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[en] According to first-principles density functional calculations, we have investigated the magnetic properties of Mn-doped GaN with defects, Ga1−x−yVGxMny N1−z−tVNzOt with Mn substituted at Ga sites, nitrogen vacancies VN, gallium vacancies VG and oxygen substituted at nitrogen sites. The magnetic interaction in Mn-doped GaN favours the ferromagnetic coupling via the double exchange mechanism. The ground state is found to be well described by a model based on a Mn3+−d5 in a high spin state coupled via a double exchange to a partially delocalized hole accommodated in the 2p states of neighbouring nitrogen ions. The effect of defects on ferromagnetic coupling is investigated. It is found that in the presence of donor defects, such as oxygen substituted at nitrogen sites, nitrogen vacancy antiferromagnetic interactions appear, while in the case of Ga vacancies, the interactions remain ferromagnetic; in the case of acceptor defects like Mg and Zn codoping, ferromagnetism is stabilized. The formation energies of these defects are computed. Furthermore, the half-metallic behaviours appear in some studied compounds. (condensed matter: structural, mechanical, and thermal properties)
[en] The first-principles density functional calculation is used to investigate the electronic structures and magnetic properties of Mn-doped and N-co-doped ZnO nanofilms. The band structure calculation shows that the band gaps of ZnO films with 2, 4, and 6 layers are larger than the band gap of the bulk with wurtzite structure and decrease with the increase of film thickness. However, the four-layer ZnO nanofilms exhibit ferromagnetic phases for Mn concentrations less than 24% and 12% for Mn-doping performed in the whole layers and two layers of the film respectively, while they exhibit spin glass phases for higher Mn concentrations. It is also found, on the one hand, that the spin glass phase turns into the ferromagnetic one, with the substitution of nitrogen atoms for oxygen atoms, for nitrogen concentrations higher than 16% and 5% for Mn-doping performed in the whole layers and two layers of the film respectively. On the other hand, the spin-glass state is more stable for ZnO bulk containing 5% of Mn impurities, while the ferromagnetic phase is stable by introducing the p-type carriers into the bulk system. Moreover, it is shown that using the effective field theory for ferromagnetic system, the Curie temperature is close to the room temperature for the undamped Ruderman—Kittel—Kasuya—Yoshida (RKKY) interaction
[en] In this paper, we used the ab-initio calculations, based on the Korringa-Kohn-Rostoker (KKR) method combined with the coherent potential approximation (CPA), to simulate the magnetic properties of ZnO, doped and co-doped with manganese and carbon, respectively. For this purpose, we have used two different approximations: the Local Density Approximation (LDA) and the Local Density Approximation-Self-Interaction Correction (LDA-SIC). Numerical results are presented for the compound Zn1 − 0.06Mn0.06O1−xCx when doping and co-doping is performed with Mn and C as doping elements. Total and partial DOSs are given for different concentrations using the two approximations, LDA and LDA-SIC. It is found that for 6% with doping by Mn the system becomes magnetic. The co-doping with carbon changes the behavior of the system : it becomes also magnetic for 4, 6 and 10% concentrations within both, LDA and LDA-SIC approximations. Furthermore, we have discussed the type of mechanism of exchange interaction and found that the double exchange is responsible for the appearing magnetism in the system, within the LDA and p-d interaction for LDA-SIC approximation. For 10% of carbon, we have found that the critical temperature approaches 280 K in the LDA approximation solely; and is about 305 K in the LDA-SIC approximation.
