105 research outputs found
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 NdCaMnO thin films
Thin films of NdCaMnO manganites with colossal
magnetoresistance (CMR) properties have been synthesized by the Pulsed Laser
Deposition technique on (100)-SrTiO. The lattice parameters of these
manganites and correlatively their CMR properties can be controlled by the
substrate temperature . The maximum CMR effect at 75K, calculated as the
ratio is 10 for a deposition temperature of
degC. Structural studies show that the
NdCaMnO film is single phase, [010]-oriented and has a
pseudocubic symmetry of the perovskite subcell with a=3.77 at room
temperature. We suggest that correlation between lattice parameters, CMR and
substrate temperature 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 NdCaMnO strained thin films
Strained thin films of charge/orbital ordered (CO/OO)
(NCMO) with various thickness have grown on (100)-SrTiO and (100)-LaAlO
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 PrCaMnO strained thin films
We have investigated the magnetic-field-induced phase transition of
charge-ordered (CO) PrCaMnO thin films, deposited onto
(100)-oriented LaAlO and (100)-oriented SrTiO 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 ( 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), ultravioletâvisible (UVâvis) 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. UVâvis 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)
VisibilitĂ© et prĂ©sence de lâimage dans lâespace ecclĂ©sial
Cet ouvrage met au cĆur de son propos une interrogation simple : dans lâorganisation complexe de lâespace de lâĂ©glise mĂ©diĂ©vale, les emplacements choisis pour les images qui ornent les murs et les objets nâoffrent pas toujours la possibilitĂ© de voir celles-ci, dâen dĂ©chiffrer le contenu. Certaines semblent rĂ©servĂ©es Ă des groupes de lâassemblĂ©e stationnant dans des espaces spĂ©cifiques, dâautres ne sont pas visibles depuis les principales zones affectĂ©es aux fidĂšles ou aux clercs, dâautres encore sont situĂ©es trop haut. Le rapport, a priori Ă©vident, entre reprĂ©sentation et visibilitĂ© se trouve donc souvent dĂ©menti, appelant alors une nouvelle notion, celle de prĂ©sence. Analyser la tension existant entre ces trois catĂ©gories â figuration, visibilitĂ© et prĂ©sence â implique une Ă©tude croisĂ©e des Ćuvres figurĂ©es, des monuments et des sources Ă©crites. Les notions de mobilitĂ© et de fixitĂ© permettent Ă©galement de prendre en compte les multiples jeux dâĂ©chelles Ă lâĆuvre dans ce lieu rituel quâest lâĂ©glise, impliquant des objets, des manuscrits, des dispositifs liturgiques, des gestes, des dĂ©placements physiques, dialoguant avec un dĂ©cor appliquĂ© au corps mĂȘme du monument, Ă©pousant lâimmobilitĂ© de lâarchitecture. Les cinq chapitres thĂ©matiques qui organisent ce volume mettent en regard diffĂ©rents cas issus de lâOccident mĂ©diĂ©val et de lâOrient byzantin, selon une chronologie longue (de lâAntiquitĂ© tardive Ă la fin du Moyen Ăge), dans une volontĂ© de dĂ©cloisonner les disciplines et les aires gĂ©ographiques afin de tirer tous les enseignements dâune approche transversale de lâimage mĂ©diĂ©vale
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