Magnetic pinning effects of epitaxial LaxSr12xMnO3 nanostructured thin films on YBa2Cu3O72d layers

International audienceThe present paper presents the effects of a nanostructured, ferromagnetic La1 xSrxMnO3(LSMO) thin film on the pinning characteristics of an epitaxial YBa2Cu3O7(YBCO) thin film deposited on top. Ordered arrays of LSMO grains were obtained upon growing the film on a terraced (001) SrTiO3 substrate. The analyses of magnetic measurements revealed the presence of a complex vortex pinning mechanism within the YBCO film. With respect to a reference single YBCO layer, an additional pinning potential was observed. Its temperature evolution suggests that a magnetic pinning mechanism is responsible for improved pinning characteristics in the high temperature and field region. Based on the morphology of the underlying LSMO buffer, a strong pinning force is expected to arise due to the anti-dot formations, where a high magnetization gradient exists

Oxygen incorporation effects in annealed epitaxial La(1−x)SrxMnO3 thin films

International audienceThis paper presents our results regarding oxygen incorporation effects in epitaxial La(1-x)SrxMnO3 thin films, deposited on SrTiO3 (001) single crystal substrates, by annealing in different gas mixtures of argon and oxygen. A particular emphasis is placed on the correlation of structural properties with the magnetic properties of the films, Curie temperature, and coercive field. In this sense, we demonstrate that the evolution of the diffuse part of the ω-scans performed on the films are due to oxygen excess in the film lattice, which creates cationic vacancies within the films. Also, we show that two regimes of oxygen incorporation in the films exist, one in which the films evolve toward a single phase and oxygen stoichiometry is recovered, and a second one dominated by oxygen over-doping effects. In order to support our study, XPS measurements were performed, from which we have evaluated the Mn3+/Mn4+ ionic rati

Epitaxial growth and characterization of La2Zr2O 7 multilayers on biaxially textured NiW substrate by chemical solution deposition under highly reducing conditions

The paper presents the growth and characterization of highly textured La2Zr2O7 (LZO) multilayer coatings on Ni-5 at.%W (NiW) biaxially textured substrates by chemical solution deposition (CSD) under highly reducing conditions (Ar + 12%H2) in order to protect the metallic substrate from oxidation. The coating solution consists in a stoichiometric mixture of lanthanum and zirconium acetylacetonates dissolved in an excess of propionic acid. The precursor chemistry was studied by means of infrared spectroscopy, thermogravimetric-differential thermal analyses, Raman spectroscopy and X-ray diffraction carried out on the precursor powder. The as-grown multilayer LZO coating exhibits a sharp in-plane and out-of-plane texture, with the full-width-at-half-maximum of the \u3c9-scans and \u3c6-scans of about 7.2 and 8.0, respectively, close to that of the NiW substrate. The volume fraction of the c-axis oriented grains from the top layer of the coating increases with the number of layers. The LZO coating exhibits a smooth and crack-free surface, appropriate for the further epitaxial growth of a seed layer for the YBa2Cu3O7 - x (YBCO) deposition. Transmission Electron Microscopy was used to investigate the microstructure of the CSD LZO thin films deposited on flexible NiW substrates. A high density of nanovoids, with a size ranging between 10 and 30 nm, was observed in the LZO layers. YBCO films epitaxially grown by pulsed laser deposition on the CSD LZO buffer layer exhibit critical current densities, Jc, close to 1.6 MA/cm2 at 77 K and self-field and zero resistance critical temperature (Tc(R = 0)) of 90.3 K

Mid-infrared spectroscopy of candidate active galactic nuclei-dominated submillimeter galaxies

Spitzer spectroscopy has revealed that sime80% of submm galaxies (SMGs) are starburst (SB)-dominated in the mid-infrared. Here we focus on the remaining sime20% that show signs of harboring powerful active galactic nuclei (AGNs). We have obtained Spitzer-InfraRed Spectrograph spectroscopy of a sample of eight SMGs that are candidates for harboring powerful AGNs on the basis of IRAC color selection (S 8 μm/S 4.5 μm>2, i.e., likely power-law mid-infrared spectral energy distributions). SMGs with an AGN dominating (gsim50%) their mid-infrared emission could represent the "missing link" sources in an evolutionary sequence involving a major merger. First of all, we detect polycyclic aromatic hydrocarbon (PAH) features in all of the SMGs, indicating redshifts from 2.5 to 3.4, demonstrating the power of the mid-infrared to determine redshifts for these optically faint dusty galaxies. Second, we see signs of both star formation (from the PAH features) and AGN activity (from continuum emission) in our sample: 62% of the sample are AGN-dominated in the mid-infrared with a median AGN content of 56%, compared with 1.65 works well at selecting mid-infrared energetically dominant AGNs in SMGs, implying a duty cycle of ~15% if all SMGs go through a subsequent mid-infrared AGN-dominated phase in the proposed evolutionary sequence