Crystallographic and Magneto-Dynamic Characterization of Thin-Film Spintronic Materials

This thesis sets out to identify and characterise the critical properties of two spintronic materials, the half-metallic Fe3O4 and the amorphous rare earth-transition metal alloy GdFe. The critical property of Fe3O4 is its crystal ordering, due to the array of exchange and superexchange interactions which define its conductive and magnetic behaviour. A series of post-oxidized Fe3O4||MgO (001) thin-films have been produced and the oxide growth has been analyzed by high resolution transmission electron microscopy (HRTEM). The quality of the film has been assessed by magnetometry and critical parameters for the growth of quality films are described. Previous procedures on the (001) orientation turn out to have masked much of the disorder in the films. This meant that judgments of quality based on magnetometry conflicted with optic data. By cutting down the (011) plane this research was able to resolve these conflicts and effectively explain the performance of a film as observed from magnetometry data. Previous work has elucidated the theoretical imperfections that can exist in this material. This work confirms the potential for these defects and has identified others. The characteristic visibility criteria for these crystal defects are confirmed and extended. By contrast the critical property of GdFe is the temperature dependent coupling between rare earth and transition metal sublattices. A measurement system was constructed to resolve the temperature dependence of the magneto-optic Kerr effect at femtosecond time scales. By this method, the theoretical timeline of dynamic behaviour has been experimentally validated and enhanced. Observations of resolved sublattice dynamics have been identified and interpreted, including a clear indication of picosecond ferromagnetic ordering. As such this work corroborates and advances existing techniques for the production, analysis and understanding of these spintronic materials.