Growth of homopolymer chain

Thermodynamic and kinetic properties of an homopolymer chain, in two dimensional square lattice, are studied by the use of chain growth algorithm based on the self avoiding walks process. Which is in accord with what happen in nature. All monomers are considered to be hydrophobic. In the thermodynamical study we examine the critical behaviour of the chain by following the evolution of the chain geometry with temperature. This is done by studying the behaviour of the mean distance R chosen to describe the homopolymer structure. Moreover, we give the behaviour of thermodynamic quantities such as conformational energy and specific heat. The effect of a force applied, in a fixed direction, on the chain when it is growing is also investigated. Finally, in a kinetic study, we analyse the evolution with temperature of the mean time necessarily for a given conformation to reach its native state.Thermodynamic and kinetic properties of an homopolymer chain, in two dimensional square lattice, are studied by the use of chain growth algorithm based on the self avoiding walks process. Which is in accord with what happen in nature. All monomers are considered to be hydrophobic. In the thermodynamical study we examine the critical behaviour of the chain by following the evolution of the chain geometry with temperature. This is done by studying the behaviour of the mean distance R chosen to describe the homopolymer structure. Moreover, we give the behaviour of thermodynamic quantities such as conformational energy and specific heat. The effect of a force applied, in a fixed direction, on the chain when it is growing is also investigated. Finally, in a kinetic study, we analyse the evolution with temperature of the mean time necessarily for a given conformation to reach its native state

Mean field study of decorated ferrimagnetic Ising model

The magnetic properties of a decorated ferrimagnetic Ising model consisting of two magnetic atoms A and B with spins σA= 1/2 and SB=1 are investigated by the use of the mean field approximation. Transition temperatures and the existence of the one or double compensation temperatures of the decorated ferrimagnetic square lattice are examined.The magnetic properties of a decorated ferrimagnetic Ising model consisting of two magnetic atoms A and B with spins σA= 1/2 and SB=1 are investigated by the use of the mean field approximation. Transition temperatures and the existence of the one or double compensation temperatures of the decorated ferrimagnetic square lattice are examined

Magnetic properties of spherical ferri-magnetic core/shells: A Monte Carlo study

In this work, we study the magnetic properties of a spherical ferrimagnetic core/shell, formed with nanoparticles of a spin-1/2 in the core surrounded by spin-1 in the shell layer. An external magnetic field is applied on this system. In addition, we examined the magnetizations as well as the susceptibilities of this system, for specific values of the coupling constants between the spins of the shell-shell Js, the core-shell Jp and core-core Jc. The response of the magnetization to the field is illustrated in the hysteresis loops

The Effect of Vacancy Defect and size on the double perovskite Sr2VMoO6: A Monte Carlo study

In this work, Monte Carlo simulations are performed to study the effect of vacancy defects on magnetic properties of a double perovskite Sr2VMoO6 film. The ions Mo5+ are modelized by  spins, whereas the ions V3+ are represented by S=1 spins. The vacancy concentration and the temperature effects are examined on the behavior of the magnetizations and susceptibilities for several system sizes.  From the obtained results, it is found that the increase of the defect concentration, decreases the magnitude of the magnetization, for a fixed system size. Also, we have studied the influence of an external and crystal fields on the critical behavior. Additionally, the response of the magnetization to the field shows a hysterisis behavior

Random crystal-field effect on magnetic materials

Using the mean field theory, we investigate the effect of the random crystal-field on both the spin-3/2 and spin-2 Blume-Capel models. Several new features are found including the apparence of new ordered phases at low temperature and consequently rich ground state phase diagrams. At finite temperature, new types of phase diagrams are found. Furthermore, we show that at low temperature, first-order transition lines are terminated by isolated critical points, between the ferromagnetic phases. We also discuss some interesting phenomena such as the existence of compensation and the existence of topologically different types of phase diagrams. The magnetic properties and phase diagrams of this model are presented. The obtained results confirm the existence of new ferri-magnetic phases and consequently the existence of new topologies for the different types of the phase diagrams. Indeed, these phase diagrams present rich varieties of phase transitions with first and second order phase transition lines. These lines are found to be linked by tri-critical points and terminated at isolated critical points. In the case of the spin-2 Blume-Capel model, the interesting finding to emerge consists in the appearance of a new phase, with magnetization (m=3/2), and consequently new types of phase diagrams, divided on topologies depending on the existence of the paramagnetic phase at temperature T=0 K. Finally, the thermal behaviour of the sub-lattices magnetizations, showed the presence of the compensation behaviours for negative values of the crystal-field.Using the mean field theory, we investigate the effect of the random crystal-field on both the spin-3/2 and spin-2 Blume-Capel models. Several new features are found including the apparence of new ordered phases at low temperature and consequently rich ground state phase diagrams. At finite temperature, new types of phase diagrams are found. Furthermore, we show that at low temperature, first-order transition lines are terminated by isolated critical points, between the ferromagnetic phases. We also discuss some interesting phenomena such as the existence of compensation and the existence of topologically different types of phase diagrams. The magnetic properties and phase diagrams of this model are presented. The obtained results confirm the existence of new ferri-magnetic phases and consequently the existence of new topologies for the different types of the phase diagrams. Indeed, these phase diagrams present rich varieties of phase transitions with first and second order phase transition lines. These lines are found to be linked by tri-critical points and terminated at isolated critical points. In the case of the spin-2 Blume-Capel model, the interesting finding to emerge consists in the appearance of a new phase, with magnetization (m=3/2), and consequently new types of phase diagrams, divided on topologies depending on the existence of the paramagnetic phase at temperature T=0 K. Finally, the thermal behaviour of the sub-lattices magnetizations, showed the presence of the compensation behaviours for negative values of the crystal-field

