Search

By using the effective field theory (EFT), the mixed spin-1/2 and spin-3/2 Ising ferrimagnetic model adapted to a double perovskite structure has been studied. The EFT calculations have been carried out from Ising Hamiltonian by taking into account first and second nearest-neighbors interactions and the crystal and external magnetic fields. Both first- and second-order phase transitions have been found in phase diagrams of interest. Depending on crystal-field values, the thermodynamic behavior of total magnetization indicated the compensation phenomenon existence. The hysteresis behaviors are studied by investigating the reduced magnetic field dependence of total magnetization and a series of hysteresis loops are shown for different reduced temperatures around the critical one. [ABSTRACT FROM AUTHOR]

Abstract: We study the influence of the surface of the ferroelectric films on the properties of the intrinsic ferroelectric polarization state in frame of statistical Transverse Ising Model (TIM). The quality of the surface is modelled by the dilution parameter that reflects the relative weight of the paraelectric impurities vs. ferroelectric ions. Using the effective field approach the variation of the average value of spontaneous polarization as function of temperature for different film thicknesses has been investigated as function of dilution parameter . The phase diagram of the system and crossover from the ferroelectric to the paraelectric phase is discussed. [Copyright &y& Elsevier]

The influence of a non-perfect surface on the critical properties of magnetic spin-1/2 Ising film on a cubic lattice structure is studied using Monte Carlo simulations based on Metropolis algorithm. The surface magnetization and the surface effective exponent have been studied for several concentration p. Far from the critical temperature, the surface effective exponent βeffs decreases with increasing the concentration p. [ABSTRACT FROM AUTHOR]

Using Monte Carlo simulation with the Metropolis algorithm, we have studied the critical behaviour of magnetic spin 1/2 Ising film on a cubic lattice structure. We drive the effective exponent of the each layer βeff(z,t) and of the film βefff (t) as a function of reduced temperature t. A particular attention is paid for the evaluation of the variation of the critical exponents with the film thickness. [ABSTRACT FROM AUTHOR]

Abstract: Using Monte Carlo simulations with the Metropolis algorithm, we have studied the influence of crystal-field interaction on the critical behavior of magnetic spin-1 Ising film on a cubic lattice structure. The phase diagrams in the plane are obtained for different values of the crystal-field interaction. We found that the special point , at which the critical temperature is independent of the film thickness N, is independent of the crystal-field interaction and that the system may exhibit a tricritical behavior. [Copyright &y& Elsevier]

Within an effective field theory we investigate the anisotropy of an antiferromagnetic coupling and the Ne´el temperature in a diluted spin-7/2 Ising model. The bond dilution (p) effect in the Ne´el temperature is shown in (TN,p) plane for some selected values of anisotropic parameter αc=Jc/J. The temperature dependence of the magnetic moment has been studied for some values of p and αc. [Copyright &y& Elsevier]

Using Monte Carlo simulations, magnetic properties of the ferromagnetic nanoparticles of Ising spin-1 are investigated in the framework of the Ising model. The system is considered to have a Rubik’s cube structure composed of nanocubes having an equivalent exchange coupling, while, between adjacent nanocubes, the exchange coupling is assumed to vary. Both size effects and system parameters’ influence on phase diagrams of the nanosystem are studied. Thus, the magnetic properties of the system such as the critical temperature, the magnetization, and the coercive field are computed. [ABSTRACT FROM AUTHOR]

The multi-component Ising-like network model on x-y rectangular lattice was developed to describe the ferroelectric phase transition in Tetragonal Tungsten Bronze (TTB) compounds. Using Monte Carlo simulation with Metropolis algorithm we reproduced the phase diagram of this model as a function of the temperature and exchange interaction and demonstrated it coherence with experimental data. [ABSTRACT FROM AUTHOR]

Abstract: Monte Carlo simulation has been used to study the magnetic properties and hysteresis loops of a single nanocube, consisting of a ferromagnetic core of spin- surrounded by a ferromagnetic shell of spin-1 with antiferromagnetic interface coupling. We find a number of characteristic phenomena. In particular, the effects of the shell coupling and the interface coupling on both the compensation temperature and the magnetization profiles are investigated. The effects of the interface coupling on the hysteresis loops are also examined. [Copyright &y& Elsevier]

