M. Loulidi

Phase diagrams of a ferromagnetic amorphous bilayer system

Abstract Using the effective-field theory, we study phase diagrams of a ferromagnetic amorphous bilayer system, consisting of two monolayers (A and B) with different spins ( S A = 1 2 and S B = 1 2 , 1) and different interaction constants coupled together with an interlayer coupling. The effects of amorphization in the monolayer B and in the interlayer coupling are investigated. The influence of the crystal-field interaction D , in the case S A = 1 2 and S B =1, is also studied. A number of interesting phenomena are obtained such as the dependence of the tricritical behavior on amorphization. Other phenomena have been given in a variety of phase diagrams. The temperature dependence of the total magnetization is also examined.

First principle calculations for improving desorption temperature in Mg16H32 doped with Ca, Sr and Ba elements

Using ab initio calculations, we predict the improvement of the desorption temperature and the hydrogen storage properties of doped Mg-based hydrides such as, Mg15AMH32 (AM = Ca, Sr and Ba) as a super cell 2 × 2 × 2 of MgH2. In particular, the electronic structure has been obtained numerically using the all-electron full-potential local-orbital minimum-basis scheme FPLO9·00-34. Then, we discuss the formation energy calculations in terms of the material stabilities and the hydrogen storage thermodynamic properties improvements. Among others, we find that the stability and the temperature of desorption decrease without reducing significantly the high storage capacity of hydrogen. Moreover, it has been observed that such a doping procedure does not affect the electronic behavior as seen in MgH2, including the insulator state in contrast with the transition metal hydrides, which modify the electronic structure of pure MgH2.

Phase Diagrams and Magnetic Behaviour of Films with Amorphous Surfaces

The phase diagrams and magnetic behaviour of thin films with two amorphized surfaces are investigated by the use of the effective field theory with correlations. The transition temperature dependence of the exchange integral at surfaces, coupling between surface and nearest-layer, film thickness, and structural fluctuations are studied. Some interesting phenomena can occur as wetting phenomenon and compensation point.

Electronic and magnetic structures of V-doped zinc blende Zn 1−x V x N y O 1−y and Zn 1−x V x P y O 1−y

Electronic and magnetic structures of zinc blende ZnO doped with V impurities are studied by first-principles calculations based on the Korringa—Kohn—Rostoker (KKR) method combined with the coherent potential approximation (CPA). Calculations for the substitution of O by N or P are performed and the magnetic moment is found to be sensitive to the N or P content. Furthermore, the system exhibits a half-metallic band structure accompanied by the broadening of vanadium bands. The mechanism responsible for ferromagnetism is also discussed and the stability of the ferromagnetic state compared with that of the paramagnetic state is systematically investigated by calculating the total energy difference between them by using supercell method.

PHASE TRANSITIONS OF THE MIXED-SPIN ISING MODEL ON A DECORATED LATTICE WITH THE NEAREST-NEIGHBOR INTERACTION BETWEEN DECORATING SPINS

A mean-field approximation is developed for a decorated ferrimagnetic Ising model, in which the two magnetic atoms A and B have spins σ=1/2 and S=1, respectively. In this system, the exchange interaction between nearest-neighbors of atom B is taken into account. Some interesting phenomena, such as the appearance of three types of phase diagrams and the existence of one and two compensation points are found. Phase diagrams and temperature dependence of the magnetizations of the system are investigated in detail.

More results on the Ashkin-Teller model

We analyze the low-temperature phase diagram of the Ashkin-Teller model for real values of the quadratic and quartic coupling constants.

Phase diagrams of thin free films with higher spin values and amorphous surfaces

The critical behavior of ferromagnetic thin free film with higher spin values and two amorphous surfaces is investigated by the use of effective field theory with correlations. The effects of crystal-field terms at the surfaces and in the bulk are discussed. Some interesting results as the possibility of re-entrant behavior are reported.

New transparent conducting oxide based on doped SnO 2 for solar cells

The full-potential linearized augmented plane wave method (FP-LAPW) based on the density functional theory (DFT) and Boltzmanns Transport theory, are employed to investigate theoretically the electronic structure, optical and electrical properties of Sc, Ti and V doped rutile SnO2. The FP-LAPW based on the new potential approximation known as the Tran-Blaha modified Becke-Johnson exchange potential approximation (mBJ). The calculated band structure and density of states (DOS) exhibit a band gap of pure SnO2 (3.3 eV) closer to the experimental one. As well, our results indicate that the average transmittance in the 400 to 1000 nm wavelength region was 90%. The high transmittance and electrical conductivity indicate that doped SnO2 system is a potential as material for solar energy applications.