Synthesis of SmFeAsO by an Easy and Versatile Route and its Physical Property Characterization

We report synthesis, structure, electrical transport and heat capacity of SmFeAsO. The title compound is synthesized by one-step encapsulation of stoichiometric FeAs, Sm, and Sm2O3 in an evacuated (10-5 Torr) quartz tube by prolong (72 hours) annealing at 1100oC. The as synthesized compound is crystallized in tetragonal structure with P4/nmm space group having lattice parameters a = 3.93726(33) A and c = 8.49802(07) A. The resistance (R-T) measurements on the compound exhibited ground state spin-density-wave (SDW)-like metallic steps below 140 K. Heat capacity CP(T) measurements on the title compound, showed an anomaly at around 140 K, which is reminiscent of the SDW ordering of the compound. At lower temperatures the CP(T) shows a clear peak at around 4.5 K. At lower temperature below 20 K, Cp(T) is also measured under an applied field of 7 Tesla. It is concluded that the CP(T) peak at 4.5 K is due to the anti-ferromagnetic(AFM) ordering of Sm3+ spins. These results are in confirmation with ordering of Sm in Sm2-xCexCuO4.Comment: 9 pages Text + Figs Contact Author ([email protected]

Superconductivity in SmFe1−xCoxAsO (x = 0.0–0.30)

We report synthesis, structural details, and magnetization of SmFe1−xCoxAsO with x ranging from 0.0 to 0.30. It is found that Co substitutes fully at Fe site in SmFeAsO in an isostructural lattice with slightly compressed cell. The parent compound exhibited known as the spin density wave (SDW) character is below at around 140 K. Successive doping of Co at Fe site suppressed the SDW transition for x = 0.05 and later induced superconductivity for x = 0.10, 0.15, and 0.20, respectively, at 14, 15.5, and 9 K. The lower critical field as seen from magnetization measurements is below 200 Oe. The appearance of bulk superconductivity is established by wide open isothermal magnetization M(H) loops. Superconductivity is not observed for higher content of Co, i.e., x ≥ 0.30. Clearly the Co substitution at Fe site in SmFe1−xCoxAsO diminishes the Fe SDW character, introduces bulk superconductivity for x between 0.10 and 0.20 and finally becomes nonsuperconducting for x above 0.20. The Fe2+ site Co3+ substitution injects mobile electrons to the system and superconductivity appears; however direct substitution introduces simultaneous disorder in superconducting FeAs layer and thus superconductivity disappears for higher content of Co

Superconductivity in SmFe1-xCoxAsO (x = 0.0 to 0.30)

We report synthesis, structural details and magnetization of SmFe1-xCoxAsO with x ranging from 0.0 to 0.30. It is found that Co substitutes fully at Fe site in SmFeAsO in an iso-structural lattice with slightly compressed cell. The parent compound exhibited known spin density wave (SDW) character below at around 140 K. Successive doping of Co at Fe site suppressed the SDW transition for x = 0.05 and later induced superconductivity for x = 0.10, 0.15 and 0.20 respectively at 14, 15.5 and 9K. The lower critical field as seen from magnetization measurements is below 200Oe. The appearance of bulk superconductivity is established by wide open isothermal magnetization M(H) loops. Superconductivity is not observed for higher content of Co i.e. x = 0.30. Clearly the Co substitution at Fe site in SmFe1-xCoxAsO diminishes the Fe SDW character, introduces bulk superconductivity for x between 0.10 and 0.20 and finally becomes non-superconducting for x above 0.20. The Fe2+ site Co3+ substitution injects mobile electrons to the system and superconductivity appears, however direct substitution introduces simultaneous disorder in superconducting FeAs layer and thus superconductivity disappears for higher content of Co.Comment: 14 Pages Text + Figs comments ([email protected]

MicroRNA-223 Suppresses the Canonical NF-kB Pathway in Basal Keratinocytes to Dampen Neutrophilic Inflammation

MicroRNA-223 is known as a myeloid-enriched anti-inflammatory microRNA that is dysregulated in numerous inflammatory conditions. Here, we report that neutrophilic inflammation (wound response) is augmented in miR-223-deficient zebrafish, due pri- marily to elevated activation of the canonical nuclear factor kB (NF-kB) pathway. NF-kB over-activation is restricted to the basal layer of the surface epithelium, although miR-223 is detected throughout the epithe- lium and in phagocytes. Not only phagocytes but also epithelial cells are involved in miR-223-medi- ated regulation of neutrophils’ wound response and NF-kB activation. Cul1a/b, Traf6, and Tab1 are iden- tified as direct targets of miR-223, and their levels rise in injured epithelium lacking miR-223. In addi- tion, miR-223 is expressed in cultured human bron- chial epithelial cells, where it also downregulates NF-kB signaling. Together, this direct connection between miR-223 and the canonical NF-kB pathway provides a mechanistic understanding of the multi- faceted role of miR-223 and highlights the relevance of epithelial cells in dampening neutrophil activation

