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 $p$ of the disorder of the surface magnetic field, for a fixed temperature, surface and external magnetic fields. Indeed, the critical concentration $p_c(k)$ at which the magnetisation of each layer $k$ changes the sign discontinuously, decreases for increasing the applied surface magnetic field, for fixed values of the temperature $T$ and the external magnetic field $H$. 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 $H_s$, $H$, $p$ and the temperature $T$. \\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 $T_{L}^{s}$, 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 $T_{L}^{b} (\ge T_{L}^{s})$. These surface and bulk intra-layering transitions are not seen in the perfect surfaces case. Numerical values of $T_{L}^{s}$ and $T_{L}^{b}$, 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. $T_{L}^{s}$ and $T_{L}^{b}$ decrease when increasing the system size and/or the surface magnetic field. In particular, $T_{L}^{b}$ reaches the wetting temperature $T_{w}$ for sufficiently large system sizes.Comment: 11 Pages latex, 12 Figures P

Study of the Physical Properties of the EuCoA2_2As2_2 Compound: A DFT approach

In this study, we carried out an investigation of the EuCoA$_2$As$_2$ 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 EuCoA$_2$As$_2$ 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 EuCoA$_2$As$_2$ 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