Results 1 - 10 of 11
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[en] The magnetic order-disorder layering transitions of a spin-1 Ising model are investigated, under the effect of a variable surface crystal field Δs, using the mean-field theory. Each layer k, of the film formed with N layers, disorders at a finite surface crystal field distributed according to the law Δk=Δs/kα, k=1,2,...,N and α being a positive constant. We have established the temperature-crystal field phase diagrams and found a constant tricritical point and a reentrant phenomenon for the first k0 layers. This reentrant phenomenon is absent for the remaining N-k0 layers, but the cricritical points subsist and depend not only on the film thickness but also on the exponent α. On the other hand, the thermal behaviour of the surface magnetisation for a fixed value of the surface crystal field Δs and selected values of the parameter α are established
[en] The effects of alternating transverse fields Ωa and Ωb on the critical behavior of an alternating spin-1 Ising superlattice are studied within an effective field theory with a probability distribution technique that accounts for the single-site spin correlation. Critical temperatures are calculated as a function of the thickness of the superlattice and the strength of the transverse field. Depending on the values of the transverse fields Ωa and Ωb, the critical temperature can increase or decrease with increasing the thickness of the film, such result is not obtained in the uniform transverse field case (Ωa = Ωb). Furthermore, for each thickness L of the film, a long range ordered phase persist at low temperature for selected values of the transverse field Ωa and arbitrary values of Ωb. The effects of interlayer and intralayer exchange interactions are also examined
[en] The perovskite type oxide SrHfO had a huge scientist interest for the past few years thanks to its properties, which allowed it to be applied in different area, in our case we focused on the photovoltaic field application and it is known that this technology has been based on the use of semiconductors with a specific gap value since its birth, which indicates that the gap value is an important element who influences on the efficiency of panels. The aim of our work is based on reducing the gap value by applying different percentage of doping SrHfOS (x = 0%, 8% and 16%) and the determination of electronic and optical properties of all percentage of S using density functional theory (DFT). As a result we reduced the gap value from 5.60 eV corresponding to 0% of S to 2.09 eV corresponding to 16% of S and the band gap is changed from an indirect band gap equivalent to 0% of S to a direct band gap for 8% and 16% of S.
[en] A Monte Carlo (MC) simulation has been used to study the magnetic properties of an antiferromagnetic surface which is coupled ferromagnetically to a ferromagnetic layer. The influence of different exchange interactions on the phase diagram of the surface has been investigated. We have found that in the ordered phase, depending on the values of the exchange interactions, the antiferromagnetic surface can change to ferromagnetic or ferrimagnetic phases. Furthermore, in the case of a bilayer surface, the layering antiferromagnetic-ferromagnetic or ferrimagnetic transitions occur
[en] MgH_2: TM (TM: V, Cr, Mn, Fe, Co, Ni) based dilute magnetic semiconductors (DMS) are investigated using first principle calculations. Our results show that the ferromagnetic state is stable when TM introduces magnetic moments as well as intrinsic carriers in TM: Co, V, Cr, Ti; Mg_0_._9_5TM_0_._0_5H_2. Some of the DMS Ferro magnets under study exhibit a half-metallic behavior, which make them suitable for spintronic applications. The double exchange is shown to be the underlying mechanism responsible for the magnetism of such materials. The exchange interactions obtained from first principle calculations and used in a classical Ising model by a Monte Carlo approach resulted in ferromagnetic states with Curie temperatures within the ambient conditions. - Highlights: • The half-metallic aspect was proven to take place for Ti, Cr, Co and Ni. • The TM impurities are shown to introduce the magnetic moment that makes MgH_2 good candidates for spintronic applications.
