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X‐ray diffraction on a crystal containing a misfit boundary is solved using dynamical theory (plane wave approximation, Laue case of diffraction). Resulting explicit formulas for complex amplitudes of all diffracted and forward diffracted waves may be used for direct calculation of diffracted and transmitted intensities and of contrast in diffraction topographs.

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The contrast of ferromagnetic domains in (001) Fe-304 Si single crystal plates is studied using X-ray diffraction topography. This contrast is found to be due solely to the difference in deformation on opposite sides of the wall which is produced by magnetostriction. 180' walls are therefore never visible, whereas 90' walls show contrast if diffracting planes not belonging to the zone m,nil are used (m, and m, are unit vectors parallel t o the magnetization on the two sides of the wall). Der Kontrast von ferromagnetischen Domiinen in (001) F e 3 % Si Einkristallpliittchen wird mit der rontgentopographischen Methode untersucht. Der Kontrast hiingt einzig von dem durch Magnetostriktion eneugten Deformationsunterschied auf beiden Seiten der Wand ab. 180O-Wiinde sind deswegen immer unsichtbar, wiihrend 90O-Wiinde nur d a m einen Kontrast aufmeisen, wenn die benutzten Streuungsebenen nicht zur Zone m, -mi1 gehoren (m, und m, sind Einheitavektoren in Richtung der Magnetisierungen auf beiden Seiten der Wand).

Fringe patterns in X‐ray topographic images of 90° ferromagnetic domain walls in Fe–3 wt% Si single crystal specimens prepared as plates parallel to (001) have been investigated with a wide variation of experimental conditions including changes of specimen thickness (in the range 75 to 340 μm), Bragg reflecting plane, order of reflection and X‐ray wavelength (AgKα, MoKα, and CoKα). It is demonstrated that the fringes are dominantly images of real internal fine structure of the 90° walls rather than an X‐ray interference effect, i.e. fault surface fringes. The fringe pattern results from the walls having a zig‐zag structure: walls of mean orientation (110) being composed of facets roughly parallel to (111) and (111). X‐ray topographs enable the mean orientation of the walls to be measured (it may depart by up to 10° from (110)), and the zig‐zag period to be determined (mean value 13 μm) at points within the crystal.

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