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First principle investigation of structural, electronic and magnetic properties of cubic Cd0.9375TM0.0625S (TM = Ni, Co and Fe)
Abstract
In this study, we investigated the structural, electronic and magnetic properties of Cd0.9375TM0.0625S (TM = Ni, Co and Fe) compounds in zinc blende (B3) ferromagnetic phase using all-electron full-potential linear muffin tin orbital (FP-LMTO) calculations within the frame work of the density functional theory and the generalized gradient approximation. The analysis of electronic structures shows that Cd0.9375Ni0.0625S, Cd0.9375Co0.0625S and Cd0.9375Fe0.0625S compounds are half-metallic ferromagnets with 100% spin polarization at the Fermi level. This half-metallic behavior is confirmed by the total calculated magnetic moment per Ni, Co and Fe substituted transition metal (TM) atom, which is found to be 2 µB, 3 µB and 4 µB for Cd0.9375TM0.0625S (TM = Ni, Co and Fe) compounds, respectively. Furthermore, we found that the TM-3d states are responsible for generating spin-polarization and magnetic moment in these compounds and we establish that the p-d hybridization reduces the local magnetic moment of TM atoms from its free space charge value and produces small local magnetic moments on nonmagnetic Cd and S host sites. Also, we predicted exchange splitting energy Δx(pd) and exchange constants N0α and N0β. The calculated values validate the ferromagnetic nature of these compounds.
... Here, in the present case, the spin-up and spin-down states are reverted due to the quantum confinement effect in which wave functions of electrons are bound in the quantum well [38]. A strong hybridization exists between Fe-3d and S/Se-p states, which manipulate ferromagnetic interaction [39]. In lower energy region, −4 eV to −1 eV, 3d-e .g. states are highly contributed to spin up channel as compared to spin down channel. ...
Magnesium-based spinel chalcogenides are remarkable materials for spintronic and energy harvesting applications. Therefore, the electronic, ferromagnetism, and thermoelectric characteristics of MgFe2(S/Se)4 spinels are addressed comprehensively by modified Becke Johnson potential (TB-mBJ). The stability of cubic phase has been illustrated by formation energy and energy released during optimization. The Curie temperature and spin polarization have been calculated by Heisenberg model and density of states at Fermi level. Ferromagnetism has been studied by exchange energies, double exchange mechanism, exchange constants, and hybridization process. The reduction of magnetic moment of Fe and its shifting on nonmagnetic (Mg, S/Se) sites shows the ferromagnetism is due to the exchange of electrons spin rather than the clustering effect of internal magnetic of Fe atoms in the structure. Moreover, thermoelectric analysis of studied spinels has been illustrated by electrical and thermal conductivities, Seebeck coefficient (S), and power factor.
... Moreover, the effects of other dopants such as Cr, V, Ni, Co, and Fe in ZnX (X = O, Te, Se) were also studied by Sato et al. where the ferromagnetic state was found to be more energetically favorable than its antiferromagnetic counterpart (Sato et al. 2002).To many organizations have begun a series of theoretical and experimental studies on a variety of TM-doped CdS in recent decades, whereas ferromagnetic behavior has been extensively described (Nazir et al. 2009;Saeed et al. 2010;Bourouis et al. 2012;Benstaali et al. 2014;Yahi et al. 2016Yahi et al. , 2017Gous et al. 2017). ...
This paper investigates in detail the structural, magnetic, and optoelectronic properties of Cd0.75TM0.25S (TM = Os and Ir) alloys having a zinc-blende structure of the ferromagnetic phase using the full potential linearized augmented plane-wave (FP-LAPW) method as implemented in the Wien2k package. The exchange–correlation potential was treated with the generalized gradient approximation (GGA). Moreover, the GGA + U + SO approximation (where U denotes the Hubbard Coulomb energy and SO is the spin orbit coopling) are employed to treat the d electrons properly. The analysis of the values of formation energy, formation enthalpy, phonon spectra and the exchange interaction parameters show that the investigated alloys are stable and can be synthesized. The densities of states (DOS) indicate that Cd0.75TM0.25S (TM = Os and Ir) exhibits metallic nature using both GGA and GGA + SO. The half-metallic nature for Cd0.75Os0.25S and the ferromagnetic half-semiconductor nature for Cd0.75Ir0.25S have been predicted by GGA + U. Both considered alloys become ferromagnetic-semiconductors by using GGA + SO + U, where the computed band gaps are 0.52 for Cd0.75Os0.25S and 0.72 for Cd0.75Ir0.25S. The dielectric function's real and imaginary portionsε′ω,ε″ω, absorption coefficient α(ω), and refractive index n(ω) were evaluated using a radiation range up to 30 eV. For CdS, the observed results are on par with previously published experimental and theoretical results. Our findings imply that these materials might be of potential use in future spintronic devices.
... The sustained long-range ferromagnetic behavior is attributed to neighboring atoms' electron polarization surrounding the vanadium. The phenomenon is called the RKKY effect [34]. The negative values of indirect exchange energy indicate that ferromagnetism is induced due to the exchange mechanism. ...
