Dopant-dependent impact of Mn-site doping on the critical-state manganites: R0.6Sr0.4MnO3 (R=La, Nd, Sm, and Gd)

Versatile features of impurity doping effects on perovskite manganites, $R_{0.6}$Sr$_{0.4}$MnO$_{3}$, have been investigated with varying the doing species as well as the $R$-dependent one-electron bandwidth. In ferromagnetic-metallic manganites ($R$=La, Nd, and Sm), a few percent of Fe substitution dramatically decreases the ferromagnetic transition temperature, leading to a spin glass insulating state with short-range charge-orbital correlation. For each $R$ species, the phase diagram as a function of Fe concentration is closely similar to that for $R_{0.6}$Sr$_{0.4}$MnO$_{3}$ obtained by decreasing the ionic radius of $R$ site, indicating that Fe doping in the phase-competing region weakens the ferromagnetic double-exchange interaction, relatively to the charge-orbital ordering instability. We have also found a contrastive impact of Cr (or Ru) doping on a spin-glass insulating manganite ($R$=Gd). There, the impurity-induced ferromagnetic magnetization is observed at low temperatures as a consequence of the collapse of the inherent short-range charge-orbital ordering, while Fe doping plays only a minor role. The observed opposite nature of impurity doping may be attributed to the difference in magnitude of the antiferromagnetic interaction between the doped ions.Comment: 7 pages, 6 figure

Local Ferromagnetism in Microporous Carbon with the Structural Regularity of Zeolite Y

Magnetization M(H,T) measurements have been performed on microporous carbon (MC) with a three-dimensional nano-array structure corresponding to that of a zeolite Y supercage. The obtained results unambiguously demonstrate the occurrence of high-temperature ferromagnetism in MC, probably originating from a topological disorder associated with curved graphene sheets. The results provide evidence that the ferromagnetic behavior of MC is governed by isolated clusters in a broad temperature range, and suggest the occurrence of percolative-type transition with the temperature lowering. A comparative analysis of the results obtained on MC and related materials is given.Comment: To be published in Physical Review B (2003

Proximity induced metal/insulator transition in YBa2Cu3O7/La2/3Ca1/3MnO3Y Ba_2 Cu_3 O_7 / La_{2/3} Ca_{1/3} Mn O_3 superlattices

The far-infrared dielectric response of superlattices (SL) composed of superconducting YBa$_{2}$Cu$_{3}$O$_{7}$ (YBCO) and ferromagnetic La$_{0.67}$% Ca$_{0.33}$MnO$_{3}$ (LCMO) has been investigated by ellipsometry. A drastic decrease of the free carrier response is observed which involves an unusually large length scale of d$^{crit}\approx$20 nm in YBCO and d$^{crit}\approx$10 nm in LCMO. A corresponding suppression of metallicity is not observed in SLs where LCMO is replaced by the paramagnetic metal LaNiO$_{3}$. Our data suggest that either a long range charge transfer from the YBCO to the LCMO layers or alternatively a strong coupling of the charge carriers to the different and competitive kind of magnetic correlations in the LCMO and YBCO layers are at the heart of the observed metal/insulator transition. The low free carrier response observed in the far-infrared dielectric response of the magnetic superconductor RuSr$_{2}$GdCu$_{2}$O$_{8}$ is possibly related to this effect

Long range electronic phase separation in CaFe3O5

Electronic phase separation is an important feature of many correlated perovskite compounds but hasn’t been seen in other complex oxides with similar physical behaviour such as magnetite. Hong et al. find phase separation between a magnetite-like charge ordered phase and a charge averaged phase in CaFe3O5

Cell-specific expression of runt-related transcription factor 2 contributes to pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease with limited therapeutic options and unknown etiology. IPF is characterized by epithelial cell injury, impaired cellular crosstalk between epithelial cells and fibroblasts, and the formation of fibroblast foci with increased extracellular matrix deposition (ECM). We investigated the role of runt-related transcription factor 2 (RUNX2), a master regulator of bone development that has been linked to profibrotic signaling. RUNX2 expression was up-regulated in lung homogenates from patients with IPF and in experimental bleomycin-induced lung fibrosis. The RUNX2 level correlated with disease severity as measured by decreased diffusing capacity and increased levels of the IPF biomarker, matrix metalloproteinase 7. Nuclear RUNX2 was observed in prosurfactant protein C-positive hyperplastic epithelial cells and was rarely found in myofibroblasts. We discovered an up-regulation of RUNX2 in fibrotic alveolar epithelial type II (ATII) cells as well as an increase of RUNX2-negative fibroblasts in experimental and human pulmonary fibrosis. Functionally, small interfering RNA-mediated RUNX2 knockdown decreased profibrotic ATII cell function, such as proliferation and migration, whereas fibroblasts displayed activation markers and increased ECM expression after RUNX2 knockdown. This study reveals that RUNX2 is differentially expressed in ATII cells vs. fibroblasts in lung fibrosis, which contributes to profibrotic cell function. Cell-specific targeting of RUNX2 pathways may represent a therapeutic approach for IPF

Energies of the delayed neutrons from U²³⁵ fission products /

Manhattan District Declassified CodeIncludes bibliographical references.Mode of access: Internet

High-order parametric generation of coherent XUV radiation

International audienceExtreme ultraviolet (XUV) radiation finds numerous applications in spectroscopy. When the XUV light is generated via high-order harmonic generation (HHG), it may be produced in the form of attosecond pulses, allowing access to unprecedented ultrafast phenomena. However, the HHG efficiency remains limited. Here we present an observation of a new regime of coherent XUV emission which has a potential to provide higher XUV intensity, vital for applications. We explain the process by high-order parametric generation, involving the combined emission of THz and XUV photons, where the phase matching is very robust against ionization. This introduces a way to use higher-energy driving pulses, thus generating more XUV photons