XMCD studies and magnetic properties of ZnTe doped with Ti, Cr, Mn and Co

Using the full potential linear augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code in connection with the Generalized Gradient Approximation (GGA). We study the magnetic properties of ZnTe doped with some transition metals elements. In addition, to the X-ray absorption spectra (XAS) and X-ray Magnetic circular dichroism (XMCD) calculations to compute the orbital and spin moments separately. Two principal examples will be given: The induced magnetic moments ZnTe of the light and heavy 3d elements (Ti, Cr and Mn, Co) can be determined by the XMCD sum rules analysis at the L2,3 edges. Moreover, it has been found that for the lighter 3d elements the spin-orbit splitting of the transitions 2P1/2 and 2P3/2 states reduces toward, which has a consequence that two excitations are coupled

Magnetization and ordering temperature of films and multilayers

We investigate, in this paper, a number of magnetic properties of single and multilayer thin film systems within the Ising model by application of mean field, finite cluster approximations as well as by Monte Carlo simulations. The magnetization profiles and the magnetic ordering temperature are calculated for different magnetic systems. The influence of corrugation and disorder at the surface, on the critical behavior of ferromagnetic Ising film is also studied. It is found that the critical surface exponent of the magnetization follows closely the one of a perfect surface, in the two cases: corrugated surface and random equiprobable coupling surface. However, in the case of flat surface with random interactions the surface critical exponent depends on the concentration of the strong interaction, while such critical exponent is independent on the concentration. Moreover, in the case of corrugated surface, the effective exponent for a given layer, is a function of the number of steps at the surface. The probability of a magnetic ground state is larger for low spatial dimensionality of an extended system, or lower for local symmetry of a given site in the atomic lattice. Consequently, the magnetic properties are usually more pronounced at the surface of a bulk magnet as compared to the bulk interior. The phase diagram and the characteristic behaviors of the surface magnetization, are investigated for amorphous or cristalline surfaces. Indeed, the size effects become more relevant at low temperature depending on film thickness.We investigate, in this paper, a number of magnetic properties of single and multilayer thin film systems within the Ising model by application of mean field, finite cluster approximations as well as by Monte Carlo simulations. The magnetization profiles and the magnetic ordering temperature are calculated for different magnetic systems. The influence of corrugation and disorder at the surface, on the critical behavior of ferromagnetic Ising film is also studied. It is found that the critical surface exponent of the magnetization follows closely the one of a perfect surface, in the two cases: corrugated surface and random equiprobable coupling surface. However, in the case of flat surface with random interactions the surface critical exponent depends on the concentration of the strong interaction, while such critical exponent is independent on the concentration. Moreover, in the case of corrugated surface, the effective exponent for a given layer, is a function of the number of steps at the surface. The probability of a magnetic ground state is larger for low spatial dimensionality of an extended system, or lower for local symmetry of a given site in the atomic lattice. Consequently, the magnetic properties are usually more pronounced at the surface of a bulk magnet as compared to the bulk interior. The phase diagram and the characteristic behaviors of the surface magnetization, are investigated for amorphous or cristalline surfaces. Indeed, the size effects become more relevant at low temperature depending on film thickness

Wetting and layering transitions of a spin-1/2 Ising model in a random transverse field method

The effect of a random transverse field (RTF) on the wetting and layering transitions of a spin-1/2 Ising model, in the presence of bulk and surface fields, is studied within an effective field theory by using the differential operator technique. Indeed, the dependencies of the wetting temperature and wetting transverse field on the probability of the presence of a transverse field are established. For specific values of the surface field we show the existence of a critical probability pc above which wetting and layering transitions disappear.The effect of a random transverse field (RTF) on the wetting and layering transitions of a spin-1/2 Ising model, in the presence of bulk and surface fields, is studied within an effective field theory by using the differential operator technique. Indeed, the dependencies of the wetting temperature and wetting transverse field on the probability of the presence of a transverse field are established. For specific values of the surface field we show the existence of a critical probability pc above which wetting and layering transitions disappear

NUMERCAL STUDY OF A FOUR COMPONENTS SYSTEM

We have investigated numerically a statistical model of four component systems, which exhibit two critical temperatures, called the Ashkin-Teller model (ATM). The effects of, the anisotropy coupling, the single ion potential field and the mixed spin on the structure of the phase diagram have been studied. The model presents a rich variety of phase transitions which meet on tricritical or multicritical points. Different partially ordered phases with a partially broken symmetry appears at high temperatures. Their region of stability and their structure depend on the phase parameter space. The nature of critical lines which bound these partially ordered phases depends on the coupling parameters and the crystalline anisotropy".We have investigated numerically a statistical model of four component systems, which exhibit two critical temperatures, called the Ashkin-Teller model (ATM). The effects of, the anisotropy coupling, the single ion potential field and the mixed spin on the structure of the phase diagram have been studied. The model presents a rich variety of phase transitions which meet on tricritical or multicritical points. Different partially ordered phases with a partially broken symmetry appears at high temperatures. Their region of stability and their structure depend on the phase parameter space. The nature of critical lines which bound these partially ordered phases depends on the coupling parameters and the crystalline anisotropy

Numerical study of rice-pile model

A one-dimensional model of a rice-pile is numerically studied for different driving mechanisms. We found that for a sufficiently large system, there is a sharp transition between the trivial behaviour of a 1D BTW model and self-organized critical (SOC) behaviour. Depending on the driving mechanism, the self-organized critical rice-pile model belongs to two different universality classes.A one-dimensional model of a rice-pile is numerically studied for different driving mechanisms. We found that for a sufficiently large system, there is a sharp transition between the trivial behaviour of a 1D BTW model and self-organized critical (SOC) behaviour. Depending on the driving mechanism, the self-organized critical rice-pile model belongs to two different universality classes