Incommensurate spin correlations in highly oxidized cobaltates La2−x_{2-x}Srx_{x}CoO4_{4}

We observe quasi-static incommensurate magnetic peaks in neutron scattering experiments on layered cobalt oxides La2-xSrxCoO4 with high Co oxidation states that have been reported to be paramagnetic. This enables us to measure the magnetic excitations in this highly hole-doped incommensurate regime and compare our results with those found in the low-doped incommensurate regime that exhibit hourglass magnetic spectra. The hourglass shape of magnetic excitations completely disappears given a high Sr doping. Moreover, broad low-energy excitations are found, which are not centered at the incommensurate magnetic peak positions but around the quarter-integer values that are typically exhibited by excitations in the checkerboard charge ordered phase. Our findings suggest that the strong inter-site exchange interactions in the undoped islands are critical for the emergence of hourglass spectra in the incommensurate magnetic phases of La2-xSrxCoO4.Comment: http://www.nature.com/articles/srep25117

Magnetic and charge transport properties of the Na-based Os oxide pyrochlore

Na-based osmium oxide pyrochlore was synthesized for the first time by an ion-exchange method. KOs2O6 was used as a host compound. Elelectron probe micro-analysis, synchrotron x-ray diffraction analysis, and thermo-gravimetric analysis confirmed its structure not as the beta-type but as the defect-type pyrochlore. The composition was identified as Na1.4Os2O6.H2O. Electrical resistivity, heat capacity, and magnetization measurements of the polycrystalline Na1.4Os2O6.H2O clarified absence of superconductivity above 2 K, being in contrast to what were found for the beta-pyrochlore AOs2O6 (A = Cs, Rb, K). Sommerfeld coefficient of 22 mJ K-2 mol-1 of Na1.4Os2O6.H2O was smallest among those of AOs2O6. A magnetic anomaly at ~57 K and possible associated magnetoresistance (+3.7 % at 2 K in 70 kOe) were found.Comment: 19 pages, 6 figures, Submitted to PR

Trisodium dihydroxotetraoxoosmate(VII), Na3[OsO4(OH)2]

Na-3[OsO4(OH)(2)] contains osmium(VII) coordinated octahedrally by four oxide and two hydroxide groups. The OsO4(OH)(2) octahedra form zigzag chains parallel to [010], linked by hydrogen bridges. Two O atoms, one Na and the Os atom lie on a mirror plane

Syntheses and crystal structures of two sodium ruthenates: Na2RuO4 and Na2RuO3

Na2RuO4, prepared from Na2O2 and RuO2 via high oxygen pressure synthesis, crystallises monoclinic in space group P2(1)/c (a = 10.721(6), b = 7.033(4), c = 10.871(6) Angstrom, beta = 119.10(4)degrees, Z = 8, 2503 unique reflections, R-1 = 0.049). Structure determination from single crystal data shows that the compound consists of infinite chains of RuO5 trigonal bipyramids connected through their axial vertices. The Na cations connect the pseudohexagonally packed (1)(infinity)[RuO3O2/2] chains and are coordinated by six or seven oxygen atoms, respectively. The compound exhibits an one-dimensional spin system with mu = 2.80 mu(B) and Theta = -222 K and a three-dimensional antiferromagnetic ordering below 50 K. Na2RuO3 was obtained from Na2RuO4 at 850 degreesC under a flow of argon. The structure was determined from X-ray powder diffraction. It is closely related to the alpha-NaFeO2 and the Li2SnO3 structure types, layered variants of the NaCl type. In Na2RuO3 the Na and Ru atoms are partially disordered. This partially disordered state was approximated by a Rietveld refinement of two superimposed structural models (model I: R (3) over bar m, a = 3.12360(5), c = 16.0370(4) Angstrom, Z = 2; model II: C2/c, a = 5.4141(4), b = 9.3663(6), c = 10.8481(4) Angstrom, beta = 99.636(9)degrees, Z = 8)