Understanding ferromagnetism and thermoelectric behavior are crucial in spintronics and thermoelectric device applications. Using density functional theory-based WIEN2k code, we have examined the physical properties of vanadium-based MgV 2 S/Se 4 spinels. The calculated negative formation energies and positive phonon frequency indicate the stability of the studied system. The lowest energy ground state has been predicted to be a ferromagnetic phase. The calculated electronic band structure and density of states show that these materials are half-metallic ferromagnetic. The existence of the ferromagnetic phase is described using the pd hybridization, double exchange interaction model by computing the exchange energy and constants. In addition, the quantum coupling of electrons is caused by the shift of the magnetic moment from the V site to non-magnetic sites (S/Se, Mg). Finally, electronic transport parameters like the Seebeck coefficient, electric and thermal conductivity, and power factor are also determined.
... The crystal field energy which is induced in structures due to tetrahedral environment of S/Se ions split the 3d-states of Mn into doublet and triplet states. The doublet states are nonlinear e g (dz 2 , dx 2 -y 2 ) while triplet states are linear t 2g (d xy , d yz , d zx ) [30]. Under the frame work of tetrahedral strain force, the linear states (t 2g ) move at higher energy while nonlinear states (e g ) moves to lower energy. ...
The structural, mechanical, electro-magnetic and transport attributes of ZnMn2X4 (X= S and Se) spinels are explored by density functional theory (DFT). The stability in structures are affirmed by negative formation energy. Moreover, structural optimizations have suggested studied compounds are stable in ferromagnetic phase. This phenomenon is also endorsed in electronic properties by band structures and density of states. In magnetic properties, ferromagnetic nature is discussed in detail by pd hybridization process, double exchange model, exchange energies and exchange constants. It is found that negative exchange constant N0β lower the ground energy of system which is in conformity to the double exchange mechanism. Furthermore, the magnetic moment shifting observed at Mn site to nonmagnetic sites (Zn, S/Se) is due to quantum coupling of electrons. Finally transport properties are evaluated by finding electrical conductivity, thermal conductivity, Seebeck coefficient and power factor. All these parameters are in support of the compounds, which suggest novel spintronic applications.
Based on the full-potential linearized augmented plane wave (FP-LAPW) method, we have investigated the electronic, structural, magnetic and optical properties of Cd0.9375TM0.0625S (TM = Mn, Fe, Co and Ni) compounds in the zinc-blende (ZB) ferromagnetic phase. The magnetic and electronic properties are treated using the PBE-GGA and TB-mBJ approximations. CdS is well known as a non-magnetic semiconductor. When CdS is doped with a transition metal (TM), Cd0.9375TM0.0625S (TM = Mn, Fe, Co) changes to half-semiconductors (HSC) and Cd0.9375Ni0.0625S to a half-metal (HM). It is found that the 3d-t2g states of the transition metal are responsible for generating spin polarization and magnetic moment in these compounds. All the considered compounds are ferromagnetic and the calculated total magnetic moment increases from 2 to 5 µB moving from Ni to Mn. The optical properties exhibited new peaks in the visible and ultraviolet regions due to the effect of free-carrier absorption related to the magnetic impurities. Our results show very good agreement to previous theoretical and experimental data. The results presented herein imply that TM-doped CdS has potential for applications in spintronic and optoelectronic device sectors in a wide energy range of the light spectrum from visible to ultraviolet.
The doping of boron phosphide (BP) with manganese as magnetic impurity at different concentrations provides metallic ferromagnetic materials B[Formula: see text]Mn x P at ([Formula: see text], 0.125, 0.0625). Their structural and electronic properties are calculated by the first-principle spin-density functional theory (DFT) within the framework of the Wu–Cohen generalized gradient approximation (WC-GGA). The DMSs BP originated from doping manganese contributed in SP3 hybridization of tetrahedral crystal field caused by the surrounding of four phosphorus anions. These compounds are not half-metallic but exhibit a poorly metallic ferromagnetic nature, the cause is due to the highly covalent chemical bond of BP. The B[Formula: see text]Mn x P are metallic ferromagnetic materials and are not to be intended for spintronic industry.
To probe the applications in spintronics and sustainable energy devices of ZnMn2X4 (X=S, Se, Te) spinels, their structural, elastic, electronic and thermoelectric properties have been studied in the present work. Structural properties reveal stability of ferromagnetic (FM) phase in these spinels which is further confirmed by computing the heat of formation for these compounds. The mechanical properties of the ZnMn2X4 spinels have been investigated by computing their elastic constants, which show that all these spinels exhibit a brittle character. Moreover, electronic band structure and density of states reveal a half-metallic FM structure in all these spinels. Analysis of the band structure of these materials reveals a semiconducting nature in the spin down channel. Exchange constants (N0α and N0β) have been computed to directly probe the state splitting and our results large splitting of Mn 3d-states by N0β owing to its larger negative value as compared to N0α. The strong p-d hybridization is found to make exchange field dominant to crystal field which consequently induces ferromagnetism. In addition, the p-d hybridization reduces the magnetic moment of Mn ions by inducing traces of magnetic moments at non-magnetic sites. The observation of thermoelectric behavior within temperature range 200K–800K reveals positive Seeback coefficient indicating holes as majority charge carriers. Although the power factor is found to increase on going from ZnMn2S4 to ZnMn2Te4, our results clearly show improvement of power factor with increasing temperature.
