Results 1 - 10 of 65
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[en] The influence of frustration on the phase transitions of a semi-infinite three-dimensional Ising model is investigated. Temperature-concentration phase diagrams for fixed values of the ratio of surface and bulk interactions can exhibit five different types of phase transition. (author). 6 refs, 1 fig
[en] Using the finite cluster approximation, phase diagrams of bond and site diluted three-dimensional simple cubic Ising models with a random field have been determined. The resulting phase diagrams have the same general features for both bond and site dilution. (author). 7 refs, 4 figs
[en] The magnetic properties of ferrimagnetic mixed-spin Ising model in the checkerboard lattice are studied using Monte Carlo simulations. The variation of total magnetization and magnetic susceptibility with the crystal field has been established. A transition from an order to a disordered phase has been obtained in some critical value of the physical variables. The reduced transition temperature is obtained for different exchange interactions. The magnetic hysteresis cycles have been established. The multiples hysteresis cycle in checkerboard lattice are obtained. The multiples hysteresis cycle have been established. The ferrimagnetic mixed-spin Ising model in checkerboard lattice is very interesting from the experimental point of view. The mixed spins system have many technological applications such as in domain opto-electronics, memory, nanomedicine and nano-biological systems. The obtained results show that that crystal field induce long-range spin–spin correlations even bellow the reduced transition temperature
[en] The effect of the Dzyaloshinskii-Moriya interaction on the stability of the Neel phase and the energy gap for the XXZ Heisenberg model on a d-dimensional hypercubic lattice is investigated using the linear spin-wave theory. In one-dimension, the disordered phase disappears above a critical value of the spin-axis anisotropy. In two-dimension, the instability of the Neel order occurs below a critical value of the easy-axis anisotropy. We find that for all d-dimensional systems, the energy gap vanishes above a critical value of the DM interaction. (author)
[en] The (1+1)-dimensional Hamiltonian q-state ferromagnetic Potts model in an external magnetic field H is studied using finite lattice extrapolation techniques. The possible phases and their boundaries are determined from the ground state energy and the gap in the excitation energy, for arbitrary values of q and both for positive and negative field. We found that, for H positive, there is a critical value qc, where a first order transition line appears for q>qc, starting at the zero field transition point and terminating at a critical point in (h/λ, H/λ) plane, which separates the disordered phase and the ordered phase in the direction of H. For h negative a critical transition line separating the disordered phase and the others (q-1) ordered phases becomes first order for q>qc. (author). 12 refs, 2 figs
[en] The effects of amorphized film and diluted surface on phase diagrams and magnetic properties of a spin-1/2 Ising film are investigated within a finite cluster approximation. Depending on the value of the concentration p of the dilution couplings at the surface, it is found that there exists a critical value pc, when increasing the thickness of the film the critical temperature Tc decreases for p greater than pc, while it increases for p less than pc. Moreover, the critical concentration depends on the amorphization δ. Indeed, pc increasing with increasing δ. Besides, the phase diagram represented in (Tc,α), where α represents the strength of the strong coupling at the surface, shows that there exists a critical value of the amorphization δc=δc(p) for p not= 1, for δ≤δc(p) a long range order occurs for any value of α at low temperature, while for δ>δc(p) an order-disorder transition occurs at T=0 and α=αc(δ). Magnetization is calculated as a function of the amorphization δ, the concentration p and the strength α of the strong coupling. (author)
[en] The influence of corrugation and disorder at the surface on the critical behaviour of a ferromagnetic spin-1/2 Ising film is investigated using mean-field theory and finite cluster approximation. It is found that the critical surface exponent β1 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 β1 depends on the concentration p of the strong interaction for p>pc=0,5, while for p≤pc, such critical exponent is independent on the value of p and is equal to the one of the perfect surface. Moreover, in the case of corrugated surface, the effective exponent for a layer z, βeffJ(z,n), is calculated as a function of the number of steps at the surface. (author)
[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] Two non perturbative methods by means of the Transfer-Matrix Finite-Size-Scaling (TMFSS) and Monte Carlo (MC) simulations are used to investigate the spin-1 Ashkin-Teller model (A.T.M.). We have obtained rich phase diagrams with first and second order phase transitions with several multicritical points of higher order. Also this model exhibits a new partially ordered phase PO2 which does not exist in the spin-1/2 Ashkin-Teller model (A.T.M.). Finally, the critical behaviour of this model is discussed. (author)
[en] In this paper, we aimed to study the effect of doping of the compound CdTe with the cobalt impurity (Co), as well as the vacancy defects in Cd sites. On one hand, this leads to the investigation of the magnetic properties and the Faraday rotation effect for the studied alloy, doped with different concentrations of cobalt (0.01, 0.05, 0.1, 0.15, 0.2, 0.25). On the other hand, we have created 0.01 of vacancy defects in Cd sites. Then, we raised the vacancy defect concentration to 0.05, keeping the same concentrations of cobalt. As a result, we have investigated that there is a magnetism appearing with the cobalt doping, while the vacancy defects in Cd sites affect the stability of the magnetic states. In general, it improves the ferromagnetic state that will be well explained in the discussion. Our calculations were performed using the KKR-CPA method within the spin-polarized density functional theory (DFT) with the local density approximation (LDA). The curves of the density of states (DOS) illustrate the results of this study which has been discussed, analyzed, and explained below. In addition, the energy of each case was calculated and given in the tables below for both the DLM (half of the cobalt spins are up while the other half are down) and the ferromagnetic state in order to confirm which one of them is stable.