146 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
Theoretical investigation of TbNi_{5-x}Cu_x optical properties
In this paper we present theoretical investigation of optical conductivity
for intermetallic TbNi_{5-x}Cu_x series. In the frame of LSDA+U calculations
electronic structure for x=0,1,2 and on top of that optical conductivities were
calculated. Disorder effects of Ni for Cu substitution on a level of LSDA+U
densities of states (DOS) were taken into account via averaging over all
possible Cu ion positions for given doping level x. Gradual suppression and
loosing of structure of optical conductivity at 2 eV together with simultaneous
intensity growth at 4 eV correspond to increase of Cu and decrease of Ni
content. As reported before [Knyazev et al., Optics and Spectroscopy 104, 360
(2008)] plasma frequency has non monotonic doping behaviour with maximum at
x=1. This behaviour is explained as competition between lowering of total
density of states on the Fermi level N(E_F) and growing of number of carriers.
Our theoretical results agree well with variety of recent experiments.Comment: 4 pages, 3 figure
Ab initio exchange interactions and magnetic properties of Gd2Fe17 iron sublattice: rhombohedral vs. hexagonal phases
In the framework of the LSDA+U method electronic structure and magnetic
properties of the intermetallic compound Gd2Fe17 for both rhombohedral and
hexagonal phases have been calculated. On top of that, ab initio exchange
interaction parameters within the Fe sublattice for all present nearest and
some next nearest Fe ions have been obtained. It was found that for the first
coordination sphere direct exchange interaction is ferromagnetic. For the
second coordination sphere indirect exchange interaction is observed to be
weaker and of antiferromagnetic type. Employing the theoretical values of
exchange parameters Curie temperatures Tc of both hexagonal and rhombohedral
phases of Gd2Fe17 within Weiss mean-field theory were estimated. Obtained
values of Tc and its increase going from the hexagonal to rhombohedral crystal
structure of Gd2Fe17 agree well with experiment. Also for both structures
LSDA+U computed values of total magnetic moment coincide with experimental
ones.Comment: 20 pages, 2 figures; V2 as published in PR
Spatial structure of absorbing vapor in a transversely heated graphite atomizer with a probe
The dynamics of the spatial structure of absorbing layers of silver atoms and molecules and condensed particles of sodium chloride and potassium sulfate in a transversely heated graphite atomizer during atomization of these substances from a platform and evaporation of their condensate from a tungsten probe is investigated by shadow spectral visualization. The fractional probe atomization significantly decreases the spatial inhomogeneities of absorbing layers, the level of nonselective absorption, and the suppression of atomic absorption. As a result, the photometric error decreases. The use of a probe made it possible to increase the maximum amounts of sodium chloride and potassium sulfate allowable for interference-free atomic absorption analysis in a silver sample from 100 to 4000 μg and from 20 to 750 μg, respectively. These values exceed by a factor of 5-8 the acceptable levels in the generally accepted procedure of atomization from a platform with the Pd-Mg modifier. © Nauka/Interperiodica 2006
Some questions of teaching scientific speech to philologist students
В статье рассматриваются некоторые проблемные вопросы обучения иностранных студентов-филологов научной речи, в том числе подготовки и написания выпускной квалификационной работы.The article discusses some problematic issues of teaching foreign studentsphilologists of scientific speech, including the preparation and writing of the final qualifying work
Dynamics of fractional condensation of a substance on a probe for spectral analysis
The fractional separation of trace metals on a cold tungsten probe from salt matrix vapor, which interferes with the spectral analysis, is studied. The spatial structure of the vapor flows of sodium chloride, potassium sulfate, and indium atoms is visualized at characteristic wavelengths as they interact with the probe. The vapor flow rate and the probe orientation were varied. It is found that the smoke of the matrix does not prevent the deposition of the metal on the probe because of spatial separation of these fractions and that the detrimental effect of thermal gas expansion and other factors is eliminated. The sensitivity of the atomic absorption analysis of indium impurities in these salts is increased by an order of magnitude. © 2008 Pleiades Publishing, Ltd
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