Our aim in this paper is to study the influence of doping with transition metals (TM) on the physical properties of CdS. Thus, the structure stability, half-metallic ferromagnetic, and electronic properties of Cr-, V-, Mn-, Cu-, and Sc-doped CdS, at x = 0.0625 concentration have been investigated using first principle calculations based on the density functional theory (DFT). The all-electron full-potential linear Muffin-Tin orbital (FP-LMTO) method and the generalized gradient approximation (GGA) have been employed. The electronic properties indicate that the Cd0.9375Cu0.0625S and Cd0.9375Sc0.0625S compounds are magnetic degenerate semiconductors and the Cd0.9375Mn0.0625S compound is p-type magnetic semiconductor, while the Cd0.9375Cr0.0625S and Cd0.9375V0.0625S compounds are half-metallic ferromagnets. We have also found that the TM-3d states are responsible for the spin-polarization and the induction of magnetic moments in these compounds. Additionally, to explain the origin of half-metallic ferromagnetism, we have calculated the exchange splitting energy Δx(pd) and the exchange constants N0α and N0β. The calculated values suggest that the Cd0.9375Cr0.0625S and Cd0.9375VV0.0625S compounds may be useful for the development of spintronic devices.
In this paper, we have investigated the structural, electronic, and magnetic properties of magnesium selenium (MgSe) doped with transition metal manganese (Mn) impurity in the cubic diluted magnetic semiconductor (DMS) zinc blende structure. The compounds which we are interested are as Mg1−xMnxSe where x change between 0 and 1 by step 0.25. All properties are studied, using first-principles calculation of density functional theory under the framework of the full-potential linearized augmented plane waver (FP-LAPW). In our study, we employed the Wu-Cohen generalized approximation (WC-GGA) to optimize the crystal structure, whereas Tran-Blaha modified Becke-Johnson potential (TB-mBJ) as a new functional was applied to compute the electronic and magnetic properties in order to get some better degree of precision. The electronic band structures and density of state plots reveal ferromagnetic semiconducting behavior in these compounds, and the exchange constants N0α and N0β are calculated to validate the effects resulting from exchange splitting process. Moreover, for each concentration x, the value of total magnetic moment has been estimated to equal to 5 μB. The important magnetic moments values obtained in these compounds indicate the potential for their use in spintronic devices.
The structural, electronic, and half-metallic ferromagnetic properties of ordered zinc blende Al 1−xMn xP diluted magnetic semiconductors with concentrations (x = 0.0625, 0.125, and 0.25) are studied using first-principle calculations of density functional theory in order to seek out the possibility to use these materials for the spin injection in the field of spintronic applications. The electronic structures of Al 1−xMn xP at all concentrations exhibit a half-metallic ferromagnetic behavior with 100 % magnetic spin polarization and half-metallic gap. While, the analysis of partial densities of states reveals that strong hybridization between 3p (P) and 3d (Mn) partially filled states dominates the gap, which stabilizes the ferromagnetic state configuration associated with double-exchange mechanism. Also, the magnetic proprieties prove an integer total magnetization of 4 uB that confirms the half-metallic ferromagnetic feature of Al 1−xMn xP compounds.
First-principle calculations within the framework of density functional theory are employed to study the electronic and half-metallic ferromagnetic properties of Be1−x
Cr
x
S at concentrations x = 0.0625, 0.125, and 0.25 in zinc-blende phase. The calculations of electronic and magnetic properties reveal that Be1−x
Cr
x
S is a half-metallic (HM) ferromagnet with 100 % spin polarization and HM gap. On the other hand, for the majority-spin states, the strong hybridization between 3 p (S) and the 3 d- t
2g
(Cr) partially filled states dominates the gap and this stabilizes the ferromagnetic ground state associated with double-exchange mechanism, while the total magnetization is an integer Bohr magneton of 4 u
B that confirms the half-metallic behavior of Be1−x
Cr
x
S compounds. Therefore, the chrome-doped beryllium sulfide (BeS) seems to be a potential candidate for spin injection in the field of spintronic applications.
First-principle calculations within the framework of density functional theory are employed to study the structural, electronic, and half-metallic ferromagnetic properties of In1−x (TM)x
P (TM = Cr, Mn) at concentrations (x = 0.0625, 0.125, 0.25)of transition metal in zinc blende phase. The investigations of electronic and magnetic properties indicate that In1−xTMx
P (TM = Cr, Mn) at x = 0.0625, 0.125, and 0.25 are half-metallic ferromagnets with 100 % magnetic spin polarization. On the one hand, the total magnetization is an integer Bohr magneton of 3 μ
B and 4 μ
B for In1−xCrx
P and In1−xMnx
P, respectively, which confirms the half-metallic feature of In1−xTMx
P compounds. On the other hand, the densities of states of majority-spin states show that the large hybridization between 3p (P) and 3d (TM) partially filled states dominates the gap, which stabilizes the ferromagnetic state configuration associated with double-exchange mechanism. The band structures depict that half-metallic gap at x = 0.0625 is 0.404 eV for In1−xCrx
P which is higher than 0.125 eV for In1−xMnx
P. Therefore, the largest half-metallic gap in In1−xCrx
P at low concentration x = 0.0625 reveals that Cr-doped InP seem to be a more potential candidate than that Mn-doped InP for spin injection applications in the field of spintronic devices.
