Distortion of an FeSi Single Crystal and X‐Ray Topographic Contrast Due to a 90° Ferromagnetic Domain Wall

A crystal lattice distortion due to a plane‐shaped 90° wall between ferromagnetic domains has been found. This distortion is characterized by a matrix Δ P from which the parameter δ(Δθ), corresponding to the variation of the departure from the Bragg condition of the incident X‐ray wave, can easily be calculated for any diffracting plane. The matrix Δ P has been calculated for the (110) and (111) walls, but the calculation can be performed for any magnetically allowed 90° wall. Some qualitative conclusions about the contrast on a 90° wall have been made. The results can be used for further contrast calculations on X‐ray topographs using the dynamical theory of diffraction.