Growth and characterization by X-ray topography of highly perfect crystals
Single nickel crystals were grown from the melt by the Czochralski technique. Domain wall movements under applied magnetic fields were observed by using the Lang technique for X-ray topography. Magnetization measurements at room temperature were recorded and the variation of coercivity as a function of temperature was examined. Although low dislocation-density crystals were obtained, dislocation free growth was not achieved, copper single crystals were grown to compare the perfection with that of nickel. The effect of geometrical dimensions of crystal, neck, seed and neck angle on the temperature gradient at the interface of crystal and melt was examined theoretically using the model developed by Buckley-Golder and Humphreys. The model was extended to consider conical crystal and seed. It was found that for nickel the diameter had little effect on the thermal gradient. Increase of crystal cone angle led to a significant decrease in the thermal gradient at the interface. Real time movement of haematite domains under applied magnetic fields has been studied by synchrotron X-ray radiation topography.