This work reports on structural and magnetic investigations of the Heusler compound Co2FeSi. X-ray diffraction and Mo beta bauer spectrometry indicate an ordered L2(1) structure. Magnetic measurements by means of x-ray magnetic circular dichroism and magnetometry revealed that this compound is, currently, the material with the highest magnetic moment (6 mu(B)) and Curie temperature (1100 K) in the classes of Heusler compounds as well as half-metallic ferromagnets. (c) 2006 American Institute of Physics.
We report the parameter-free, density-functional theory calculations of the electronic structure, interatomic exchange interaction and magnetic critical temperature of Zn0.75Cr0.25Te. This system has recently gained exceptional importance as the first diluted magnetic semiconductor (DMS), where the intrinsic ferromagnetism with Curie temperature higher than room temperature is confirmed by magnetic circular dichroism measurements. We obtain a value for the Curie temperature that is in good agreement with experiment. The role of the holes in the valence band in mediating the ferromagnetic exchange interactions is demonstrated. The application of the same calculational scheme to Zn0.75Mn0.25Te shows that, in good correlation with experimental data, this system does not possess charge carriers and is characterized by strong antiferromagnetic exchange interactions. Comparing (ZnCr)Te with III-V DMS, we note the role of a large semiconducting gap for preserving high spin polarization of the states at the Fermi level at finite temperatures.
The properties of diluted Ga1-xMnxAs are calculated for a wide range of Mn concentrations within the local-spin-density approximation of density-functional theory. Mülliken population analyses and orbital-resolved densities of states show that the configuration of Mn in GaAs is compatible with either 3d5 or 3d6; however, the occupation is not integer due to the large p-d hybridization between the Mn d states and the valence band of GaAs. The spin splitting of the conduction band of GaAs has a mean-field-like linear variation with the Mn concentration, and indicates ferromagnetic coupling with the Mn ions. In contrast, the valence band is antiferromagnetically coupled with the Mn impurities, and the spin splitting is not linearly dependent on the Mn concentration. This suggests that the mean-field approximation breaks down in the case of Mn-doped GaAs, and corrections due to multiple scattering must be considered. We calculate these corrections within a simple free-electron model, and find good agreement with our ab initio results if a large exchange constant (Nbeta=-4.5 eV) is assumed.
The crystallographic and magnetic structures of the Ni2XGa (X = Mn, Fe, Co), are systematically investigated by means of the first-principles calculations within the framework of density functional theory using the VIENNA AB INITIO SOFTWARE PACKAGE. The formation energies of several kinds of defects (atomic exchange, antisite, vacancy) are estimated. The Ga atoms stabilize the cubic structure, and the effect of X atoms on the structural stability is opposite. For most cases of the site occupation, the excess atoms of the rich component directly occupy the site(s) of the deficient one(s), except for Ga-rich Ni-deficient type. The magnitude of the variation in Ni moments is much larger than that of Mn in defective Ni2XGa. The value of Ni magnetic moment sensitively depends on the distance between Ni and X. Excess Mn could be ferromagnetic or antiferromagnetic, depending on the distance between the neighboring Mn atoms.
The crystallographic, magnetic and electronic structures of the ferromagnetic shape memory alloys Ni2XGa (X = Mn, Fe, and Co), are systematically investigated by means of the first–principles calculations within the framework of density functional theory using the VIENNA AB INITIO SOFTWARE PACKAGE. The lattice parameters of both austenitic and martensitic phases in Ni2MnGa have been calculated. The formation energies of the cubic phase of Ni2XGa are estimated, and show a destabilization tendency if Mn atom is substituted by Fe or Co. From Ni2MnGa to Ni2CoGa, the down spin total density of states (DOS) at Fermi level is gradually increasing, whereas that of the up spin part remains almost unchanged. This is the main origin of the difference of the magnetic moment in these alloys. The partial DOS is dominated by the Ni and Mn 3d states in the bonding region below EF. There are two bond types existing in Ni2XGa: one is between neighboring Ni atoms in Ni2MnGa; the other is between Ni and X atoms in Ni2FeGa and Ni2CoGa alloys.
a b s t r a c t We report the synthesis of Co-doped CdS nanoclusters (Cd 1−x Co x S) for different doping concentra-tions (x = 0.10, 0.20 and 0.30) and characterization of their structural, optical, and magnetic properties. The structural properties studied by X-ray diffraction revealed hexagonal-greenockite structure and a decrease of the lattice parameters (a and c) with doping, showing incorporation of Co in the lattice. The morphology of the nanoclusters was studied by scanning electron microscopy. The optical absorption studies, using diffused reflectance spectroscopy, revealed that Co doping modifies the absorption band edge. Ferromagnetic phase was observed in the magnetization measurements at room-temperature due to high carrier concentration. X-ray absorption near edge fine structure measurements at the sulfur (S) K-edge of the Co-doped samples revealed that the valence remains divalent and that there are some changes with Co doping in the spectral intensity.