Neutron diffraction study of the magnetic structure of Na 2 RuO 4

Nuclear and magnetic structures of sodium ruthenate (VI) have been studied by neutron powder diffraction in the temperature range 1.5–200 K. Na 2RuO 4 crystallizes in the monoclinic structure, with space group P 2 1/c. The structure consists of apical corner sharing RuO 5 trigonal bipyramids forming infinite chains running along the b axis. These infinite [ RuO 3O 2/2 ] chains form a pseudo hexagonal close packing of rods with Ru–Ru distances of 3.51 Å within the chains and 5.30–5.47 Å between the chains. At T N=37.2 K a magnetic transition leads to an antiferromagnetic state. The Ru 6+ magnetic moments are ordered antiferromagnetically along the chains (b-axis), while the inter-chain interaction is ferromagnetic. A classical infinite chain model was fitted to the magnetic susceptibility data in order to estimate the strength of the nearest-neighbor exchange interactions along and between the chains, resulting in an intrachain coupling parameter of 2J=-86 K, and an interchain parameter J ⊥ with $\vert$ 2J ⊥ $\vert$  = 3 K. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200674.70.Pq Ruthenates, 75.25.+z Spin arrangements in magnetically ordered materials, 75.50.Ee Antiferromagnetics,

A neutron scattering study of the crystal and magnetic structure of Sr2CrOsO6

Recently, the new osmium based ferrimagnetic double perovskite Sr2CrOsO6 has been reported to have the highest Curie temperature 725 K within this material class [Y. Krockenberger, K. Mogare, M. Reehuis, M. Tovar, M. Jansen, G. Vaitheeswaran, V. Kanchana, A. Delin, F. Wilhelm, A. Rogalev, A. Winkler, L. Alff, preprint, 2006]. Here, we report details about the crystal and magnetic structure of Sr2CrOsO6 as obtained by neutron powder diffractio

Lead-induced upregulation of the heme-regulated eukaryotic initiation factor 2α kinase is compromised by hemin in human K562 cells

Expression and kinase activity of the heme-regulated-eIF-2α kinase or -inhibitor (HRI) are induced during cytoplasmic stresses leading to inhibition of protein synthesis. Using a reporter construct with HRI promoter, we have determined the promoter activity during heat-shock and lead toxicity in human K562 cells. These two conditions induced HRI promoter activity by 2- to 3-fold. Contrary to this, hemin, a suppressor of HRI kinase activity, downregulated HRI promoter activity and stimulated hemoglobin synthesis. Interestingly, when hemin-treated cells were transfected and exposed to lead, hemin compromised lead-effect substantially by downregulating HRI promoter activity, HRI transcription and HRI kinase activity. These results together suggest that heme signaling in relation to translation regulation is not only restricted to the cytoplasm (modulating HRI kinase activity) alone but it also spans to the nucleus modulating HRI expression. Hemin may thus be useful for alleviation of stress-induced inhibition of protein synthesis

Weak orbital ordering of Ir t 2g states in the double perovskite Sr2CeIrO6

The electronic and magnetic properties of distorted monoclinic double perovskite Sr2CeIrO6 were examined based on both experiments and first principles density functional theory calculations. From the calculations we conclude that low spin state Ir4 5d5 forms a rare weakly antiferromagnetic AFM orbital ordered state derived from alternating occupation of slightly mixed c g pi symmetry states in the presence of spin orbit coupling SOC . This orbital ordering is caused due to the competition between the comparable strength of Jahn Teller structural distortion and SOC. We found both electron electron correlation and SOC are required to drive the experimentally observed AFM insulating ground state. Electronic structure investigation suggests that this material belongs to the intermediate SOC regime, by comparing our results with the other existing iridates. This single active site double perovskite provides a rare platform with a prototype geometrically frustrated fcc lattice where among the different degrees of freedom i.e., spin, orbital, and lattice SOC, structural distortion, and Coulomb correlation energy scales compete and interact with each othe