PHOTOGRAPHS OF DIFFRACTION PATTERN OF FERROMAGNETIC CRBR3

Sharp diffraction patterns of the Fresnel type, which are free from distortion, have been photographed using monochromatic light and fixing the crystal to a 50 μm hole diaphragm cooled to 20 °K in an optical cryostat. Temporary saturation of the magnetization gives three different types of patterns according as the magnetic field forms an angle of 90, 45, or 0° with the crystal c‐axis. Linearly polarized light gives interference spots of the first order polarized perpendicular to the primary light. An interpretation is presented considering also the circular dichroism. Second‐order spots polarized parallel to the primary light are probably due to the domain walls. Above an activation temperature of TA = 31.5 °K the domain walls become mobile. Hereby the 90° and the 45° type change into the 0° type. The latter also appears after cooling from above TC. Copyright © 1969 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim