Stress deformations and structural quenching in Sm0.5Ca0.5MnO3 thin films allow a huge decrease of the charge order melting magnetic field

Thin films of Sm0.5Ca0.5MnO3 manganites with charge ordering (CO) properties and colossal magnetoresistance were synthesized by pulsed laser deposition technique on (100)-SrTiO3 and (100)-LaAlO3 substrates. We first compare the structural modifications as function of the substrate and film thickness. Secondly, measuring transport properties in magnetic fields up to 24T, we establish the temperature-field phase diagram describing the stability of the CO state and compare it to bulk material. We show that some structural modification induced by the substrate occurs and that the CO melting magnetic field is greatly reduced. Moreover, with the temperature decrease, no modification of the lattice parameters is observed. We then propose an explanation based on the quenching of the unit cell of the film that adopts the in-plane lattice parameters of the substrate and thus, prevents the complete growth of the CO state at low temperature.Comment: to be published in Journal of Applied Physic

Control of the colossal magnetoresistance by strain effect in Nd0.5_{0.5}Ca0.5_{0.5}MnO3_{3} thin films

Thin films of Nd$_{0.5}$Ca$_{0.5}$MnO$_{3}$ manganites with colossal magnetoresistance (CMR) properties have been synthesized by the Pulsed Laser Deposition technique on (100)-SrTiO$_{3}$. The lattice parameters of these manganites and correlatively their CMR properties can be controlled by the substrate temperature $T_{S}$. The maximum CMR effect at 75K, calculated as the ratio $\rho (H=0T)/\rho (H=7T)$ is 10$^4$ for a deposition temperature of $T_{S}=680$ degC. Structural studies show that the Nd$_{0.5}$Ca$_{0.5}$MnO$_{3}$ film is single phase, [010]-oriented and has a pseudocubic symmetry of the perovskite subcell with a=3.77$\AA$ at room temperature. We suggest that correlation between lattice parameters, CMR and substrate temperature $T_{S}$ result mainly from substrate-induced strains which can weaken the charge-ordered state at low temperature.Comment: 9 pages, 4 figures. To be published in Applied Physics Letter

A radical approach to promote multiferroic coupling in double perovskites

Double perovskites provide a unique opportunity to induce and control multiferroic behaviors in oxide systems. The appealing possibility to design materials with a strong coupling between the magnetization and the polarization fields may be achieved in this family since these magnetic insulators can present structural self-ordering in the appropriate growth conditions. We have studied the functional properties of La2CoMnO6 and Bi2CoMnO6 epitaxial thin films grown by pulsed laser deposition. Cation-ordered La2CoMnO6 films display a magnetic Curie temperature of 250 K while cation-disordered Bi2CoMnO6 films present ferromagnetism up to ~ 800 K. Such high transition temperature for magnetic ordering can be further tuned by varying the strain in the films indicating an important contribution from the structural characteristics of the materials. Our approach might be generalized for other oxide systems. At this end, our results are compared with other multiferroic systems. The roles of various cations, their arrangements and structural effects are further discussed.Comment: 12 pages, 5 fig

Relations between structural distortions and transport properties in Nd0.5_{0.5}Ca0.5_{0.5}MnO3_3 strained thin films

Strained thin films of charge/orbital ordered (CO/OO) $Nd_{0.5}Ca_{0.5}MnO_3$ (NCMO) with various thickness have grown on (100)-SrTiO$_3$ and (100)-LaAlO$_3$ substrates, by using the Pulsed Laser Deposition (PLD) technique. The thickness of the films influences drastically the transport properties. As the thickness decreases, the CO transition increases while at the same time the insulator-to-metal transition temperature decreases under application of a 7T magnetic field. Clear relationships between the structural distortions and the transport properties are established. They are explained on the basis of the elongation and the compression of the Mn-O-Mn and Mn-O bond angles and distances of the \QTR{it}{Pnma} structure, which modify the bandwidth and the Jahn-Teller distortion in these materialsComment: 11 pages, 6 figures. to be published in Journal Physics: Condensed Matte

Stabilization of the cubic phase of HfO2 by Y addition in films grown by metal organic chemical vapor deposition

Addition of yttrium in HfO2 thin films prepared on silicon by metal organic chemical vapor deposition is investigated in a wide compositional range (2.0-99.5 at. %). The cubic structure of HfO2 is stabilized for 6.5 at. %. The permittivity is maximum for yttrium content of 6.5-10 at. %; in this range, the effective permittivity, which results from the contribution of both the cubic phase and silicate phase, is of 22. These films exhibit low leakage current density (5x10(-7) A/cm(2) at -1 V for a 6.4 nm film). The cubic phase is stable upon postdeposition high temperature annealing at 900 degrees C under NH3. (c) 2006 American Institute of Physics