[en] In this work, using the ab-initio calculations, we have investigated the phantom magnetism when the diamagnetic solids, carbon and nitrogen with d doped CdTe. We have applied in these calculations the combination between the Korringa-Kohn-Rostoker and coherent potential approximation method within the local density approximation and generalized gradient approximation (GGA). In this study, the doped compound presents a metallic behavior for both the approximations characterized by a small moment of about 0.299/0.326 and 0.249/0.266 μ for 24% of C and N, respectively. The polarization has shown a low and decreasing value from 43.73/59.56 to 0.29/2.26% for 9% and 24% of C impurity concentration, respectively. Unlike for the case of N, this parameter varies from 76.7/72.86 to 85.29/83.63% for 9% and 24% concentration, respectively. In addition, we have determined the mechanism of ferromagnetic coupling for the C- and N-doped CdTe. Furthermore, the stability of the compound is investigated by comparing the energy difference between the spin glass and ferromagnetic states. It is found that below the percolation threshold, contrary to the case of doping by N except for 20% using GGA, the C impurities lead to the most ferromagnetic stable phase. While the system changes its stability above this threshold when doped by the C impurities. Finally, we have estimated and discussed the Curie temperature using the mean field approximation.
[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] On the basis of ab-initio calculations and Monte Carlo simulations the magnetic and electronic properties of Gallium nitride (GaN) doped with the transition metal Manganese (Mn) were studied. The ab initio calculations were done using the AKAI–KKR–CPA method within the Local Density Approximation (LDA) approximation. We doped our Diluted Magnetic Semiconductor (DMS), with different concentrations of magnetic impurities Mn and plotted the density of state (DOS) for each one. Showing a half-metallic behavior and ferromagnetic state especially for Ga_0_._9_5Mn_0_._0_5N making this DMS a strong candidate for spintronic applications. Moreover, the magnetization and susceptibility of our system as a function of the temperature has been calculated and give for various system size L to study the size effect. In addition, the transition temperature was deduced from the peak of the susceptibility. The Ab initio results are in good agreement with literature especially for (x=0.05) of Mn which gives the most interesting results. - Highlights: • The AKAI–KKR–CPA method has been applied to study the doped compound GaN:Mn. • The local density approximation (LDA) has been applied. • The ab-initio calculations have been performed. • The density of states (DOS) have been plotted for differents doping concentrations, using Monte Carlo simulations
[en] The half-metallic ferromagnetic behavior of rare-earth nitride Gd0.95 TM0.05N (TM = Ti, V, Cr, Mn and Co), based on diluted magnetic semiconductors (DMSs), is investigated using the Korringa–Kohn–Rostoker (KKR) method combined with the coherent potential approximation (CPA) within a framework of density functional theory (DFT). The energy difference between the ferromagnetic and disorder local moment states has been evaluated. The exchange interactions obtained from first-principles calculations resulted in ferromagnetic states with Curie temperatures within the ambient conditions. Moreover, the optical absorption spectra obtained by ab initio calculations confirm the ferromagnetic stability based on the charge state of magnetic impurities.
[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] SnO2:TM (V, Cr, Mn and Fe) based dilute magnetic semiconductors are investigated within self-interaction-corrected local density approximation (LSDA-SIC) from first-principles calculation. LSDA-SIC results are compared with the calculated ones within standard LSDA, the stable magnetic state of the system is evaluated by comparing the total energies of ferromagnetic state and spin-glass state. The Ferromagnetic and half metallic behaviors was observed and conformed with the local-moment-disordered state energy for LSDA and LSDA-SIC approximation in [Sn 0.95 TM 0.05 (V, Cr, Mn and Fe)]O2. 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.
[en] Using a composition of first-principle density functional theory (DFT) calculations and Monte Carlo simulation with the calculation within the self-interaction-correction local-density approximation, the electronic, magnetic, and optical properties of doped and co-doped GaN (Ga1−xCrxN, Ga1−xNixN) and GaN (Ga1−2xCrxNixN) (x = 0.03 and 0.06), respectively, have been investigated. Our results have proven that the half-metallic ferromagnetic state still persists of co-doped GaN. In comparing the total energies, ab initio calculations certify the magnetic-state stability of the ferromagnetic phase compared with the spin-glass state. The exchange interactions obtained from the ab initio calculations were used as input parameters in a classical Ising model by Monte Carlo simulation to confirm the half-metallic ferromagnetic states with high Neel temperature.