Results 1 - 10 of 12
Results 1 - 10 of 12. Search took: 0.018 seconds
|Sort by: date | relevance|
[en] The kinetics of the semi-infinite Ising model in the presence of a time-dependent oscillating external field is studied within the framework of the mean-field approach. We use the Glauber-type stochastic dynamics to describe the evolution time of this system. We present a variety of phase in a semi-infinite cubic ferromagnet with spin-1 in two different, planes; phase diagrams contain (BF, S 1P, SP) phase, (BF, S 1F, SP) phase, completely ordered phase (BF, S 1F, SF) and completely disordered phase (BP, S 1P, SP), which strongly depend on interaction parameters. The nature first and second orders of the transitions is characterized by studying the thermal behaviors of the dynamic magnetizations. Furthermore, the system exhibits dynamical tricritical phenomenon and the reentrant behaviors. The magnetizations and phase space trajectories are given and discussed.
[en] The effects of two different single-ion anisotropies on the magnetization of the mixed (7/2, 5/2) Ising ferrimagnetic system on a square lattice are investigated by the use of Monte Carlo simulation. The ground-state phase diagram is obtained. Compensation points are detected for certain values of the crystal fields. Different types of magnetization curves are available.
[en] Using ab intio numerical calculations based on the all-electron full-potential local-orbital minimum-basis scheme FPLO9.00-34, we discuss the interdistance effect on the energy gap of two parallel layers of the silicone systems. The like- bilayer systems we dealt with here are relying on a dynamic monolayer of silicene located at distance d along the normal direction z forming with a static one a (AA) stacking arrangement. In particular, we investigate the effect of the dynamic layer by varying the distance d starting from a distance around the bond length of Van der Waals. More precisely, we consider the flat and two buckled geometries in (AA) arrangements. The flat geometry is associated with the usual (AA) configuration appearing in the pure graphene material. For buckled geometry, we can distinguish two configurations. The first one corresponds to the usual buckled configuration that keeps the same vertical distance between the two layers atoms while the remaining one is obtained by reversing one silicene layer. We show that the band gap can be opened by simply varying the distance, starting around a Van der Waals distance, between two parallel silicene for flat and buckled geometries due to an electronic transition of electrons living in pz orbital states. Furthermore, we study the stability between the buckled and the flat configuration in the mono and bilayer system.
[en] In this work, we have studied the electronic, electrical and optical properties of HoMn2O5 using first-principles density functional theory within the generalized gradient approximation (GGA). The electrical conductivity decreases with increasing temperature and it exhibits metal-like behavior. The maximum conductivity values as a function of relaxation time reach 11,44.1022 (Q-1m-1s-1) at 300 K. The optical calculation presents this material a good absorbing light in the visible region which is good for many optoelectronic and photovoltaic applications. (paper)
[en] By means of the Monte Carlo method, we have simulated the mixed-spin-1/2 and spin-2 Ising ferrimagnetic system on a honeycomb lattice. We studied the variations of the magnetization as functions of the crystal field and the temperature and obtained the phase diagram of the system for various crystal field values. We have found that the system cannot display a point of compensation if we consider only nearest-neighbor interactions and the crystal field effect. Also, the tricritical point does not exist. To the best of our knowledge, this system has never been studied using the Monte Carlo method.
[en] The structural and electronic properties of the monolayer and bilayer stanene structures have been studied using first-principles calculations. For the monolayer, the buckled structure is more stable than the flat one, with an opening of the band gap when spin-orbit coupling is taken into account, as mentioned in recent studies. For the bilayer, three types of stacking are considered: parallel layers, anti-parallel layers, and parallel layers where the first layer is shifted from the second one. These three configurations are named AA1, AA2, and AB, respectively. The two layers are separated by the distance d. The interactions between two layers of stanene are strong for a short distance, while the van der Waals bonding appears for a longer distance. Furthermore, stanene was fabricated experimentally on a substrate; thus, we proposed another study of electronic properties of stanene deposited on Ge(111) to reveal other behavior as a topological insulator and show the existence of the quantum spin Hall effect.
[en] The effects of single-ion anisotropies and an external magnetic field on the magnetization of the mixed-spin (7/2, 3/2) ferrimagnetic Ising system are investigated within Monte Carlo simulation. Under certain values of the physical parameters, multiple hysteresis loop behaviors such as double, triple, and quintuple hysteresis cycles have been observed. Particularly, the superparamagnetic phase has been shown. The ground-state phase diagrams are presented.
[en] The double perovskite Sr2CrReO6 has very important characteristics for spintronic applications. It is a ferrimagnetic material distinguished by its high Curie temperature Tc≈635 K. We made this statistical study to further reveal the different ways in which this compound can behave with respect to interaction couplings and crystal fields prevailing in the system. We used as approximation an effective field theory (EFT) without correlation in the context of the Ising model. Thus we report different phase diagrams, firstly in relation to the exchange couplings present in the model adopted, and secondly in relation to the crystal fields of Cr and Re. We compare the results found by this method with those found by other statistical methods. Several phase transitions are detected and reentrant phenomenon was observed. - Highlights: • Phase diagram of double perovskite Sr2CrReO6 has been investigated • The phase diagrams depend on the exchange couplings and the crystal fields • Reentrant phenomenon has been observed
[en] The effect of random crystal field on the stationary states of the kinetic spin-1 and spin-3/2 Blume-Capel model is investigated within the framework of the mean field approach. The Glauber-type stochastic dynamics is used to describe the time evolution of the system which is subjected to a time-dependent oscillating external magnetic field. The model exhibits first- and second-order transitions as well as dynamical tricritical, triple and an isolated critical end points. We found that the system displays reentrant phenomenon for both α = 0 and α > 0. Moreover, the system exhibits in the phase space a fixed points and limit cycles with circle, elliptic and parallelogram shapes.
[en] Novel spinel neodymium-tin ferrite nanoparticles (Nd0.5Sn0.5Fe2O4) have been synthesized by the coprecipitation method; x-ray diffraction (XRD), transmission electron microscopy (TEM), and superconducting quantum interference device magnetometer (SQUID) techniques were used to characterize the crystal structure, morphology, and magnetic properties. The spinel structure of a single phase is obtained according to XRD results. From TEM characterization results, we obtained a spherical morphology with an average of 13 nm. Magnetic measurement indicates that the nanoparticles have a superparamagnetic phase with a corresponding blocking temperature (TB) of about 360 K. These new nanomaterials can potentially be used in nanoelectronic devices, magnetic sensors, and hyperthermia application.