Bitter Patterns on Single-Crystal Thin Films of Iron and Nickel

Abstract

Basic domain structures of epitaxially grown single crystals of Fe and Ni were investigated by the Bitter pattern technique. Films of these materials were obtained by evaporation onto freshly cleaved MgO single crystals heated to an appropriate temperature in a vacuum of 10⁻⁵mm Hg or less. The nature of the resulting films was examined using reflection electron diffraction. The Bitter patterns were obtained with the metal films on the substrate. From the mode of epitaxy, the structure of the domains and the direction of the moments were determined with respect to the orientation of the substrate. The cleavage surface of the substrate is not perfectly flat, but contains rather large steps as well as tear lines, and these defects are clearly observable in the powder patterns. The relations between such imperfections and the domain patterns are discussed. In addition, the patterns show signs of the existence of matching strain between the metal film and the substrate. The effect of the strain becomes more important as the film thickness decreases, as shown by small intricate domains that are formed. The importance of the 90° wall over the 180° wall in the case of thin films with cubic symmetry is emphasized.