Glass-ceramics in the system xBaTiO3-(1-x)NaPO3 (0 ≤ x ≤ 14, x in mol%) have been prepared and characterized. The structural organization of the glass-ceramics has been studied using XRD diffraction and infra-red (FTIR), 31P Magic angle spinning (MAS-NMR) and dielectric spectroscopies. Results suggest two distinct regions comprising the glass structure, one with low-BaTiO3 content and the other with higher content of the ferroelectric compound BaTiO3. The depolymerisation effects and the structure changes, promoted by BaTiO3 addition, are evidenced by means of the IR and NMR results. Dielectric permittivity shows that the ferroelectric-paraelectric transition temperature of each glass-ceramic appears at the same temperature for a pure BaTiO3 ceramic. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to evaluate the physical properties of Fe 3 S 4 material. To do so, Ab-initio calculations and Monte Carlo Simulations (MCS) by means of the mixed spin model have been used. Fe 3 S 4 compound is formed by two magnetic sub-lattices, one occupied the A tetrahedral with spin 5/2 and the other occupied by B octahedral with both spin 2 and 5/2. The density of states (DOS) has been investigated and confirmed that the compoundis a half metal. Further, the magnetization, susceptibility and specific heat curves have been determined for different sizes of the systemand fromwhich the values of critical exponentsand the critical temperature (T c) have been calculated. Besides, the temperature-dependent magnetization for different values of crystal field has been analyzed to provide an insight into the relation compensation phenomena and crystal field effect. [ABSTRACT FROM AUTHOR]

We aim in this research paper to investigate and determine the magnetic properties of the simple perovskite PbVO by determining all the stable phases and analyzing and discussing the ground phase diagrams as a first step. As the second one, we established the magnetic properties of the studied compound employing a Monte Carlo simulation method within the framework of the Ising model to further the investigation. As a result of the employment of MCS, we succeed to determine the critical temperature, which is deduced by studying the magnetization, the susceptibility, and the specific heat. Then, comparing the previous experimental results with our theoretical obtained results, we found a good agreement between them. Also, the coupling effect on the transition temperature was shown. Finally, we analyzed the critical behaviors. [ABSTRACT FROM AUTHOR]

Using Monte Carlo simulations, we studied phase diagrams and magnetic properties of a ferromagnetic/antiferromagnetic Ising nanoparticles assembly with the spin-1/2 core and spin-3/2 shell. The system consists of nanocubes with equivalent exchange couplings of core and shell. However, the exchange couplings between the adjacent spins of the core and shell and between the nanocubes are assumed to vary. Thus, the effects of the exchange couplings and the system size on the phase diagrams are analyzing. Interesting behaviors are found when investigating the critical behavior of the system, the magnetizations, the magnetic susceptibility and the hysteresis loops. The increase of the core/shell size involves that of the temperature one. In addition, the increase in positive exchange interactions between the spins of the core and shell, on the one hand, and between the nanocubes, on the other hand, also increase the critical temperature, which favors the stable phase (3/2, 1/2). • Monte Carlo Simulation is used to study the magnetic properties of an assembly of cubic Core-Shell nanoparticles. • Phases diagrams of critical temperature with the exchange interactions and anisotropy parameter have been studied. • The increase of positive J2/J1 and J4/J1 increase the critical temperature, favoring the stable phase (3/2, 1/2). • Core and Shell sizes, anisotropy and interactions parameters effects on Magnetic hysteresis cycles are given. • Dependent coercivity with sizes and parameters of interactions are found. [ABSTRACT FROM AUTHOR]

In this paper, the electronic, structural, and magnetic properties of transition metal (TM) (V, Cr, Mn, Fe, Co, Ni, Cu)-doped CdSe are investigated using first-principles calculations within the density functional theory (DFT) and the local density approximation (LDA) in connection with the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) implemented in the AKAI MACHIKANEAMA code. The 3 d level locations of majority spin of those magnetic ions are studied. The spin-spin interaction at low concentration between magnetic impurities leads to ferromagnetic behavior. While the increase of TM concentration beyond 10 % leads to antiferromagnetic interactions between the magnetic ions, which suppress the ferromagnetism. Magnetic stability and Curie temperature are also calculated for different TM doping. And finally, two TMs are chosen to make a codoping in CdSe semiconductor material. [ABSTRACT FROM AUTHOR]

