1,351 research outputs found
Ab Initio Exchange Interactions and Magnetic Properties of Intermetallic Compound Gd(2)Fe(17-x)Ga(x)
Intermetallic compounds R2Fe17 are perspective for applications as permanent
magnets. Technologically these systems must have Curie temperature Tc much
higher than room temperature and preferably have easy axis anisotropy. At the
moment highest Tc among stoichiometric R2Fe17 materials is 476 K, which is not
high enough. There are two possibilities to increase Tc: substitution of Fe
ions with non-magnetic elements or introduction of light elements into
interstitial positions. In this work we have focused our attention on
substitution scenario of Curie temperature rising observed experimentally in
Gd(2)Fe(17-x)Ga(x) (x=0,3,6) compounds. In the framework of the LSDA approach
electronic structure and magnetic properties of the compounds were calculated.
Ab initio exchange interaction parameters within the Fe sublattice for all
nearest Fe ions were obtained. Employing the theoretical values of exchange
parameters Curie temperatures Tc of Gd(2)Fe(17-x)Ga(x) within mean-field theory
were estimated. Obtained values of Tc agree well with experiment. Also LSDA
computed values of total magnetic moment coincide with experimental ones.Comment: 4 pages, 4 figures, 4 tables, Proceedings for EASTMAG-2010, June 28 -
July 2 2010, Ekaterinburg, Russi
Novel multiple-band superconductor SrPt2As2
We present LDA calculated electronic structure of recently discovered
superconductor SrPt2As2 with Tc=5.2K. Despite its chemical composition and
crystal structure are somehow similar to FeAs-based high-temperature
superconductors, the electronic structure of SrPt2As2 is very much different.
Crystal structure is orthorhombic (or tetragonal if idealized) and has layered
nature with alternating PtAs4 and AsPt4 tetrahedra slabs sandwiched with Sr
ions. The Fermi level is crossed by Pt-5d states with rather strong admixture
of As-4p states. Fermi surface of SrPt2As2 is essentially three dimensional,
with complicated sheets corresponding to multiple bands. We compare SrPt2As2
with 1111 and 122 representatives of FeAs-class of superconductors, as well as
with isovalent (Ba,Sr)Ni2As2 superconductors. Brief discussion of
superconductivity in SrPt2As2 is also presented.Comment: 5 pages, 4 figure
Electronic Structure of New Multiple Band Pt-Pnictide Superconductors APt3P
We report LDA calculated band structure, densities of states and Fermi
surfaces for recently discovered Pt-pnictide superconductors APt3P
(A=Ca,Sr,La), confirming their multiple band nature. Electronic structure is
essentially three dimensional, in contrast to Fe pnictides and chalcogenides.
LDA calculated Sommerfeld coefficient agrees rather well with experimental
data, leaving little space for very strong coupling superconductivity,
suggested by experimental data on specific heat of SrPt3P. Elementary estimates
show, that the values of critical temperature can be explained by rather weak
or moderately strong coupling, while the decrease of superconducting transition
temperature Tc from Sr to La compound can be explained by corresponding
decrease of total density of states at the Fermi level N(E_F). The shape of the
density of states near the Fermi level suggests that in SrPt3P electron doping
(such as replacement Sr by La) decreases N(E_F) and Tc, while hole doping (e.g.
partial replacement of Sr with K, Rb or Cs, if possible) would increase N(E_F)
and possibly Tc.Comment: 5 pages, 5 figure
Neutron-irradiation effects in LaO0.9F0.1FeAs superconductor
The effect of atomic disorder induced by neutrons irradiation on
superconducting and normal state properties of polycrystalline LaFeAsO_0.9F_0.1
was investigated. The irradiation of the sample by a moderate neutron fluence F
= 1.6*1019 cm^-2 at Tirr = 50 +- 10 C leads to the suppression of
superconductivity which recovers almost completely after annealing at
temperatures Tann < 750 C. It is shown that the reduction of superconducting
transition temperature Tc under atomic disordering is not determined solely by
the value of Hall concentration nH, i.e. doping level, but is governed by the
reduction of electronic relaxation time. This behavior can be described
qualitatively by universal Abrikosov-Gorkov equation which presents evidence on
the anomalous type of electrons pairing in Fe-based superconductors.Comment: 8 pages, 11 figure
Generalized dynamical mean-field theory in physics of strongly correlated systems
This review is devoted to generalization of dynamical mean-field theory
(DMFT) for strongly correlated electronic systems towards the account of
different types of additional interactions, necessary for correct physical
description of many experimentally observed phenomena in such systems. As
additional interactions we consider: (1) interaction of electrons with
antiferromagnetic (or charge) fluctuations of order parameter in high-Tc
superconductors leading to the formation of pseudogap state, (2) scattering of
electrons on static disorder and its role in general picture of
Anderson-Hubbard metal-insulator transition, (3) electron-phonon interaction
and corresponding anomalies of electronic spectra in strongly correlated
systems. Proposed DMFT+Sigma approach is based on taking into account above
mentioned interactions by introducing additional self-energy Sigma (in general
momentum dependent) into conventional DMFT scheme and calculated in a
self-consistent way within the standard set of DMFT equations. Here we
formulate general scheme of calculation of both one-particle (spectral
functions and densities of states) and two-particle (optical conductivity)
properties. We examine the problem of pseudogap formation, including the Fermi
arc formation and partial destruction of the Fermi surface, metal-insulator
transition in disordered Anderson-Hubbard model, and general picture of kink
formation within electronic spectra in strongly correlated systems. DMFT+Sigma
approach is generalized to describe realistic materials with strong
electron-electron correlations based on LDA+DMFT method. General scheme of
LDA+DMFT method is presented together with some of its applications to real
systems. The LDA+DMFT+Sigma approach is employed to modelling of pseudogap
state of electron and hole doped high-T_c cuprates. Comparison with variety of
ARPES experiments is given.Comment: 60 pages, 24 figures. Review article accepted for publication in
Physics-Uspekh
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