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[en] In this study, the electronic structure of V-doped ZnO system is studied by means of density functional theory. Different concentrations of V and rising of Fermi level increase the relative occupation of majority/minority spin of 3d state and also induce strong spin-splitting. The existence of three different states of V spin moment has been confirmed and is found to be concentration dependent. We found that O p-orbitals are responsible for the origin of the magnetic moment. Ruderman–Kittel–Kasuya–Yosida mechanism and the atomic spin polarization of V are the key factors for the appearance of ferromagnetism in V-doped ZnO system. The synthesized nanoparticles exhibit hexagonal wurtzite crystal structure, where both crystallite size and lattice parameters vary with V content. Magnetic measurements at room temperature confirm the ferromagnetic behaviour of V-doped ZnO system.
[en] In this paper, the magnetism of ZnO with wurtzite-type structure, when doped with Fe then co-doped with (Fe,V) was investigated by density functional theory. Furthermore, the difference between the ferromagnetic and the disordered local moment in term of magnetic energy indicated the stabilization of the magnetic phase in diluted magnetic semiconductors. It was revealed that the semi-metallic behaviour in Zn0.95Fe0.05O composition was transferred to a half-metallic behaviour with co-doping with V. Hence, the Fermi level was crossed by the majority-spin valence states, meanwhile, a gap occured in the Fermi level of the minority-spin states. A large replacement splitting was detected between V 3d states of the majority-spins and the minority-spins. The estimated Curie temperature was found to increase with V content. X-ay diffraction Rietveld analysis revealed that the co-doping of ZnO with Fe and V maintains the wurtzite crystal structure and that the crystallite size increased with doping concentration, i.e. 15–52 nm. Hysteresis loops indicated the appearance of room temperature ferromagnetism, where the magnetic properties were found to be very sensitive to the nature of the doping element (Fe and Fe-V) as well as its concentration. Both ab initio calculations and experimental results were found in good agreement. The observed changes in the magnetic parameters were attributed to a combination of various parameters, such as the substitution by the magnetic Fe and the non-magnetic V atoms, formation of small crystals in the nanoscale regime, the increase of crystallite size and grain boundaries. (paper)
[en] 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. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
[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] Structural, optical and room temperature magnetic properties of Mn-doped MgO nanoparticles with Mn fractions (5–50 at.%), were investigated. The as-prepared pure MgO, with grain size of about 15 nm, exhibits two magnetization components, one is diamagnetic and another is superparamagnetic. After removing the diamagnetic contribution, the magnetization curve exhibits superparamagnetic behavior which may be attributed to vacancy defects. As the Mn content increases, the lattice parameter decreases, the ferromagnetism appears and the emission bands were considerably blue shifted. First principle electronic structure calculations reveal the decrease of both the gap and the Curie temperature with increasing Mn concentration. The obtained results suggest that both Mn doping and oxygen vacancies play an important role in the development of room temperature ferromagnetism. - Graphical abstract: The measured room temperature magnetization curve for the Mn doped MgO with 5 at.%, 10 at.% and 20 at.%. - Highlights: • Combination of experimental and calculation methods. • Decrease of both the gap and the Curie temperature with increasing Mn content. • Ferromagnetism in MgO originate from interactions between defects
[en] Graphical abstract: Magnetization, neutron diffraction and KKR-CPA calculations are employed to investigate the magnetic properties of nanostructured doped ZnO. - Abstract: Nanostructured doped-ZnO system with various elements (M = Cr, Mn, Fe, Co, Ni, and In) at 10 at.% doping concentration, was investigated. Neutron diffraction refinements confirm the stability of the würztite crystal structure of the parent compound ZnO, the localization of the doping elements within Zn sites, and some residual impurities. Magnetic measurements show a ferromagnetic behavior at room temperature where the magnetic parameters, saturation magnetization (Ms), remanence (Mr) and coercivity (Hc) vary considerable according to the nature of the doping elements, its valence and its solubility level: Ms has the highest value of 0.223 emu/g for Ni and lowest value of 0.011 emu/g for Cu. The ab-initio calculations using DFT method confirm the ferromagnetism of doped-ZnO in agreement with magnetic measurements. It is found that oxygen plays an important role to explain the magnetic properties observed in diluted magnetic semiconductors (DMS) of the studied doped-ZnO system. The estimated Curie temperature was found to vary considerably according to the nature of the doping element, with the lowest value for In (105 K) and highest value for Co (737 K).