Synthesis and Physical Properties of FeSe1/2Te1/2 Superconductor

One of the most important properties of very recently reported FeSe based superconductors is the robustness of their superconductivity under applied magnetic field. The synthesis and control of superconductivity in FeSe based compounds is rather a difficult task. Synthesis and physical property characterization for optimized superconductivity of FeSe1/2Te1/2 at 13 K is reported here. The compound crystallized in a tetragonal structure with lattice parameters a = 3.8008(10) and c = 6.0187 (15) A. Magnetization measurements indicated bulk superconductivity with lower critical field (Hc1) of around 180 Oe. By applying Ginzburg Landau (GL) theory, the Hc2(0) value is estimated to be = 1840 kOe for the 90% of resistive transition. A heat capacity measurement revealed bulk superconductivity by a hump at Tc near 13 K, and an expected decrease was observed under an applied magnetic field.Comment: 13 pages text + Figs: commenta ([email protected]

Single-Step Synthesis of Sr4V2O6Fe2As2: The Blocking Layer Based Potential Future Superconductor

We report synthesis, structural details and transport measurements on Sr4V2O6Fe2As2. Namely, the stoichiometric amounts of V2O5+1/2xSrO(2)+7/2xSr+2xFeAs are weighed mixed, ground thoroughly and palletized in rectangular form in a glove box in high purity Ar atmosphere. The pellet is further sealed in an evacuated (10(-5) torr) quartz tube and put for heat treatments at 750 and 1150A degrees C in a single step for 12 and 36 hours respectively. Finally the quartz ampoule is allowed to cool naturally to room temperature. The as-synthesized sample is black in color. The compound crystallized in P4/nmm space group with lattice parameters a=b=3.925 and c=15.870 . Also seen are some small impurity lines. The compound did not exhibit superconductivity but instead a spin density wave (SDW) like metallic step at around 175 K is seen in R(T) measurements. Principally in [FeAs](-1){Sr4V2O6}(C)[FeAs](-1) the net value of blocking layer charge C must be either less or more than 2, to let it be electron or hole type superconductor respectively. Efforts are under way to achieve superconductivity in the studied system

Suppression of spin density wave character of (Sm/Gd)FeAsO by substitution of Ru at Fe site

We report synthesis, structural details and transport measurements on SmFe0.5Ru0.5AsO and GdFe0.5Ru0.5AsO. The samples are synthesized at normal pressure with vacuum encapsulation technique. The parent REFeAsO (RE = Sm and Gd) crystallizes in tetragonal P4/nmm space group having their lattice parameters as a = 3.9375(6) Å, c = 8.5021(4) Å for Sm and a = 3.9152(4) Å, c = 8.4546(1) Å for Gd. With 50% Ru substitution at Fe site i.e. for SmFe0.5Ru0.5AsO and GdFe0.5Ru0.5AsO the lattice parameter a is increased and c is decreased to as a = 4.0113(55) Å, c = 8.3129(17) Å for Sm and a = 3.9795(64) Å, c = 8.2787 (20) Å for Gd samples. Resistivity measurements on pristine samples though exhibited clearly the step like metallic transition at around 150 K, the Fe site 50% Ru substituted samples show all through a metallic behavior without the characteristic spin density wave (SDW) step. The samples with lower content of Ru at Fe site i.e. 10% and 30% are also studied. Though 10% Ru doped samples exhibited weak superconductivity like transition below 15 K, the 30% doped samples are metallic. It seems that the Fe2+ site Ru4+/5+ substitution provides electron carriers for conduction process. For achieving bulk superconductivity in Fe-site Ru substituted REFeAsO (1111) systems the efforts are still underway

Superconductivity and thermal properties of sulphur doped FeTe with effect of oxygen post annealing

Here, we report the synthesis and characterization of sulphur-substituted iron telluride i.e. FeTe1ÀxSx; (x = 0–30 %) system and study the impact of low temperature oxygen (O2) annealing as well. Rietveld analysis of room temperature X-ray diffraction (XRD) patterns shows that all the compounds are crystallized in a tetragonal structure (space group P4/nmm) and no secondary phases are observed. Lattice constants are decreased with increasing S concentration. The parent compound of the system i.e. FeTe does not exhibit superconductivity but shows an anomaly in the resistivity measurement at around 78 K, which corresponds to a structural phase transition. Heat capacity Cp(T) measurement also confirms the structural phase transition of FeTe compound. Superconductivity appears by S substitution; the onset of superconducting transition temperature is about 8 K for FeTe0.75S0.25 sample. Thermoelectric power measurements S(T) also shows the superconducting transition at around 7 K for FeTe0.75S0.25 sample. The upper critical fields Hc2(10%), Hc2(50%) and Hc2(90%) are estimated to be 400, 650 and 900 kOe respectively at 0 K by applying Ginzburg Landau (GL) equation. Interestingly, superconducting volume fraction is increased with low temperature (200 °C) O2 annealing at normal pressure. Detailed investiga- tions related to structural (XRD), transport [S(T), R(T)H], magnetization (AC and DC susceptibility) and thermal [Cp(T)] measurements for FeTe1ÀxS:O2 system are presented and discusse