Assessment of the crystal lattice perfection of rare earth and intermetallic single crystals by x-ray topography

Abstract

Single crystals of a number of rare earths and intermetallics used for bulk magnetic measurements have been examined by X-ray diffraction topography using the Bragg geometry. Experiments were performed using both a conventional X-ray source and synchrotron radiation. Tb grown by solid state electrotransport (SSE) from high purity start material had the highest perfection as well as the highest residual resistance ratio. SSE refined Dy was of somewhat inferior perfection while Ho crystals cut from an ingot not SSE processed were of very much poorer quality. The reduction in lattice strain as cutting damage was removed was monitored. A significant decrease in perfection of the Tb was noted over several months following thermal cycling through the Curie temperature. Increase in surface strains due to oxidation was most marked in Gd and the Gd-Tb alloys. In contrast no polishing problems occurred with RAl 2 crystals grown by the Czochralski method. Clean images, showing little long range strain, were obtained from TbAl 2, NdAl 2 and GdAl 2.