361 research outputs found
Superconductivity suppression of Ba0.5K0.5Fe2-2xM2xAs2 single crystals by substitution of transition-metal (M = Mn, Ru, Co, Ni, Cu, and Zn)
We investigated the doping effects of magnetic and nonmagnetic impurities on
the single-crystalline p-type Ba0.5K0.5Fe2-2xM2xAs2 (M = Mn, Ru, Co, Ni, Cu and
Zn) superconductors. The superconductivity indicates robustly against impurity
of Ru, while weakly against the impurities of Mn, Co, Ni, Cu, and Zn. However,
the present Tc suppression rate of both magnetic and nonmagnetic impurities
remains much lower than what was expected for the s\pm-wave model. The
temperature dependence of resistivity data is observed an obvious low-T upturn
for the crystals doped with high-level impurity, which is due to the occurrence
of localization. Thus, the relatively weak Tc suppression effect from Mn, Co,
Ni, Cu, and Zn are considered as a result of localization rather than
pair-breaking effect in s\pm-wave model.Comment: 8 pages, 9 figures, to be published in Phys. Rev.
Continuous metal-insulator transition of the antiferromagnetic perovskite NaOsO3
Newly synthesized perovskite NaOsO3 shows Curie-Weiss metallic nature at high
temperature and suddenly goes into an antiferromagnetically insulating state at
410 K on cooling. Electronic specific heat at the low temperature limit is
absent, indicating that the band gap fully opens. In situ observation in
electron microscopy undetected any lattice anomalies in the vicinity of the
transition temperature. It is most likely that the antiferromagnetic
correlation plays an essential role of the gap opening.Comment: 13 pages, 5 figures, PHYS. REV. B 80, 161104(R),(2009
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]
Structural Order Parameter in the Pyrochlore Superconductor Cd2Re2O7
It is shown that both structural phase transitions in Cd2Re2O7, which occur
at T_{s1}=200 K and T_{s2}=120 K, are due to an instability of the Re
tetrahedral network with respect to the same doubly degenerate long-wavelength
phonon mode. The primary structural order parameter transforms according to the
irreducible representation E_u of the point group O_h. We argue that the
transition at T_{s1} may be of second order, in accordance with experimental
data. We obtain the phase diagram in the space of phenomenological parameters
and propose a thermodynamic path that Cd2Re2O7 follows upon cooling. Couplings
of the itinerant electronic system and localized spin states in pyrochlores and
spinels to atomic displacements are discussed.Comment: 5 pages. Submitted to J. Phys. Soc. Jpn. Best quality figures are
available at http://www.physics.mun.ca/~isergien/pubs.htm
Changes in the expression of miRNAs at the pericentral and periportal regions of the rat liver in response to hepatocellular injury: comparison with the changes in the expression of plasma miRNAs
MicroRNAs (miRNAs) in body fluids have received attention as potential biomarkers of organ damage because miRNAs that are highly or specifically expressed in a given organ are likely released into body fluids as a result of damage to that organ. We previously determined that the plasma miRNA profile in rats was dramatically changed due to acetaminophen (APAP)-induced pericentral necrosis and methapyrilene (MP)-induced periportal necrosis in the liver. The purpose of this study was to examine whether the expression of hepatic miRNAs is differentially modulated at different zones due to injury and to examine the relationship of the hepatic miRNA profile with the changes in the plasma miRNA expression profile. Through the laser microdissection of the periportal and periportal regions of the liver and TaqMan microRNA Array analysis, we found that 49 miRNAs are differentially expressed between the pericentral and periportal regions of control rats. In both APAP- and MP-treated rats, the miRNAs that presented decreased expression dominated in both the injured and non-injured areas compared with the miRNAs that exhibited increased expression. The changes in miRNA expression in each region of the liver were compared with those observed in the plasma. Of the 301 plasma miRNAs with expression that was changed as a result of APAP administration, only 21% were changed in the injured area of the liver. Of the 263 plasma miRNAs with expression that was changed due to MP administration, only 24% were changed in the injured area of the liver. Thus, the miRNA expression profiles in the plasma do not merely reflect the release of miRNAs from the damaged cells in the liver. This report provides the first demonstration of zonal miRNA expression in the liver and of the relationship of the miRNA expression profile in a tissue with the plasma miRNA profile. © 2014 Elsevier Ireland Ltd
Magnetic and electrical properties and carrier doping effects on the Fe-based host compound Sr4Sc2Fe2As2O6
Additional charge carriers were introduced to the iron oxyarsenide
Sr4Sc2Fe2As2O6 under a high-pressure condition, followed by measurements of
electrical resistivity, Hall coefficient, and magnetic susceptibility. The host
compound Sr4Sc2Fe2As2O6 shows metallic conductivity down to ~200 K and turns to
show a semiconducting-like conductivity accompanied by a positive
magneto-resistance (22% at 70 kOe). Although the carrier density is comparable
at 300 K (5.9x1021 cm-3) with that of the other Fe-based superconductors, no
superconductivity appears down to 2 K. This is primarily because the net
carrier density decreases over 3 orders of magnitude on cooling and
additionally a possible magnetic order at ~120 K prevents carriers from
pairing. The properties were altered largely by introducing the additional
carriers.Comment: 22 pages, 9 figures, 1 table, 41 references, accepted Phys. Rev. B
201
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]
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