A KRAB/KAP1-miRNA Cascade Regulates Erythropoiesis Through Stage-Specific Control of Mitophagy

During hematopoiesis, lineage- and stage-specific transcription factors work in concert with chromatin modifiers to direct the differentiation of all blood cells. We explored the role of KRAB-containing zinc finger proteins (KRAB-ZFPs) and their cofactor KAP1 in this process. In mice, hematopoietic-restricted deletion of Kap1 resulted in severe hypoproliferative anemia. Kap1-deleted erythroblasts failed to induce mitophagy-associated genes and retained mitochondria. This was due to persistent expression of microRNAs (miRNAs) targeting mitophagy transcripts, itself secondary to a lack of repression by stage-specific KRAB-ZFPs. The KRAB/KAP1-miRNA regulatory cascade is evolutionarily conserved, as it also controls mitophagy during human erythropoiesis. Thus, a multilayered transcription regulatory system is present, in which protein- and RNA-based repressors are superimposed in combinatorial fashion to govern the timely triggering of an important differentiation event

High magnetic field transport measurement of charge-ordered Pr0.5_{0.5}Ca0.5_{0.5}MnO3_3 strained thin films

We have investigated the magnetic-field-induced phase transition of charge-ordered (CO) Pr$_{0.5}$Ca$_{0.5}$MnO$_3$ thin films, deposited onto (100)-oriented LaAlO$_3$ and (100)-oriented SrTiO$_3$ substrates using the pulsed laser deposition technique, by measuring the transport properties with magnetic fields up to 22T. The transition to a metallic state is observed on both substrates by application of a critical magnetic field ($H_C>10T$ at 60K). The value of the field required to destroy the charge-ordered insulating state, lower than the bulk compound, depends on both the substrate and the thickness of the film. The difference of the critical magnetic field between the films and the bulk material is explained by the difference of in-plane parameters at low temperature (below the CO transition). Finally, these results confirm that the robustness of the CO state, depends mainly on the stress induced by the difference in the thermal dilatations between the film and the substrate.Comment: 10 pages, 6 figures. To be published in Phys. Rev.

Morphology and Photoluminescence of HfO2Obtained by Microwave-Hydrothermal

In this letter, we report on the obtention of hafnium oxide (HfO2) nanostructures by the microwave-hydrothermal method. These nanostructures were analyzed by X-ray diffraction (XRD), field-emission gum scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDXS), ultraviolet–visible (UV–vis) spectroscopy, and photoluminescence (PL) measurements. XRD patterns confirmed that this material crystallizes in a monoclinic structure. FEG-SEM and TEM micrographs indicated that the rice-like morphologies were formed due to an increase in the effective collisions between the nanoparticles during the MH processing. The EDXS spectrum was used to verify the chemical compositional of this oxide. UV–vis spectrum revealed that this material have an indirect optical band gap. When excited with 488 nm wavelength at room temperature, the HfO2nanostructures exhibited only one broad PL band with a maximum at around 548 nm (green emission)

Visibilité et présence de l’image dans l’espace ecclésial

Cet ouvrage met au cœur de son propos une interrogation simple : dans l’organisation complexe de l’espace de l’église médiévale, les emplacements choisis pour les images qui ornent les murs et les objets n’offrent pas toujours la possibilité de voir celles-ci, d’en déchiffrer le contenu. Certaines semblent réservées à des groupes de l’assemblée stationnant dans des espaces spécifiques, d’autres ne sont pas visibles depuis les principales zones affectées aux fidèles ou aux clercs, d’autres encore sont situées trop haut. Le rapport, a priori évident, entre représentation et visibilité se trouve donc souvent démenti, appelant alors une nouvelle notion, celle de présence. Analyser la tension existant entre ces trois catégories – figuration, visibilité et présence – implique une étude croisée des œuvres figurées, des monuments et des sources écrites. Les notions de mobilité et de fixité permettent également de prendre en compte les multiples jeux d’échelles à l’œuvre dans ce lieu rituel qu’est l’église, impliquant des objets, des manuscrits, des dispositifs liturgiques, des gestes, des déplacements physiques, dialoguant avec un décor appliqué au corps même du monument, épousant l’immobilité de l’architecture. Les cinq chapitres thématiques qui organisent ce volume mettent en regard différents cas issus de l’Occident médiéval et de l’Orient byzantin, selon une chronologie longue (de l’Antiquité tardive à la fin du Moyen Âge), dans une volonté de décloisonner les disciplines et les aires géographiques afin de tirer tous les enseignements d’une approche transversale de l’image médiévale