123 research outputs found

    Relevance of Cooperative Lattice Effects and Correlated Disorder in Phase-Separation Theories for CMR Manganites

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    Previous theoretical investigations of colossal magnetoresistance (CMR) materials explain this effect using a ``clustered'' state with preformed ferromagnetic islands that rapidly align their moments with increasing external magnetic fields. While qualitatively successful, explicit calculations indicate drastically different typical resistivity values in two- and three-dimensional lattices, contrary to experimental observations. This conceptual bottleneck in the phase-separated CMR scenario is resolved here considering the cooperative nature of the Mn-oxide lattice distortions. This induces power-law correlations in the quenched random fields used in toy models with phase competition. When these effects are incorporated, resistor-network calculations reveal very similar results in two and three dimensions, solving the puzzle.Comment: RevTeX 4, 4 figure

    Rotary machine having back to back turbines

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    A rotary machine having a pair of back to back turbines in serial flow relationship is disclosed. Various construction details are developed which permit for a compact design. In one detailed embodiment the turbine has a housing having an inlet manifold and an exit manifold which are disposed between the outlet manifold for an associated turbopump

    An integrated study of earth resources in the State of California using remote sensing techniques

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    The author has identified the following significant results. The supply, demand, and impact relationships of California's water resources as exemplified by the Feather River project and other aspects of the California Water Plan are discussed

    An integrated study of earth resources in the state of California using remote sensing techniques

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    The University of California has been conducting an investigation which seeks to determine the usefulness of modern remote sensing techniques for studying various components of California's earth resources complex. Most of the work has concentrated on California's water resources, but with some attention being given to other earth resources as well and to the interplay between them and California's water resources

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

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    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

    A Duality Between Unidirectional Charge Density Wave Order and Superconductivity

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    This paper shows the existence of a duality between an unidirectional charge density wave order and a superconducting order. This duality predicts the existence of charge density wave near a superconducting vortex, and the existence of superconductivity near a charge density wave dislocation.Comment: Main results are the same, but the presentation is significantly modified. To appear in Physical Review Letter

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

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    Versatile features of impurity doping effects on perovskite manganites, R0.6R_{0.6}Sr0.4_{0.4}MnO3_{3}, have been investigated with varying the doing species as well as the RR-dependent one-electron bandwidth. In ferromagnetic-metallic manganites (RR=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 RR species, the phase diagram as a function of Fe concentration is closely similar to that for R0.6R_{0.6}Sr0.4_{0.4}MnO3_{3} obtained by decreasing the ionic radius of RR 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 (RR=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

    Inhomogeneous magnetism in single crystalline Sr3_3CuIrO6+δ_{6+\delta}: Implications to phase-separation concepts

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    The single crystalline form of an insulator, Sr3_3CuIrO6+δ_{6+\delta}, is shown to exhibit unexpectedly more than one magnetic transition (at 5 and 19 K) with spin-glass-like magnetic susceptibility behaviour. On the basis of this finding, viz., inhomogeneous magnetism in a chemically homogeneous material, we propose that the idea of "phase- separation" described for manganites [1] is more widespread in different ways. The observed experimental features enable us to make a comparison with the predictions of a recent toy model [2] on {\it magnetic} phase separation in an insulating environment.Comment: 4 pages, 4 figure
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