Magnetic and Structural Properties of Iridates and Cuprates in Reduced Dimensions

Physics at reduced dimensionality has seen an increased interest in the last decade, due to the novel properties that arise in low-dimensional materials. In this dissertation, we have employed scattering and absorption x-ray techniques to investigate the magnetic and structural properties of two classes of transition metal-oxides with reduced dimensionality: Sr2IrO4 (a 5d layered perovskite iridate) and Ba2IrO 4 (a 3d cuprate).;X-ray Resonant Magnetic Scattering (XRMS) was used to study the magnetic properties of epitaxially-strained Sr2IrO4 thin films grown via pulsed laser deposition. Epitaxial strain proves to be a great way of tuning the magnetic transition temperature TN of Sr2IrO4, a system in which the interplay between the strong spin-orbit coupling and crystal field renders the magnetic properties very sensitive to small structural distortion. The strong magneto-elastic coupling in Sr2IrO4 is also illustrated by the observation of a spontaneous magnetostriction effect in a 20-nm thin film sample, which increases significantly at the onset of magnetic ordering, and could be attributed to the strong spin-orbit interactions in the 5d oxide. The 20-nm film also exhibits a smoothly evolving field-driven phase transition, which is irreversible at 5 K. Finally, the XRMS study of a Sr2IrO 4 single-crystal under an applied magnetic field displays a rich field-driven phase diagram, characterized by magnetic domain re-population, a hysteresis behaviour, and a change in magnetic domain size with temperature.;A combination of Micro-Fluorescence (muXRF) and Micro-Diffraction (muXRD) was developed to study the structural properties of nanocrystals obtained via mechanical exfoliation. The structural studies have focused on the thickness dependence of the "4.7 b" structural modulation in Bi2Sr 2CaCu2O8+delta nanocrystals, exfoliated on Si/SiO 2 and mica substrates. The structural modulation is present even at a thickness of 6 nm for Bi2Sr2CaCu2O 8+delta nanocrystals on Si/SiO2, and maintains the same periodicity of "4.7 b". A twofold suppression of the modulation intensity was observed upon reducing the sample thickness from 200 to 6 nm.;All the experimental techniques mentioned above offer insights into the study of thin films and reveal the importance of the substrate-thin film interaction, which can occur both in thin films made by deposition and in exfoliated nanocrystals.