This review summarizes recent first-principles investigations of the electronic structure and magnetism of dilute magnetic semiconductors (DMSs), which are interesting for applications in spintronics. Details of the electronic structure of transition-metal-doped III-V and II-VI semiconductors are described, especially how the electronic structure couples to the magnetic properties of an impurity. In addition, the underlying mechanism of the ferromagnetism in DMSs is investigated from the electronic structure point of view in order to establish a unified picture that explains the chemical trend of the magnetism in DMSs. Recent efforts to fabricate high-${T}_{C}$ DMSs require accurate materials design and reliable ${T}_{C}$ predictions for the DMSs. In this connection, a hybrid method (ab initio calculations of effective exchange interactions coupled to Monte Carlo simulations for the thermal properties) is discussed as a practical method for calculating the Curie temperature of DMSs. The calculated ordering temperatures for various DMS systems are discussed, and the usefulness of the method is demonstrated. Moreover, in order to include all the complexity in the fabrication process of DMSs into advanced materials design, spinodal decomposition in DMSs is simulated and we try to assess the effect of inhomogeneity in them. Finally, recent works on first-principles theory of transport properties of DMSs are reviewed. The discussion is mainly based on electronic structure theory within the local-density approximation to density-functional theory.
Spontaneous severe multivessel coronary artery vasospasm is a rare but important cause of morbidity. One-third of patients have normal coronary vasculature, and these pose a significant therapeutic dilemma as lack of clinical suspicion might potentially lead to unnecessary revascularization therapies. A patient with resting chest pain and ischaemic electrocardiography demonstrated severe coronary obstruction at catheter angiography. Preangioplasty further information highlighted spasm as the likely cause and the angiographic abnormalities resolved post intracoronary nitrate. This paper emphasises thorough history-taking and judicious use of nitrates during diagnostic coronary angiography in such patients. This may negate the need for more complex cardiac interventions.
Results of density-functional calculations for isolated transition metal (TM = V, Cr, Mn, Fe, Co, Ni on cation sites) doped GaN demonstrate a novel magnetic metastability in dilute magnetic semiconductors. In addition to the expected high spin ground states (4muB/Mn and 5muB/Fe), there are also metastable low spin states (0muB/Mn and 1muB/Fe)--a phenomenon that can be explained in simple terms on the basis of the ligand field theory. The transition between the high spin and low spin states corresponds to an intraionic transfer of two electrons between the t2 and e orbitals, accompanied by a spin-flip process. The results suggest that TM-doped wideband semiconductors (such as GaN and AlN) may present a new type of light-induced spin-crossover material.
The objective of this work is to predict the structural, electronic, magnetic and elastic properties of Mg1−xTMxS (TM=Mn, Fe, Co and Ni) compound in the zinc blende Ferromagnetic phase using first principal approach. The structural and elastic properties are performed using the generalized gradient approximation proposed by Wu and Cohen(WC-GGA). However, the electronic and magnetic properties have been performed using modified Becke-Johnson potential combined with the LDA correlation (mBJLDA). The results show that all compounds Mg1−xMnxS, Mg1−xFexS and Mg1−xNixS exhibit a half-metallic ferromagnetic character with 100% spin-polarization at the Fermi level, except Mg1−xCoxS is a metal. For each compounds study here, the total magnetic momentum is an integer equal to magnetic moments of TM atom in their free space charge value. Due to the p–d hybridization, there is a small local magnetic moment on the Mg and S sites; whereas, the local magnetic moments of TM atom reduce from their free space charge value. In addition, we investigate the mechanical behavior of MgS and Mg1−xTMxS; all compounds studied here are mechanically stable and exhibit a strong anisotropic behavior.
The structural, electronic and ferromagnetic properties of Cd1-xTMxS (TM=Co and V) compounds at x=0.25, 0.50 and 0.75 in zinc blende (B3) phase, have been investigated using all-electron full-potential linear muffin tin orbital (FP-LMTO) calculations within the frame work of the density functional theory and the generalized gradient approximation. The electronic properties exhibit half-metallic behavior at x=0.25, 0.50, and 0.75 for Cd1-xVxS and x=0.25 and 0.50 for Cd1-xCoxS, while Cd1-xCoxS with x=0.75 is nearly half-metallic. The calculated magnetic moment per substituted transition metal (TM) atom for half-metallic compounds is found to be 3 μB, whereas that of a nearly half-metallic compound is 2.29 μB. The analysis of band structure and density of states shows that the TM-3d states play a key role in generating spin-polarization and magnetic moment in these compounds. Furthermore, we establish that the p-d hybridization reduces the local magnetic moment of Co and enhances that of V from their free space charge value of 3 μB and creates small local magnetic moments on nonmagnetic Cd and S sites. The exchange constant N0α and N0β have been calculated to validate the effects resulting from exchange splitting process.
