145 research outputs found
Monte Carlo Study of Order-Disorder Layering Transitions in the Blume-Capel Model
The order-disorder layering transitions, of the Blume-Capel model, are
studied using the Monte Carlo (MC) simulations, in the presence of a variable
crystal field. For a very low temperature, the results are in good agreement
with the ground state study. The first order transition line, found for low
temperatures, is connected to the second order transition line, seen for higher
temperatures, by a tri-critical point, for each layer. The reentrant phenomena,
caused by a competition of thermal fluctuations and an inductor magnetic field
created by the deeper layers, is found for the first layers from the
surface, where is exactly the number of layering transitions allowed by
the ground state study. The layer magnetizations , the magnetic
susceptibilities and the quadrupolar magnetic susceptibilities
and the corresponding critical exponent, for each layer , are
also investigated.Comment: 10 pages Latex, 9 figures Postscript forma
Order-disorder layering transitions of a spin-1 Ising model in a variable crystal field
The magnetic order-disorder layering transitions of a spin-1 Ising model are
investigated, under the effect of a variable surface crystal field
, using the mean field theory. Each layer , of the film formed
with layers, disorders at a finite surface crystal field distributed
according to the law , and
being a positive constant. We have established the temperature-crystal field
phase diagrams and found a constant tricritical point and a reentrant
phenomenon for the first layers. This reentrant phenomenon is absent for
the remaining layers, but the tricritical points subsist and depend
not only on the film thickness but also on the exponent . On the other
hand, the thermal behaviour of the surface magnetisation for a fixed value of
the surface crystal field and selected values of the parameter
are established.Comment: 10 Pages Latex, 9 Figures Postscript. To appear in JMMM (2002
A Monte Carlo study of random surface field effect on layering transitions
The effect of a random surface field, within the bimodal distribution, on the
layering transitions in a spin-1/2 Ising thin film is investigated, using Monte
Carlo simulations. It is found that the layering transitions depend strongly on
the concentration of the disorder of the surface magnetic field, for a
fixed temperature, surface and external magnetic fields. Indeed, the critical
concentration at which the magnetisation of each layer changes the
sign discontinuously, decreases for increasing the applied surface magnetic
field, for fixed values of the temperature and the external magnetic field
. Moreover, the behaviour of the layer magnetisations as well as the
distribution of positive and negative spins in each layer, are also established
for specific values of , , and the temperature . \\Comment: 5 pages latex, 6 figures postscrip
Edge wetting of an Ising three-dimensional system
The effect of edge on wetting and layering transitions of a three-dimensional
spin-1/2 Ising model is investigated, in the presence of longitudinal and
surface magnetic fields, using mean field (MF) theory and Monte Carlo (MC)
simulations. For T=0, the ground state phase diagram shows that there exist
only three allowed transitions, namely: surface and bulk transition, surface
transition and bulk transition. However, there exist a surface intra-layering
temperature , above which the surface and the intra-layering surface
transitions occur. While the bulk layering and intra-layering transitions
appear above an other finite temperature . These
surface and bulk intra-layering transitions are not seen in the perfect
surfaces case.
Numerical values of and , computed by Monte Carlo
method are found to be smaller than those obtained using mean field theory.
However, the results predicted by the two methods become similar, and are
exactly those given by the ground state phase diagram, for very low
temperatures. On the other hand, the behavior of the local magnetizations as a
function of the external magnetic field, shows that the transitions are of the
first order type. and decrease when increasing the
system size and/or the surface magnetic field. In particular,
reaches the wetting temperature for sufficiently large system sizes.Comment: 11 Pages latex, 12 Figures P
Study of the Physical Properties of the EuCoAAs Compound: A DFT approach
In this study, we carried out an investigation of the EuCoAAs
compound, focusing on its various physical properties. Our analysis covered the
structural, magnetic, electronic, optical, thermodynamic and thermoelectric
characteristics of this compound. To carry out this study, we used density
functional theory (DFT) implemented in the Wien2k software package. To
determine the exchange-correlation potential, we used the GGA-PBE (Perdew,
Burke and Ernzerhof) approach, taking spin-orbit coupling (SOC) into account.
Our results indicate that the EuCoAAs compound exhibits metallic
behavior. In addition, we have determined that the compound's stable ground
state is the ferromagnetic (FM) phase. We have also calculated the Debye
temperature and the Gr\"uneisen parameter. In addition, we evaluated various
optical properties, including electron energy loss, absorption coefficient,
real and imaginary dielectric tensors, and real and imaginary optical
conductivity. We found that the compound has excellent absorption
characteristics in the low and mid ultraviolet (UV) spectra. In addition, we
investigated the electrical conductivity, Seebeck coefficient, electronic
conductivity and thermal conductivity of the lattice. The results revealed that
the compound exhibits n-type behavior, with negative values for the Seebeck
coefficient. These results are analyzed in detail and provide valuable
information on the properties of the EuCoAAs compound. Additionally,
the computed parameters were compared to those found in the literature. A good
deals have been revealed with the existing results.Comment: 26 pages, 7 figures, 3 table
Structural, electronic, and magnetic properties of ZnTe doped with transition metal Mn
In this article, we examine the structure and the electronic, optical, and
magnetic properties of ZnTe before and after doping with the transition metal
Mn. The ab initio calculations of this compound were performed using the full
potential linearized extended full potential planar waveform (FP-LAPW) in the
context of density functional theory (DFT) implemented in the Wien2K code. The
potential for exchange and correlation was addressed by the generalized
gradient approximation (GGA) approximation. The electronic properties show that
the ZnTe material exhibits semiconductor behavior before doping. As a result,
it becomes semimetal after doping. The findings attained by Monte Carlo
simulations display that the ZnMnTe material goes from an antiferromagnetic
phase to the paramagnetic phase at the Neel temperature value TN =159.31 K
Study of Physical Characteristics of the New Half-Heusler Alloy BaHgSn by DFT Analysis
To investigate the physical characteristics of the half-Heusler BaHgSn
molecule, we used theoretical calculations within the Density Functional Theory
(DFT) framework utilizing the LSDA+mBJ technique in this study. Using the
optimal lattice parameters, we discover that half-Heusler BaHgSn exhibits a
Dirac semimetal behavior with a band gap of 0.1 eV. Thomas Charpin's numerical
first-principles calculation approach was applied to determine the elastic
constants of hexagonal BaHgSn alloys. The material's optical characteristics
verified its prospective use in infrared-visible devices. According to a
thermo-electric properties analysis, at 20x10^18 {\Omega}-1.m-1.s-1, the
electrical conductivity reaches its maximum after increasing gradually up to
500 K. Compared to other compounds, these results indicate that BaHgSn has
potential for use in opto-electronic and thermo-electric devices
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