On magnetic domain configurations in single-crystal, (112)-orientation plates of iron-silicon alloy: some X-ray topographic observations and their interpretation

Possible magnetization states of a cubic ferromagnetic crystal having easy magnetization directions parallel to the cube axes (as in Fe + 3 mass % Si alloy) can be represented using a regular octahedron, as first shown by Néel. This model is developed to derive rules that govern shapes and relative volumes of the differently magnetized domains needed to produce mean magnetization lying in a plane of any orientation. Single-crystal plates of Fe + 3 mass % Si alloy not containing an easy-magnetization direction, such as plates parallel to (112) studied in this work, are in general subdivided into a hierarchy of domains that in spatial scale diminish from specimen interior towards specimen surfaces. X-ray topography offers a non-contacting method of mapping domain configurations. Under appropriate diffraction conditions the strains associated with 90° Bloch walls generate strong diffraction contrast. In X-ray transmission topographs the superimposition of contrast from surface closure domains upon that of inner domains generally gives rise to highly complex images from (112) plates. However, with specimen thicknesses less than 20 μm the patterns can become sufficiently simplified to make possible the identification of shapes and magnetization axes of all domains present. A pattern in this class is illustrated, and interpreted with the aid of the octahedron. Reasonable agreement is found between the observed size scale of the domains and that calculated for minimum energy in the domain structure proposed.