Solvothermal technique has been used for the synthesis of Fe-doped CdS nanorods (Cd1−xFexS) with (x = 0.0, 0.3, 0.5, 1.0, 1.5). Structural analysis carried out using X-ray diffraction reveals the formation of defect-free hexagonal phase of the CdS nanorods. Energy dispersive X-ray analysis confirms the presence of elements Cd, Fe and S in their stoichiometric ratio. Blue shift in the band gap, as compared to the bulk CdS, has been observed in UV–visible spectra. The decrease in the intensity of the photoluminescence peaks confirms the quenching of spectra upon Fe doping. Transmission electron microscopy, high-resolution transmission electron microscopy and selected area diffraction studies confirm the polycrystalline nature as well as growth of CdS nanorods along (112) plane. Magnetic study confirms the ferromagnetic nature of the synthesized nanorods. Magnetic saturation has been found to be 0.187, 0.300, 0.450, 0.675, 0.600 emu g−1, respectively, for undoped, 3, 5, 10, and 15 % Fe-doped CdS.
In this study, we have explored the structural, electronic, and magnetic properties of V-doped zincblende MgSe and MgTe compounds using density functional calculations. The Wu-Cohen generalized gradient approximation is used for optimizing the structural properties, while the modified Becke and Johnson local (spin) density approximation functional has been employed to compute the electronic and magnetic properties. The spin dependent band structures, electronic density of state, and magnetic moments calculated for V-doped MgSe and MgTe semiconductors exhibit occurrence of 100 % spin polarization at the Fermi level which confirms stable half-metallic ferromagnetism in these materials. The spin-down gaps and the half-metallic gaps are analyzed in terms of V-3d and Se-4p (Te-5 p) hybridization, where it is observed that the V-3dstates play a key role in generating spin polarization and the magnetic moment in these compounds. The exchange constants N
0αand N
0β have been calculated to demonstrate the effects resulting from exchange splitting process. Furthermore, spin-polarized charge density calculation is presented for elucidating the bonding nature, while pressure dependence of total magnetic moment for three concentrations of V-doped MgSe and MgTe are also discussed.
The electronic structure of non-transition-metal element (Be, B, C, N, O and F)-doped CdS is studied based on spin-polarized density function theory within the generalized gradient approximation. Our results show that the substitutional Be, B and C for S in CdS induces spin polarized localized states in the gap or near the valence band and generates local magnetic moments 2.0 μB, 3.0 μB and 2.0 μB with one dopant atom, respectively. Whereas doping with N, O and F in CdS does not induce spin polarization. It is found the magnetic states in these systems are related to the difference between the electronegativities of the dopant and the anion in the host. Long-range ferromagnetic coupling may occur in Be, B and C-doped CdS, which can be explained by the p–d exchange-like p–p coupling interaction involving holes.
The structural, electronic and magnetic properties of zincblende (ZB) Cd1−xVxSe for different values of x were investigated using the full-potential linearized augmented plane wave plus local orbital (FPLAPW+lo) method based on spin-polarized density functional theory (DFT). It was confirmed that for all values of x, the ferromagnetic (FM) state is more stable than antiferromagnetic (AFM) state. The results show that Cd0.25V0.75Se and Cd0.5V0.5Se compounds exhibit a half-metallic (HM) characteristic while Cd0.75V0.25Se has nearly a HM nature. The obtained HM band gaps with EV-GGA have been considerably improved with respect to PBE-GGA scheme. The analysis of density of states (DOSs) curves confirms the hybridization between V d and Se p states in all compounds. The total magnetic moments of Cd0.25V0.75Se and Cd0.5V0.5Se compounds are 3μB (integer values), confirming their HM characteristic. Finally, the robustness of half-metallicity with changing the lattice parameters of Cd1−xVxSe alloys was discussed.
We report the preparation of spin-coated nickel-doped zinc oxide nanocrystalline thin films using high-quality colloidal diluted magnetic semiconductor (DMS) quantum dots as solution precursors. These films show robust ferromagnetism with Curie temperatures above 350 K and 300 K saturation moments up to 0.1 Bohr magnetons per nickel. These results demonstrate a step toward the use of colloidal zero-dimensional DMS nanocrystals as building blocks for the bottom-up construction of more complex ferromagnetic semiconductor nanostructures.
In this paper, we report theoretical investigations of structural, electronic and magnetic properties of ordered dilute ferromagnetic semiconductors Cd1−xFexS with x=0.25, 0.5 and 0.75 in zinc blende (B3) phase using all-electron full-potential linear muffin tin orbital (FP-LMTO) calculations within the density functional theory and the generalized gradient approximation. The analysis of band structures, density of states, total energy, exchange interactions and magnetic moments reveals that both the alloys may exhibit a half-metallic ferromagnetism character. The value of calculated magnetic moment per Fe impurity atom is found to be 4μB. Moreover, we found that p–d hybridization reduces the local magnetic moment of Fe from its free space charge value of 4μB and produces small local magnetic moments on Cd and S sites.
