Structural phases driven by oxygen vacancies at the La0.7Sr0.3MnO3/SrTiO3 hetero-interface

An oxygen vacancy driven structural response at the epitaxial interface between La0.7Sr0.3MnO3 films and SrTiO3 substrates is reported. A combined scanning transmission electron microscopy and electron energy loss spectroscopy study reveal the presence of an elongated out-of-plane lattice parameter, coupled to oxygen vacancies and reduced manganese oxidation state at the La0.7Sr0.3MnO3 side of the interface. Density functional theory calculations support that the measured interface structure is a disordered oxygen deficient brownmillerite structure. The effect of oxygen vacancy mobility is assessed, revealing an ordering of the vacancies with time

Magnetization reversal mechanism in La0.67Sr0.33MnO3 thin films on NdGaO3 substrates

The field angle dependence of the coercive field of La0.67Sr0.33MnO3 thin films grown epitaxially on NdGaO3 substrates with different crystallographic orientations was determined. All films show uniaxial anisotropy. The angle dependence of the coercivity is best described by a two-phase model, explaining the strong increase in the coercive field for increasing field angles, away from the easy axis direction, as well as the sharp decrease for angles close to the hard direction. This implies that magnetization reversal starts with the depinning of domain walls, analogous to the Kondorsky model. With increasing field the reversal in the domains is not abrupt, but is determined by the gradual displacement of the domain walls. These results are of significance for understanding and possibly engineering of the switching behavior of magnetic tunnel junctions

Phonon anharmonicities and ultrafast dynamics in epitaxial Sb2Te3

In this study we report on the investigation of epitaxially grown Sb2Te3 by employing Fourier-Transform transmission Spectroscopy (FTS) with laser-induced Coherent Synchrotron Radiation (CSR) in the Terahertz (THz) spectral range. Static spectra in the range between 20 and 120 cm−1 highlight a peculiar softening of an in-plane IR-active phonon mode upon temperature decrease, as opposed to all Raman active modes which instead show a hardening upon temperature decrease in the same energy range. The phonon mode softening is found to be accompanied by an increase of free carrier concentration. A strong coupling of the two systems (free carriers and phonons) is observed and further evidenced by exciting the same phonon mode at 62 cm−1 within an ultrafast pump-probe scheme employing a femtosecond laser as pump and a CSR single cycle THz pulse as probe. Separation of the free carrier contribution and the phonon resonance in the investigated THz range reveals that, both damping of the phonon mode and relaxation of hot carriers in the time domain happen on the same time scale of 5 ps. This relaxation is about a factor of 10 slower than expected from the Lorentz time-bandwidth limit. The results are discussed in the framework of phonon scattering at thermal and laser induced transient free carriers

Response of the benthic food web to short- and long-term nutrient 1 enrichment in saltmarsh mudflats

Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Marine Ecology Progress Series 474 (2013): 27-41, doi:10.3354/meps10090.We examined the responses of biota at or near the base of the benthic food web to nutrient enrichment in salt marsh mudflats in Plum Island estuary (Massachusetts, USA). To simulate eutrophication, nitrate and phosphate loading rates were increased 10- to 15-fold in creeks fertilized for 2 mo (i.e. short-term enrichment) or 6 yr (chronic enrichment). We found that benthic invertebrate community structure was not altered by nutrient enrichment, although the abundance of epifaunal, but not infaunal, grazers increased. Short-term enrichment had no effect on the food web, but significant changes were detected with chronic enrichment. Grazing experiments with 15N-enriched bacteria and 13C-enriched benthic algae revealed higher per capita ingestion rates of benthic microalgae by nematodes, copepods and hydrobiid snails in the creek with chronic nutrient enrichment where isotope composition also indicated that algae increased in dietary importance. The fraction of bacterial biomass grazed was not affected by nutrient enrichment; however, the fraction of benthic algal biomass grazed increased by 235% with chronic enrichment. This higher grazing pressure was partly the result of dietary changes (increases in per capita feeding rate or a change in selection) but was mostly due to an increased abundance of the grazing consumer with the highest biomass, the snail Nassarius obsoletus. This increased top-down control partially masked the bottom-up effects of nutrient enrichment on algal biomass and helps explain the slow and inconsistent response of microalgal biomass to chronic nutrient enrichment previously observed in this estuary. Our research shows that eutrophication may subtly affect benthic food webs before large, sustained increases in algal biomass are observed.Pierre-Yves Pascal conducted this research while being supported by a 563 postdoctoral fellowship funded by the Department of Energy Office of Biological and 564 Environmental Research Award DE-FG02-05ER64070 and the Louisiana State University 565 College of Science. This material is based upon work supported by the National Science 566 Foundation under Grant Nos. 0213767 and 9726921

Rotation of the magnetic easy axis in La0.67Sr0.33MnO3 thin film on NdGaO3(112)

The in-plane magnetic anisotropy is studied for pseudocubic {011}pc oriented La0.67Sr0.33MnO3 (LSMO) thin film grown on orthorhombic NdGaO3(NGO)(112)o (the subindices “pc” and “o” indicate the pseudocubic and orthorhombic lattice structure, respectively). The direction of the in-plane remanent magnetization of LSMO thin films with different thicknesses is determined. With increasing film thickness the easy axes rotate and the anisotropy changes from uniaxial to biaxial. This is associated with the increasing symmetry of the LSMO with increasing thickness, starting with a monoclinic LSMO structure at the nonrectangular NGO(112)o surface unit cell of the substrate, developing into an orthorhombic structure at the top part of the thickest films

Optimized fabrication of high quality La0.67Sr0.33MnO3 thin films considering all essential characteristics

In this article, an overview of the fabrication and properties of high quality La0.67Sr0.33MnO3 (LSMO) thin films is given. A high quality LSMO film combines a smooth surface morphology with a large magnetization and a small residual resistivity, while avoiding precipitates and surface segregation. In literature, typically only a few of these issues are adressed. We therefore present a thorough characterization of our films, which were grown by pulsed laser deposition. The films were characterized with reflection high energy electron diffraction, atomic force microscopy, x-ray diffraction, magnetization and transport measurements, x-ray photoelectron spectroscopy and scanning transmission electron microscopy. The films have a saturation magnetization of 4.0 {\mu}B/Mn, a Curie temperature of 350 K and a residual resistivity of 60 {\mu}{\Omega}cm. These results indicate that high quality films, combining both large magnetization and small residual resistivity, were realized. A comparison between different samples presented in literature shows that focussing on a single property is insufficient for the optimization of the deposition process. For high quality films, all properties have to be adressed. For LSMO devices, the thin film quality is crucial for the device performance. Therefore, this research is important for the application of LSMO in devices.Comment: Accepted for publication in Journal of Physics D - Applied Physic