99 research outputs found
Three Dimensional Superconductivity in FeSe with Tczero Up to 10.9 K Induced by Internal Strain
Polycrystalline sample FeSe was synthesized by a self-flux solution method
which shows a zero resistance temperature up to 10.9 K and a Tconset (90%
\rhon, \rhon: normal state resistivity) up to 13.3 K. The decrease of
superconducting transition temperature by heat treatment indicates that
internal crystallographic strain which plays the same effect as external
pressure is the origin of its high Tc. The fluctuation conductivity was studied
which could be well described by 3D Aslamazov-Larkin (AL) power law. The
estimated value of coherence length \xic=9.2 \AA is larger than the distance
between conducting layers (~6.0 \AA), indicating the three-dimensional nature
of superconductivity in this compound.Comment: 5 figure
Vacuum Filling Simulation with Combined Lagranian and VOF Method
Jetting succeeded by accumulation is the characteristic of the vacuum filling, which is different from the conventional pressure-driven flow. In order to simulate this kind of flow, a three-dimensional theoretical model in terms of incompressible and viscous flow is established, and an iterative method combined with finite element method (FEM) is proposed to solve the flow problem. The Lagranian-VOF method is constructed to trace the jetting and accumulated flow fronts. Based on the proposed model and algorithm, a simulation program is developed to predict the velocity, pressure, temperature, and advancement progress. To validate the model and algorithm, a visual experimental equipment for vacuum filling is designed and construted. The vacuum filling experiments with different viscous materials and negative pressures were conducted and compared the corresponding simulations. The results show the flow front shape closely depends on the fluid viscosity and less relates to the vacuum pressure
Magnetic field induced discontinuous spin reorientation in ErFeO3 single crystal
The spin reorientation of ErFeO3 that spontaneously occurs at low temperature has been previously determined to be a process involving the continuous rotation of Fe3þ spins. In this work, the dynamic process of spin reorientation in ErFeO3 single crystal has been investigated by AC susceptibility measurements at various frequencies and static magnetic fields. Interestingly, two completely discontinuous steps are induced by a relatively large static magnetic field due to the variation in the magnetic anisotropy during this process. It provides deeper insights into the intriguing magnetic exchange interactions which dominate the sophisticated magnetic phase transitions in the orthoferrite systems
Structure and Electronic Properties of SrTiO3–TiO2 Eutectic for Water Splitting Applications
Semiconductors with bandgaps and edges corresponding to the solar energy spectrum are found to be suitable for the water splitting applications using photoelectrochemical reactions. However, many present-day materials used in these applications do not have high stability and/or high effectiveness over the complete sunlight spectral range. The recently proposed eutectic compounds, which combine two or more semiconducting materials, can overcome many present difficulties and extend the light absorbance spectrum improving the effectiveness of the water splitting cells. Herein, structural and electronic properties studies of the SrTiO3–TiO2 eutectic material, which is a representative example of this family, are presented. It is found that structural properties of this material, particularly the phase separation and formation of the sharp interface between two phases, can be significantly improved up on the thermal annealing, which is very important for their application in the water splitting reactors. The findings present the deep understanding of the interface structure and electronic properties of the SrTiO3–TiO2 eutectic, which can help to improve the functionality of these class of materials in different applications
A New Viscoelastic Model for Polycarbonate Compressing Flow
To overcome the weakness of conventional models in describing compressing flow especially in start and end stages the shear rate derivative was added to the right side of PTT constitutive equation. The ability of describing the well-known ‘shear shinning’ and ‘stretch harden’ phenomena was first illustrated by theoretical analysis. Then the governing equations for compressing flow were established in terms of incompressible and isothermal fluid, and the numerical method was constructed to discretize the equations and get the compressing flow solutions. The experiments with four melt temperatures were conducted and the corresponding simulations were performed. The better agreements with experimental data indicates the modified PPT model is superior to the original PTT model in prediction of compressing flow. In addition, the proposed model is also validated with low and high compressing speed experiments
Spin and charge density waves in the quasi-one-dimensional KMn6Bi5
AMn6Bi5 materials (A = Na, K, Rb and Cs) consisting of unique Mn-cluster
chains emerge as a new family of superconductors with the suppression of their
antiferromagnetic (AFM) order under high pressures. Here, we report transverse
incommensurate spin density waves (SDWs) for the Mn atoms with a propagating
direction along the chain axes as a ground state for KMn6Bi5 by single crystal
neutron diffraction. The SDWs have a refined amplitude of ~2.46 Bohr magnetons
for the Mn atoms in the pentagons and ~0.29 Bohr magnetons with a large
standard deviation for Mn atoms in the center between the pentagons. AFM
dominate both the nearest-neighbor Mn-Mn interactions within the pentagon and
next-nearest-neighbor Mn-Mn interactions out of the pentagon (along the
propagating wave). The SDWs exhibit both local and itinerant characteristics
probably formed by a cooperative interaction between local magnetic exchange
and conduction electrons. A significant magnetoelastic effect during the AFM
transition, especially along the chain direction, has been demonstrated by
temperature-dependent x-ray powder diffraction. Single crystal x-ray
diffraction below the AFM transition revealed satellite peaks originating from
charge density waves along the chain direction with a q-vector twice as large
as the SDW one, pointing to a strong real space coupling between them. Our work
not only manifests a fascinating interplay among spin, charge, lattice and one
dimensionality to trigger intertwined orders in KMn6Bi5 but also provides
important piece of information for the magnetic structure of the parent
compound to understand the mechanism of superconductivity in this new family
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