For investigating the structural, electronic and magnetic properties of zincblende (ZB) Cd1−xVxTe (0≤x≤1), we have employed the Wu–Cohen generalized gradient approximation (WC-GGA) and the modified Becke and Johnson local density approximation (mBJLDA) functionals within the frame-work of spin polarized density functional theory (DFT). The former exchange-correlation parameterization scheme has been used for optimizing the equilibrium structural properties, while the electronic band structures, electron density of states (DOS) and charge densities are computed using both functionals and their performances are compared. Our results show that the electron spin polarization in unfilled V-3d orbitals gives rise to spin exchange splittings (Δx(d) and Δx(pd)) which is the cause of half metallic (HM) ferromagnetism in the V-doped CdTe as revealed by the computed DOS. Consequently, the nature of effective potential is more attractive in spin-down case rather than that in spin-up case. The total magnetic moment for each of the compounds under study is 3μB where the main contribution comes from the V atom, while the nonmagnetic sites Cd and Te are also bestowed with minor atomic magnetic moments due to Te-5p–V-3d hybridization. Furthermore, we calculated the exchange constants N0α and N0β to determine the conduction and valence band contributions in exchange splitting process. A comparison of the two functionals, considered in this work, shows that the mBJLDA provides a better description of the electronic structure especially of the ferromagnetic Cd1−xVxTe (0.75≤x≤1). Moreover, as compared to WC-GGA, the mBJLDA predicts high Curie temperatures in V-doped CdTe by providing significantly larger values of Δx(d), Δx(pd), N0α, N0β and, importantly, a quite wide HM gap.
Ab-initio calculations are performed to investigate the structural, electronic and magnetic properties of spin-polarized diluted magnetic semiconductors composed of II–VI compounds Cd1−xCoxX (X=S, Se, Te) at x=0.25. From the calculated results of band structure and density of states, the half-metallic character and stability of ferromagnetic state for Cd1−xCoxS, Cd1−xCoxSe and Cd1−xCoxTe alloys are determined. It is found that the tetrahedral crystal field gives rise to triple degeneracy t2g and double degeneracy eg. Furthermore, we predict the values of spin-exchange splitting energies Δx(d) and Δx(p−d) and exchange constants N0α and N0β produced by the Co 3d states. Calculated total magnetic moments and the robustness of half-metallicity of Cd1−xCoxX (X=S, Se, Te) with respect to the variation in lattice parameters are also discussed. We also extend our calculations to x=0.50, 0.75 for S compounds in order to observe the change due to increase in Co.
Theoretical calculations of Ga1-xMnxP and Ga1-xMnxAs (x = 0.125) in the zinc blende phase are presented. The electronic structure and magnetic properties of these compounds are calculated and their correlation is investigated with the lattice compressions. The results show that, both the compounds hold their half-metallic nature, conductor for spin up state and semiconductor for spin down state, with their lattice compressions up to certain critical lattice constants. An abrupt change in the electronic and magnetic properties is observed at these robust transition lattice constants (RTLCs). These compounds loss their integer magnetic moments (4 μβ) and tremendous decrease in the bandgaps (spin down states) start at these critical lattice constants and hence the materials transform from half-metals to degenerate semiconductors. The calculated RTLC for Ga0.875Mn0.125P is 5.14 Å and for Ga0.875Mn0.125As is 5.25 Å. The possible compression in the lattice constants from their relaxed states, while maintaining their half-metallic nature, is up to 6% for Ga0.875Mn0.125P and 8% for Ga0.875Mn0.125As. The feasibility of the growth of these compounds on different substrates on the basis of the variation in the lattice constants is also discussed.
The effects of Co addition on the properties of Ni8−xMn4Ga4Cox ferromagnetic shape memory alloys are systematically investigated by first-principles calculations. The formation energy results indicate that the added Co preferentially occupies the Ni sites in Ni2MnGa alloy. The total energy difference between the paramagnetic and the ferromagnetic austenite plays an important role on the Curie transformation. The electronic density of states gives rise to the difference in the magnetic properties.
Colossal magnetoresistance - a huge decrease in resistance in response to a magnetic field has recently been observed in manganese oxides with perovskite structure. This effect is attracting considerable interest from both fundamental and practical points of view. In the context of using this effect in practical devices, a noteworthy feature of these materials is the high degree of spin polarization of the charge carriers, caused by the half- metallic nature of these materials; this in principle allows spin-dependent carrier scattering processes, and hence the resistance, to be strongly influenced by low magnetic fields. This type of field control has been demonstrated for charge-carrier scattering at tunnelling junctions and at crystal-twin or ceramic grain boundaries, although the operating temperature of such structures is still too low (≤150K) for most applications. Here we report a material-Sr2FeMoO6, an ordered double perovskite exhibiting intrinsic tunnelling-type magnetoresistance at room temperature. We explain the origin of this behaviour with electronic-structure calculations that indicate the material to be half-metallic. Our results show promise for the development of ordered perovskite magnetoresistive devices that are operable at room temperature.
Seismology provides a powerful tool for probing planetary interiors, but it has been considered inapplicable to tectonically inactive planets where earthquakes are absent. Here, however, we show that the atmospheres of solid planets are capable of exerting dynamic pressure on their surfaces, thereby exciting free oscillations with amplitudes large enough to be detected by modern broad-band seismographs. Order-of-magnitude estimates of these forces give similar amplitudes of a few nanogals for the Earth, Venus and Mars despite widely varying atmospheric and ambient conditions. The amplitudes are also predicted to have a weak frequency dependence. Our analysis of seismograms, recorded continuously from 1992 to 1993 at 13 globally distributed stations, shows strong evidence for continuously excited fundamental-mode free oscillations on the Earth. This result, together with other recent studies, is consistent with our estimate of atmospheric forcing and we therefore propose that it may be possible to detect atmospheric excitation of free oscillations on Venus and Mars as well.