Abstract: Using Monte Carlo simulations, we have studied the influence of surface defects on the critical behavior of magnetic spin- Ising film on a cubic lattice structure. We derive the phase diagram and the critical exponent β in the case of a perfect surface. In such films, the critical temperature can shift to either lower or higher values compared to the corresponding bulk one. In the case of a surface with random, ‘weak’ or ‘strong’ interactions between neighboring spins, it is found that the critical exponent β 1 follows very closely that of the perfect surface case. Far from the critical temperature, the effective exponent decreases with increasing the concentration of strong interactions p. [Copyright &y& Elsevier]

Abstract: In microscale and nanoscale ferroelectric samples, the formation and growth of domains are the usual stages of the polarization switching mechanism. By assuming weak polarization anisotropy and by solving the Ginzburg–Landau–Khalatnikov equation we have explored an alternative mechanism which consists in ferroelectric switching induced by vortex formation. We have studied the polarization dynamics inside a ferroelectric circular capacitor where switching leads to the formation of a metastable vortex state with a rotational motion of the polarization. Our results are consistent with recent first-principle simulations [I.I. Naumov, H.X. Fu, Phys. Rev. Lett. 98, 077603 (2007)] and with experiments on PbZr0.2Ti0.8O3 [A. Gruverman, D. Wu, H.J. Fan, I. Vrejoiu, M. Alexe, R.J. Harrison, J.F. Scott, J. Phys. Condens. Matter 20 342201(2008)] and demonstrate that vortex-induced polarization switching can be an effective mechanism for circular nanocapacitors. [Copyright &y& Elsevier]

Abstract: The present study concerns the system 0.5[xNa2O–(1− x)Li2O]–0.5[0.4(MoO3)2–0.6P2O5], with x varying between 0 and 1. The elaborated glass samples have been characterised using powder X-ray diffraction (XRD), differential thermal analysis (DTA) and impedance spectroscopy. The total alkali oxide content is chosen in order to ensure that the electrical conductivity of the glasses under study is entirely ionic. It was evidenced that the conductivity minimum corresponds to the maximum of the activation energy. The glass transition temperature seems to present a minimum for the ratio Na/(Na+Li)=0.5. On the other hand, the density appears very linearly versus Na/(Na+Li). The mixed alkali effect (MAE) is resulting here in a conductivity minimum observed for the composition corresponding to Na/(Na+Li)=0.5, (x =0.5). It could be attributed to the fact that the two types of alkali ions are randomly mixed and have distinct conduction pathways. This implies that Li ions tend to block the pathways for the Na ions and vice versa. [Copyright &y& Elsevier]

Samples of zelliges, from the Dar-El Beïda Palace built in Meknes (Morocco) in the 18th century, were studied by optical absorption and Raman spectroscopies. The results obtained by the two techniques were in agreement and show that the glazes of the zelliges are lead oxide-rich in composition. Other phases were also detected, mainly the SnO2 cassiterite opacifier for the white glaze, and heamatite (α-Fe2O3) in association with magnetite Fe3O4 and manganese oxide (MnO2) for the brown glaze. For the blue and green glazes, the elements responsible for the coloring are cobalt (Co2+) and copper (Cu2+), respectively. [ABSTRACT FROM AUTHOR]

Glasses belonging to the series yA2O-(1-y)[0.25(WO3)2-0.75P2O5] ( y=0.10-0.60) are elaborated. DTA experiments reveal that the glass-network of the glasses are broken with increasing of modifier content. EPR spectra show the presence of two signals due to W5+ and Mo5+, as impuritie. The intensity of these EPR centres decreases when the concentration of A2O increases. The variation of Tg upon the modifier content is ascribed to structural changes occurring in the matrix of these glasses. [ABSTRACT FROM AUTHOR]