern is observed on x-ray topographs in the case of both structures P and N. We propose tentatively to relate this pattern to the classical zigzag instability of the 90° walls in the Landau closure domains (structure N), as well as (structure P) to a new kind of instability of the (100) 90° wall, due to the magnetostrictive relaxation of long-range stresses created by such a wall. The energy of each structure is calculated. Theoretical periodicities compare well with the experimental ones. The volume occupied by the structures in zone B increases when the radius of curvature decreases, up to one-half of the sample volume. A critical value of the radius of curvature is computed, above which structure P or N disappears.