3,161 research outputs found
Computational screening of magnetocaloric alloys
An exciting development over the past few decades has been the use of
high-throughput computational screening as a means of identifying promising
candidate materials for a variety of structural or functional properties.
Experimentally, it is often found that the highest-performing materials contain
substantial atomic site disorder. These are frequently overlooked in
high-throughput computational searches however, due to difficulties in dealing
with materials that do not possess simple, well-defined crystallographic unit
cells. Here we demonstrate that the screening of magnetocaloric materials with
the help of the density functional theory-based magnetic deformation proxy can
be extended to systems with atomic site disorder. This is accomplished by
thermodynamic averaging of the magnetic deformation for ordered supercells
across a solid solution. We show that the highly non-monotonic magnetocaloric
properties of the disordered solid solutions Mn(CoFe)Ge and
(MnNi)CoGe are successfully captured using this method.Comment: Main text: 8 pages, 6 figures. Supplemental Material: 2 pages, 2
figure
PROTON STRUCTURE FUNCTION CALCULATION BY THERMODYNAMICAL BAG MODEL
This paper focuses on finding proton structure functions in deep inelastic scattering of leptons on nucleons by MIT Bag model. This model proposed by V. Devanathan and S. Karthiyayini assumes that nucleon is a hot bag containing quarks, which interact with bosons. The nucleon structure function is then expressed in terms of Parton distribution functions where both are functions of Bjorken variable ð‘¥ only. The structure functions calculated by this model are found to be in good agreement with the data obtained from CERN for Bjorken variable ð‘¥ greater than 0.2 only
Real space investigation of structural changes at the metal-insulator transition in VO2
Synchrotron X-ray total scattering studies of structural changes in rutile
VO2 at the metal-insulator transition temperature of 340 K reveal that
monoclinic and tetragonal phases of VO2 coexist in equilibrium, as expected for
a first-order phase transition. No evidence for any distinct intermediate phase
is seen. Unbiased local structure studies of the changes in V--V distances
through the phase transition, using reverse Monte Carlo methods, support the
idea of phase coexistence and point to the high degree of correlation in the
dimerized low-temperature structure. No evidence for short range V--V
correlations that would be suggestive of local dimers is found in the metallic
phase.Comment: 4 pages, 5 figure
Spin-induced symmetry breaking in orbitally ordered NiCr_2O_4 and CuCr_2O_4
At room temperature, the normal oxide spinels NiCr_2O_4 and CuCr_2O_4 are
tetragonally distorted and crystallize in the I4_1/amd space group due to
cooperative Jahn-Teller ordering driven by the orbital degeneracy of
tetrahedral Ni () and Cu (). Upon cooling, these
compounds undergo magnetic ordering transitions; interactions being somewhat
frustrated for NiCr_2O_4 but not for CuCr_2O_4. We employ variable-temperature
high-resolution synchrotron X-ray powder diffraction to establish that at the
magnetic ordering temperatures there are further structural changes, which
result in both compounds distorting to an orthorhombic structure consistent
with the Fddd space group. NiCr_2O_4 exhibits additional distortion, likely
within the same space group, at a yet-lower transition temperature of = 30
K. The tetragonal to orthorhombic structural transition in these compounds
appears to primarily involve changes in NiO_4 and CuO_4 tetrahedra
Moduli of parahoric G-torsors on a compact Riemann surface
Let χ be an irreducible smooth projective algebraic curve of genus g ≥ 2 over the ground field C and let G be a semisimple simply connected algebraic group. The aim of this paper is to introduce the notion of a semistable and stable parahoric torsor under a certain Bruhat-Tits group scheme G, construct the moduli space of semistable parahoric G-torsors and identify the underlying topological space of this moduli space with certain spaces of homomorphisms of Fuchsian groups into a maximal compact subgroup of G. The results give a complete generalization of the earlier results of Mehta and Seshadri on parabolic vector bundles
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