X-ray and neutron topography observations of domains and dislocations
A brief introduction to the theory of magnetism and magnetic domains is given which is followed by a review of X-ray topography techniques and an outline of the theory and contrast mechanisms necessary for the interpretation of the topographs. Results are presented on the perfection of flux grown rare-earth germanate crystals which clearly indicate the usefulness, to the crystal grower, of synchrotron X-ray topography for rapid routine assessment of a large number of crystals. The techniques of neutron topography are described and some of the more important results obtained are reviewed. Results obtained with neutron topography on the possible correlation between surface vicinal features and dislocations in holmium galium garnet are presented. These results, although not conclusive, provide further evidence of a probable correlation. Previous work reported on the antiferromagnetic KCoF(_3) is described with particular reference to the limited number of domain observations. Previous work on the motion of antiferromagnetic domain walls under an applied magnetic field has been extended by considering the case of the motion of these walls under an applied stress using both synchrotron X-ray topography and rocking curve measurements. The critical stress achieved was in reasonable agreement with that predicted from the magnetic field data. These results also confirm that data obtained in torque magnetometry and linear dichroism experiments may be explained by the motion of antiferromagnetic domain walls under stress. Work on the magnetic properties of terbium is reviewed, particularly work relating to measurements of magnetostriction. An X-ray technique for measuring the magnetostriction of high magnetostriction materials without resorting to absolute lattice parameters is described and the results obtained on using this technique to measure the magnetostriction of terbium are presented. These results are fitted to a two-ion interaction model. Work on the highly magnetostrictive Tb(_.27)Dy(_.73)FE(2) is described and results are presented on the observation of magnetic domains in this material in an applied magnetic field. Calculations of the domain wall energies and widths are presented which enabled the domain structure to be interpreted.