2,108 research outputs found

    Ammonia formation caused by the presence of water in the wet grinding of silicon nitride powder

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    Si3 N4 powder (amorphous, alpha-, and beta-Si3 N4) was mixed with MeOH containing 8.87 mol. % H2O and ground. The NH3 generation rapidly increased after a grinding time of 100 hours. Silicon nitride sintered material was chosen as one of the high temperature, high strength structural materials and studies of the control of the raw material powder, preparation of the sintered body (finding the right assistant, hot press, high pressure sintering, fracture toughness and oxidation at high temperature were performed

    Reduction of critical field for magnetic and orbital-ordering phase transition in impurity-substituted Nd0.45_{0.45}Sr0.55_{0.55}MnO3_3 crystal

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    We have investigated the Mn-site substitution effect in Nd0.45_{0.45}Sr0.55_{0.55}MnO3_3 single crystal, which has an AA-type layered antiferromagnetic (AA-AFM) phase with the 3dx2−y2d_{x^2-y^2}-type orbital-order. Substitution of Fe or Ga for Mn-site suppresses both the AA-AFM order and competing ferromagnetic (FM) correlation whereas Cr substitution suppresses only the AA-AFM order but reactivates the underlying FM correlation via double-exchange mechanism along the AFM coupled cc-direction. In Nd0.45_{0.45}Sr0.55_{0.55}Mn0.95_{0.95}Cr0.05_{0.05}O3_3, the AA-AFM state with the orbital-order is changed into the orbital-disordered three-dimensional FM metallic state by applying magnetic field of μ0H=12\mu_0 H = 12 T, which is much smaller than that of the parent compound Nd0.45_{0.45}Sr0.55_{0.55}MnO3_3.Comment: 5 pages, 4 figures, to appear in APL Material

    Refinement Type Inference via Horn Constraint Optimization

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    We propose a novel method for inferring refinement types of higher-order functional programs. The main advantage of the proposed method is that it can infer maximally preferred (i.e., Pareto optimal) refinement types with respect to a user-specified preference order. The flexible optimization of refinement types enabled by the proposed method paves the way for interesting applications, such as inferring most-general characterization of inputs for which a given program satisfies (or violates) a given safety (or termination) property. Our method reduces such a type optimization problem to a Horn constraint optimization problem by using a new refinement type system that can flexibly reason about non-determinism in programs. Our method then solves the constraint optimization problem by repeatedly improving a current solution until convergence via template-based invariant generation. We have implemented a prototype inference system based on our method, and obtained promising results in preliminary experiments.Comment: 19 page

    Enhancement of the anomalous Hall effect and spin glass behavior in the bilayered manganite La(2-2x)Sr(1+2x)Mn2O7

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    The Hall resistivity and magnetization have been investigated in the ferromagnetic state of the bilayered manganite La(2-2x)Sr(1+2x)Mn2O7 (x=0.36). The Hall resistivity shows an increase in both the ordinary and anomalous Hall coefficients at low temperatures below 50K, a region in which experimental evidence for the spin glass state has been found in a low magnetic field of 1mT. The origin of the anomalous behavior of the Hall resistivity relevant to magnetic states may lie in the intrinsic microscopic inhomogeneity in a quasi-two-dimensional electron system.Comment: 7 pages, 4 figures, Solid State Communications (in press

    Competition between ferromagnetic and charge-orbital ordered phases in Pr1−x_{1-x}Cax_{x}MnO3_3 for xx=1/4, 3/8, and 1/2

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    Spin, charge, and orbital structures in models for doped manganites are studied by a combination of analytic mean-field and numerical relaxation techniques. At realistic values for the electron-phonon and antiferromagnetic t2gt_{2g} spin couplings, a competition between a ferromagnetic (FM) phase and a charge-orbital ordered (COO) insulating state is found for xx=1/4, 3/8, and 1/2, as experimentally observed in Pr1−x_{1-x}Cax_{x}MnO3_3 for xx=0.3∼\sim0.5. The theoretical predictions for the spin-charge-orbital ordering pattern are compared with experiments. The FM-COO energy difference is surprisingly small for the densities studied, result compatible with the presence of a robust colossal-magnetoresistive effect in Pr1−x_{1-x}Cax_{x}MnO3_3 in a large density interval.Comment: 4 pages, Revtex, with 2 figures embedded in the text. Submitted to Phys. Rev.

    Chemical potential shift induced by double-exchange and polaronic effects in Nd_{1-x}Sr_xMnO_3

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    We have studied the chemical potential shift as a function of temperature in Nd1−x_{1-x}Srx_xMnO3_3 (NSMO) by measurements of core-level photoemission spectra. For ferromagnetic samples (x=0.4x=0.4 and 0.45), we observed an unusually large upward chemical potential shift with decreasing temperature in the low-temperature region of the ferromagnetic metallic (FM) phase. This can be explained by the double-exchange (DE) mechanism if the ege_g band is split by dynamical/local Jahn-Teller effect. The shift was suppressed near the Curie temperature (TCT_C), which we attribute to the crossover from the DE to lattice-polaron regimes.Comment: 5 pages, 6 figure
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