Ferromagnetic domain structure of iron whiskers with <111> axes

Iron whiskers, with axes in directions and {110} faces separated by {112} faces, have been grown, and the domain patterns present were observed using the powder pattern technique. The structure consists of six main domains magnetized at ±55° to the axis in easy directions. The main walls are 90° walls having a zig-zag structure and meet the whisker surfaces in the {112} faces. These walls are normal zig-zag walls but are here seen obliquely, producing a surface zig-zag angle of 147°. At these faces there is a normal component of magnetization, and complex closure structures form to reduce the resulting magnetostatic energy. Two different types of closure structure are observed and the different patterns appear on alternate main domains. In the {110} faces the magnetization is in the surface so that no closure structure is necessary. The effect of applying magnetic fields perpendicular and parallel to the whisker axis was studied: in the former case the changes occurred by displacement of the junction of the walls, while in the latter, bodily movement of the main walls and growth of new walls in {112} planes appeared to take place. Tension was applied along the whisker axis, and the resultant changes in the domain pattern were caused by the interaction of the applied stress with the two different types of closure structure. At high applied stresses, a sudden change occurred to a complex surface structure with the disappearance of the original zig-zag walls; this pattern remained when the stress was removed.