[en] We study the substrate inhomogeneity effect on the wetting of a spin-1/2 Ising ferromagnetic film in an external magnetic field H, using Monte Carlo simulations. It is found that the inhomogeneity leads to the formation of clusters of positive and negative spins in each layer. However, depending on the values of H, for a fixed surface magnetic field H s, each layer exhibits three different phases; totally wet, non wet and partially wet. In the latter case, we show the existence of three distinct configurations namely: A configuration in which the layer is partially wet with a total disconnection between clusters PWTD; a configuration in which the layer is partially wet with a partial disconnection between clusters PWPD; the configuration in which the layer is partially wet and the clusters are totally connected PWTC. Furthermore, we show that an increase of H s values breaks the bonds connecting some clusters of the phase PWTC which leads to an expansion of the PWPD region. On the other hand, the frequency distribution and the average size of clusters are investigated in the PWTD region for fixed values of temperature T, H s and H. Moreover, we show the existence of 3D-islands resulting from the formation of islands in each layer
[en] Based upon the first principal spin density functional calculation, the electronic, magnetic and optical properties of ZnTMSe and ZnMnTMSe where TM=Fe, Cr, Co are studied using the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) method within the local density (LDA)and the self-interaction-corrected(SIC) approximation. The purpose of this study is to determine the effect of different type of dopant and concentration on ferromagnetic and half metallic behavior of ZnSe. Therefore the magnetic disorder local moment (DLM) and the ferromagnetic state are investigated for different concentrations of Mn, Fe, Cr and Co; also the advantages of co-doped ZnSe with TM elements, behavior at room temperature are discussed. The electronic structure and optical properties are studied employing the local density (LDA) and the self-interaction-corrected (SIC) approximation. Moreover, the X-ray spectra modeling are in good agreement with the electronic and magnetic properties results. - Highlights: • The magnetic properties of ZnSe codoped with MnY(Y: Fe, Cr, Co) has been investigated. • The half-metallic appears in ZnSe codoped with impurities at low concentration. • The advantages of codoped ZnSe with impurities at room temperature are discussed.
[en] Based on first-principles spin-density functional calculations, using the Korringa–Kohn–Rostoker method combined with the coherent potential approximation, we investigated the half-metallic ferromagnetic behavior of (Ga, Fe)N co-doped with carbon within the self-interaction-corrected local density approximation. Mechanism of hybridization and interaction between magnetic ions in p-type (Ga, Fe)N is investigated. Stability energy of ferromagnetic and disorder local moment states was calculated for different carbon concentration. The local density and the self-interaction-corrected approximations have been used to explain the strong ferromagnetic interaction observed and the mechanism that stabilizes this state. The transition temperature to the ferromagnetic state has been calculated within the effective field theory, with a Honmura–Kaneyoshi differential operator technique. - Highlights: ► The paper focus on the study the magnetic properties and electronic structure of p-type (Ga, Fe)N within LDA and SIC approximation. ► These methods allow us to explain the strong ferromagnetic interaction observed and the mechanism for its stability and the mechanism of hybridization and interaction between magnetic ions in p-type (Ga, Fe). ► The results obtained are interesting and can be serve as a reference in the field of dilute magnetic semi conductor.
[en] Using the first principles calculations the magnetic and electronic properties of (Cr, V) co-doped ZnO have been studied. The ground state of Cr doped ZnO exhibits ferromagnetic order. The ferromagnetic state and the half metallicity, with 100% spin-polarization, can be stabilized when (Zn, Cr) O is co-doped with V. The magnetic moments of (Zn1−x−yVxCry)O mainly arise from the V atom with a little contribution from the Zn atoms, and both the Cr and V magnetic moments increase with the increase of V concentration. The obtained results are in good agreement with known experimental results on Cr and V-doping of ZnO which show a ferromagnetic behavior at room temperature. - Highlights: • Ferromagnetic state and the half metallicity, can be stabilized when (Zn, Cr) O is co-doped with V. • The magnetic moments of (Zn1−x−yVxCry)O mainly arise from the V atom. • Cr and V-doped ZnO exhibits ferromagnetic behavior at room temperature
[en] Highlights: • SnFe2O4 a new half-metal spinel oxides for spintronic application. • The most stable normal spinel structures are identified for SnFe2O4. • Spin-polarized calculations give a half-metallic character for SnFe2O4. - Abstract: In this work, a study of the electronic and magnetic properties of SnFe2O4 spinel ferrite for different case of octahedral and tetrahedral distribution was carried out by using the Full Potential Linearized Plane Wave (FP-LAPW) method in density functional theory (DFT) implemented in the WIEN2K package, with the generalized gradient (GGA) and Tran-Blaha modified Becke-Johnson approximations for the exchange and correlation functional. Our spin-polarized calculations based on mBJ correction show a half metallic behavior for SnFe2O4 which confirm the usefulness of SnFe2O4 in spintronic application. From the magnetic properties calculations, it is found that the magnetic moment per formula unit is 8.0327 µβ, 0.000015 µβ and 3.99µβ in SnFe2O4 100% normal, 100% inverse and 50% inverse, respectively.