A. Lupascu

Tuning magnetic coupling in Sr2IrO4 thin films with epitaxial strain.

We report x-ray resonant magnetic scattering and resonant inelastic x-ray scattering studies of epitaxially strained Sr2IrO4 thin films. The films were grown on SrTiO3 and (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates, under slight tensile and compressive strains, respectively. Although the films develop a magnetic structure reminiscent of bulk Sr2IrO4, the magnetic correlations are extremely anisotropic, with in-plane correlation lengths significantly longer than the out-of-plane correlation lengths. In addition, the compressive (tensile) strain serves to suppress (enhance) the magnetic ordering temperature TN, while raising (lowering) the energy of the zone-boundary magnon. Quantum chemical calculations show that the tuning of magnetic energy scales can be understood in terms of strain-induced changes in bond lengths.

Dilute magnetism and spin-orbital percolation effects in Sr 2 Ir 1− x Rh x O 4

We have used a combination of resonant magnetic x-ray scattering and x-ray absorption spectroscopy to investigate the properties of the doped spin-orbital Mott insulator Sr2Ir1-xRhxO4 (0.07 <= x <= 0.70). We show that Sr2Ir1-xRhxO4 represents a unique model system for the study of dilute magnetism in the presence of strong spin-orbit coupling, and provide evidence of a doping-induced change in magnetic structure and a suppression of magnetic order at x(c) similar to 0.17. We demonstrate that Rh-doping introduces Rh3+/Ir5+ ions which effectively hole-dope this material. We propose that the magnetic phase diagram for this material can be understood in terms of a novel spin-orbital percolation picture.

Structural study of Bi2Sr2CaCu2O8+δ exfoliated nanocrystals

We demonstrate that structural and spectroscopic information can be obtained on exfoliated nanocrystals as thin as 6 nm. This can be achieved by using a combination of micro X-ray fluorescence (μXRF), micro X-ray absorption near-edge spectroscopy (μXANES), and X-ray microdiffraction (μXRD) techniques. Highly focused, tunable X-ray beams available at synchrotron sources enable one to use these non-invasive characterization tools to study exfoliated samples on a variety of substrates. As an example, we focused on exfoliated nanocrystals of the high temperature superconductor Bi2Sr2CaCu2O8+δ. μXRF is used to locate the sample of desired thickness; μXANES and μXRD are used to obtain electronic and structural information, respectively. We find that the “4.7b” structural modulation, characteristic of the bulk crystals, is drastically suppressed for exfoliated crystals thinner than 60 nm.

Dilute Magnetism and Spin-Orbital Percolation Effects in Sr2Ir1 and #8722;xRhxO4

We have used a combination of resonant magnetic x-ray scattering and x-ray absorption spectroscopy to investigate the properties of the doped spin-orbital Mott insulator Sr2Ir1-xRhxO4 (0.07 <= x <= 0.70). We show that Sr2Ir1-xRhxO4 represents a unique model system for the study of dilute magnetism in the presence of strong spin-orbit coupling, and provide evidence of a doping-induced change in magnetic structure and a suppression of magnetic order at x(c) similar to 0.17. We demonstrate that Rh-doping introduces Rh3+/Ir5+ ions which effectively hole-dope this material. We propose that the magnetic phase diagram for this material can be understood in terms of a novel spin-orbital percolation picture.

Dilute Magnetism and Spin-Orbital Percolation Effects in Rh-doped Sr2IrO4

We have used a combination of resonant magnetic x-ray scattering and x-ray absorption spectroscopy to investigate the properties of the doped spin-orbital Mott insulator Sr2Ir1-xRhxO4 (0.07 <= x <= 0.70). We show that Sr2Ir1-xRhxO4 represents a unique model system for the study of dilute magnetism in the presence of strong spin-orbit coupling, and provide evidence of a doping-induced change in magnetic structure and a suppression of magnetic order at x(c) similar to 0.17. We demonstrate that Rh-doping introduces Rh3+/Ir5+ ions which effectively hole-dope this material. We propose that the magnetic phase diagram for this material can be understood in terms of a novel spin-orbital percolation picture.