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A. Fakhim Lamrani M. Belaiche A. Benyoussef A. El Kenz 《Journal of magnetism and magnetic materials》2010,322(4):454-458
The electronic structure and ferromagnetic properties of rutile TiO2 doped with double-impurities Ti1−2xCrxMnxO2 has been investigated using first-principles calculations within the density-functional theory (DFT) and the local density approximation (LDA), functional for treating the effects of exchange and correlation. They were performed using the scalar-relativistic implementation of the augmented spherical wave (ASW). The advantages of doping TiO2 with double impurities instead of single impurities are the increase of the total moment of the system and the exhibition of the half-metallic ferromagnetic nature in Cr- and Mn-doped TiO2 rutile. These behaviors are due to the hybridization of Cr 3d states and nearest-neighboring O 2p states. The spin-spin interaction between magnetic impurities examined by the total energy between parallel and antiparallel aligned states indicated that the Cr and Mn impurities are energetically favorable to be parallel coupled, which mean that the ferromagnetic state is more stable than the ferrimagnetic one. We proposed a bond magnetic polarons (BMP) model, based on localized carriers, to explain the mechanism of ferromagnetism in these systems. 相似文献
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Dilute magnetic oxides are without doubt among the most interesting classes of magnetic materials. However, the nature of their electronic structure and magnetic exchange is far from understood. Here, we apply the ab initio augmented spherical wave (ASW) method, with corrected generalised gradient approximation to study the electronic structure and magnetic properties of doped TiO2 rutile with double impurities. The study reveals a half-metallic ferromagnetic behaviour for Ti1?2x Cr x Mo x O2, and the local magnetic moments of the impurities and their oxidation states agree with the charge transfer between Cr and Mo, which would lead to the ferromagnetic state through the double-exchange mechanism in transition metal oxides. 相似文献
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M. Alaoui Lamrani Z. Sofiani B. Sahraoui A. El Hichou J.C. Bernède 《Optics Communications》2007,277(1):196-201
We have deposited zinc oxide (ZnO) and erbium doped zinc oxide (ZnO:Er) thin films on heated glass substrates using spray pyrolysis technique. The effect of erbium dopant on structural, morphological, luminescent and nonlinear optical properties was studied. The deposited films have been analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), ex situ compositional analysis (ESCA), profilometry, cathodoluminescence (CL) and third harmonic generation (THG) measurements. All films were polycrystalline, having a preferential growth orientation along the ZnO (0 0 2) plane, with a corresponding average crystallite size of less than 41 nm. Addition of erbium can effectively control the film surface morphology and its cathodoluminescent properties. The films containing low erbium concentration show a uniform surface covered with hexagonal shaped grains and a strong UV light emission intensity as well as TH response. In contrast, when the erbium doping ratio exceeds 3%, a porous surface with columnar textural growth becomes more pronounced, and a substantial reduction of the cathodoluminescent and TH response. A strong TH signal was obtained for the film with good crystalline quality at the concentration of 2%. Third order nonlinear optical susceptibility (χ〈3〉) values of the studied materials were in the remarkable range of 10−12 esu. 相似文献
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Iron oxide thin films were prepared by spray pyrolysis technique onto glass substrates from iron chloride solution. They were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and (UV-vis) spectroscopy. The films deposited at Ts ≤ 450 °C were amorphous; while those produced at Tsub = 500 °C were polycrystalline α-Fe2O3 with a preferential orientation along the (1 0 4) direction. By observing scanning electron microscopy (SEM), it was seen that iron oxide films were relatively homogeneous uniform and had a good adherence to the glass substrates. The grain size was found (by RX) between 19 and 25 nm. The composition of these films was examined by X-ray photoelectron spectroscopy and electron probe microanalysis (EPMA). These films exhibited also a transmittance value about 80% in the visible and infrared range. The cyclic voltammetry study showed that the films of Fe2O3 deposited on ITO pre-coated glass substrates were capable of charge insertion/extraction when immersed in an electrolyte of propylene carbonate (PC) with 0.5 M LiCLO4. 相似文献
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Z. Sofiani B. Derkowska M. Wojdy?a M. Alaoui Lamrani W. Ba?a B. Sahraoui 《Optics Communications》2006,267(2):433-439
In this paper, zinc oxide (ZnO) and cerium-doped zinc oxide (ZnO:Ce) films were deposited by reactive chemical pulverization spray pyrolysis technique using zinc and cerium chlorides as precursors. The effects of Ce concentration on the structural and optical properties of ZnO thin films were investigated in detail. These films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) measurements. All deposited ZnO layers at the temperature 450 °C are polycrystalline and indicate highly c-axis oriented structure. The dimension of crystallites depends on incorporation of Ce atoms into the ZnO films. The photoluminescence spectra of the films have been studied as a function of the deposition parameters such as doping concentrations and post grows annealing. Photoluminescence spectra were measured at the temperature range from 13 K to 320 K. 相似文献
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A. Fakhim Lamrani M. Belaiche A. Benyoussef A. El Kenz E.H. Saidi 《Journal of magnetism and magnetic materials》2011,323(23):2982-2986
Using the augmented spherical wave method, the electronic structure and magnetic properties of the rutile SnO2 doped with single and double impurities: Sn1−xMnxO2, Sn1−xWxO2, and Sn1−2xMnxWxO2 with x=0.0625, have been studied. The scalar-relativistic implementation with a generalized gradient approximation functional has been used for treating the effects of exchange and correlation. The ground state of Mn-, and W-doped SnO2 systems have a total magnetic moments of 3 and 2 μB, respectively. The half-metallic nature appears in Sn1−2xMnxWxO2, which makes them suitable as spintronic systems with total magnetic moment of 5 μB. The advantages of doping SnO2 with double impurities are investigated in this work. The total moment of the system, the local magnetic moments of the impurities, and their oxidation states are also discussed. Since there are two possible couplings between the impurities, we studied both configurations (ferromagnetic and antiferromagnetic) for double-impurities-doped SnO2. Magnetic properties and interatomic exchange have been computed for various distances between Mn and W. The indirect exchange between double impurities has similarities with the Zener mechanism in transition metal oxides. Based on the interaction between localized moments, via hybridization between impurities orbitals with the host oxygen, a double exchange mechanism is proposed to explain the ferromagnetism of our system. 相似文献
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