101 research outputs found
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
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
Wetting of an Ising system with perfect and corrugated surfaces in a transverse field
Using the mean field theory, a comparative study of the wetting and layering transitions of a spin-1/2 Ising model with perfect and corrugated surfaces, is established. The phase diagrams are investigated and compared in the presence of both a longitudinal and surface fields. The effect of both the temperature and the transverse field on the wetting and layering transitions are established.Using the mean field theory, a comparative study of the wetting and layering transitions of a spin-1/2 Ising model with perfect and corrugated surfaces, is established. The phase diagrams are investigated and compared in the presence of both a longitudinal and surface fields. The effect of both the temperature and the transverse field on the wetting and layering transitions are established
Thermoelectric Properties of Mg doped Mercury Selenide HgSe
Using the density functional theory (DFT) in combination with Boltzmann
transport theory, the influence of Mg concentrations (x) doping on the
thermoelectric properties of Hg1-xMgxSe ternary alloys was systematically
investigated. The generalized gradient approximations of Perdew-Burke-Ernzerhof
(GGA-PBE) have been used to illustrate the exchange correlation potential.
Various thermoelectric transport parameters, such as the Seebeck coefficient
(S), the thermal conductivity over relaxation time, the electrical conductivity
over relaxation time, the power factor (PF) and the figure of merit (ZT) have
been deduced and discussed. The obtained results of thermoelectric properties
show that the studied materials can be useful for room temperature
thermoelectric devices. It is also found that Mg compositions can increase the
thermal efficiency of the HgSe alloy
Ab-initio and Critical behaviors of the perovskite CaMnO for solar cell applications
In this work, we used the density functional calculation (DFT) implemented in
the Quantum Espresso software, using the approximations (GGA, GGA+U) to
illustrate the electronic and magnetic properties of the perovskite CaMnO.
It has been found that the CaMnO perovskite is stable in the G-AFM phase.
When expecting the total and partial DOSs, a strong contribution of the d-Mn
states has been outlined. The Coulomb correction U and the site exchange
interaction J have been implemented and then we compared the two approximations
GGA and GGA+U. It is found that the GGA+U method leads to more accurate results
since this correction takes into account the bonding effects between different
atoms. To complete this study we performed the simulations under Monte Carlo
code based on the Metropolis algorithm. In fact, we have simulated the physical
quantities: magnetization, susceptibility, and specific heat of the studied
CaMnO material as a function of temperature
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