2,763 research outputs found
Structural, electronic and elastic properties of RERu2 (RE = Pr, Nd and Sm) Laves phase compounds
Bonding nature, structural, electronic, magnetic and elastic properties of RERu2 (RE = Pr, Nd and Sm) Laves phase compounds have been studied using the full-potential linearized augmented plane wave (FP-LAPW) method based on density functional theory. The LSDA and LSDA+U approach has been used to get accurate results because of the presence of the highly localized 4f electron of RE (RE = Pr, Nd and Sm) atoms. The calculated lattice parameters and magnetic moments are in good agreement with available experimental results. The electronic and bonding properties have been resolved in terms of band structures, DOS, Fermi surfaces and charge density difference plots, which confirm their metallic character. From the charge density difference plots it has been observed that these compounds show mixed covalent-ionic bonding nature simultaneously and metallic bonding is also present. The mechanical properties and Debye temperature have been predicted from the calculated elastic constants. The ductility of these Laves phase compounds have been predicted in accordance with Pugh’s criteria
Fluid-fluid phase separation in hard spheres with a bimodal size distribution
The effect of polydispersity on the phase behaviour of hard spheres is
examined using a moment projection method. It is found that the
Boublik-Mansoori-Carnahan-Starling-Leland equation of state shows a spinodal
instability for a bimodal distribution if the large spheres are sufficiently
polydisperse, and if there is sufficient disparity in mean size between the
small and large spheres. The spinodal instability direction points to the
appearance of a very dense phase of large spheres.Comment: 7 pages, 3 figures, moderately REVISED following referees' comments
(original was 4 pages, 3 postscript figures
Dynamics of diluted magnetic semiconductors from atomistic spin dynamics simulations: Mn doped GaAs as a case study
The dynamical behavior of the magnetism of diluted magnetic semiconductors
(DMS) has been investigated by means of atomistic spin dynamics simulations.
The conclusions drawn from the study are argued to be general for DMS systems
in the low concentration limit, although all simulations are done for 5%
Mn-doped GaAs with various concentrations of As antisite defects. The
magnetization curve, , and the Curie temperature have been
calculated, and are found to be in good correspondence to results from Monte
Carlo simulations and experiments. Furthermore, equilibrium and non-equilibrium
behavior of the magnetic pair correlation function have been extracted. The
dynamics of DMS systems reveals a substantial short ranged magnetic order even
at temperatures at or above the ordering temperature, with a non-vanishing pair
correlation function extending up to several atomic shells. For the high As
antisite concentrations the simulations show a short ranged anti-ferromagnetic
coupling, and a weakened long ranged ferromagnetic coupling. For sufficiently
large concentrations we do not observe any long ranged ferromagnetic
correlation. A typical dynamical response shows that starting from a random
orientation of moments, the spin-correlation develops very fast ( 1ps)
extending up to 15 atomic shells. Above 10 ps in the simulations, the
pair correlation is observed to extend over some 40 atomic shells. The
autocorrelation function has been calculated and compared with ferromagnets
like bcc Fe and spin-glass materials. We find no evidence in our simulations
for a spin-glass behaviour, for any concentration of As antisites. Instead the
magnetic response is better described as slow dynamics, at least when compared
to that of a regular ferromagnet like bcc Fe.Comment: 24 pages, 15 figure
First-principles calculations of exchange interactions, spin waves, and temperature dependence of magnetization in inverse-Heusler-based spin gapless semiconductors
Employing first principles electronic structure calculations in conjunction
with the frozen-magnon method we calculate exchange interactions, spin-wave
dispersion, and spin-wave stiffness constants in inverse-Heusler-based spin
gapless semiconductor (SGS) compounds MnCoAl, TiMnAl, CrZnSi,
TiCoSi and TiVAs. We find that their magnetic behavior is similar to
the half-metallic ferromagnetic full-Heusler alloys, i.e., the intersublattice
exchange interactions play an essential role in the formation of the magnetic
ground state and in determining the Curie temperature, . All
compounds, except TiCoSi possess a ferrimagnetic ground state. Due to the
finite energy gap in one spin channel, the exchange interactions decay sharply
with the distance, and hence magnetism of these SGSs can be described
considering only nearest and next-nearest neighbor exchange interactions. The
calculated spin-wave dispersion curves are typical for ferrimagnets and
ferromagnets. The spin-wave stiffness constants turn out to be larger than
those of the elementary 3-ferromagnets. Calculated exchange parameters are
used as input to determine the temperature dependence of the magnetization and
of the SGSs. We find that the of all compounds is
much above the room temperature. The calculated magnetization curve for
MnCoAl as well as the Curie temperature are in very good agreement with
available experimental data. The present study is expected to pave the way for
a deeper understanding of the magnetic properties of the inverse-Heusler-based
SGSs and enhance the interest in these materials for application in spintronic
and magnetoelectronic devices.Comment: Accepted for publ;ication in Physical Review
Excited hadrons as a signal for quark-gluon plasma formation
At the quark-hadron transition, when quarks get confined to hadrons, certain
orbitally excited states, namely those which have excitation energies above the
respective states of the same order as the transition temperature
, may form easily because of thermal velocities of quarks at the
transition temperature. We propose that the ratio of multiplicities of such
excited states to the respective states can serve as an almost model
independent signal for the quark-gluon plasma formation in relativistic
heavy-ion collisions. For example, the ratio of multiplicities of
and when plotted
with respect to the center of mass energy of the collision (or vs.
centrality/number of participants), should show a jump at the value of
beyond which the QGP formation occurs. This should happen
irrespective of the shape of the overall plot of vs. . Recent
data from RHIC on vs. N for large values of
N may be indicative of such a behavior, though there are large error
bars. We give a list of several other such candidate hadronic states.Comment: 19 pages, RevTex, no figures, minor change
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