The electronic structure and the ferromagnetism of CrS and CrP in the zinc-blende (ZB) phase are investigated by spin-polarized calculations with first-principles plane-wave pseudopotential method within the generalized gradient approximation for the exchange-correlation potential. From the analysis of the spin-dependent density of states, band structure and magnetic moment, we predict that ZB CrS and CrP at their respective equilibrium lattice constant are half-metallic ferromagnets with a magnetic moment of 4.00 and 3.00μB per formula unit, respectively. We also find that the ZB CrS maintains half-metallic ferromagnetism up to 3% compression of lattice constant while the half-metallic ferromagnetism for ZB CrP exists only near its equilibrium lattice constant.
The electrical properties of nonirradiated and electron irradiated structures, containing a polycrystalline thin layer of CdS, sandwiched between two gold electrodes, were investigated. The thin films of CdS, obtained through thermal-vacuum evaporation on the glass substrate at a temperature of 220 °C, were subjected to two sessions of irradiation with 7 MeV electrons to the fluences of 4×10<sup>15</sup> and 6×10<sup>15</sup> e/cm <sup> 2 </sup>, respectively. In the case of nonirradiated structures, under low voltages, the Ohm’s law is followed with a thermally activated electron concentration of n<sub>0</sub>≅3×10<sup>16</sup> cm <sup> -3 </sup>, an electron mobility μ<sub>0</sub>≅0.1 cm <sup> 2 </sup> /V s and a room temperature electrical conductivity σ<sub>0</sub>≅4×10<sup>-4</sup> Ω<sup>-1</sup> cm <sup> -1 </sup>. In this range of voltage the electron irradiation induces a small increase in the activation energy of mobility, determining, of course, a small decreasing of the mobility. At high-applied voltage, there is a space-charge-limited conductivity controlled by a single trap level having the depth of E<sub>c</sub>-E<sub>t</sub>≅0.086 eV and the total trap concentration N<sub>t</sub>≅8.9×10<sup>15</sup> cm <sup> -3 </sup>. In this range of voltage, the electron irradiation modifies the trap distribution. After the first session of irradiation a uniform trap distribution appears and after the second session, an exponential trap distribution was induced in the band gap of CdS layer. All the i-
nduced trap distributions are characterized and their effect on the charge transport mechanisms is discussed. © 1998 American Institute of Physics.
Structural, optical and magnetic properties of CdS thin films with the addition of Co prepared by (i) spray pyrolysis of Cd1−xCoxS (x⩽0.10) thin films (Type 1) and (ii) Co diffusion doped CdS films (Type 2) were investigated. The undoped film has a hexagonal structure with a strong (1 1 2) preferred orientation. As the Co concentration in CdS is increased, the preferred orientation changes from (1 1 2) to (0 0 2) direction. X-ray photoelectron spectroscopy (XPS) analysis shows that Co atoms on the surface of films are found to be bounded either to S atoms or O atoms. Although most of the bindings of Co atoms include Co–O bondings, some of them replace the Cd atoms by making chemical bounds with S atoms. The transmittance spectra indicate the four characteristic absorption maxima at the wavelengths of 680, 685, 729 and 744 nm, which were not observed for the undoped CdS film. Band gap energy Eg decreases from 2.43 to 2.37 eV with increasing Co content from x=0 to 0.10. The Co-doped Cd1−xCoxS films grown by spray pyrolysis (Type 1) didnot show any sign of ferromagnetic behavior. However, the Co diffused CdS films (Type 2) have clear ferromagnetic loops.
Based on non-spin-polarized electronic band structure calculations, we examined why the electronic structure of a semi-Heusler compound ABX has the 18-electron band gap, why 17-and 19-electron ABX compounds can be weakly ferromagnetic based on the Stoner criterion, and how the ferromagnetism of the 22-electron ABX compounds differs from that of the 17- and 19-electron analogs. To a first approximation, the electronic structure of ABX with 18 or more valence electrons is described in terms of the d10 ion for B, the s2p6 ion for X, and the dn ion for A (n=0, 1 and 4 for the case of 18, 19 and 22 valence electrons, respectively). Even for a 17-electron ABX compound the d-electron count for the electronegative transition metal B is close to d10. The ferromagnetism of the 17- and 19-electron ABX compounds is explained in terms of the Stoner criterion, and that the 22-electron ABX compounds by the strong tendency for the d-electrons of the d4 ion to localize.
The band structure of Mn-based Heusler alloys of the C1b crystal structure (MgAgAs type) has been calculated with the augmented-spherical-wave method. Some of these magnetic compounds show unusual electronic properties. The majority-spin electrons are metallic, whereas the minority-spin electrons are semiconducting.
We studied the structural, spin-polarized electronic band structures, density of states, and magnetic properties of the diluted magnetic semiconductors (DMSs) Cd(1-x)Mn(x)S and Cd(1-x)Mn(x)Se in zinc blende phase (B3) with 25% Mn by using the ab initio method. The calculations were performed by using the full potential linearized augmented plane wave plus local orbitals (FP-L/APW+lo) method within the spin-polarized density functional theory and the local spin density approximation (LSDA). Calculated electronic band structures and the density of states of these DMSs are discussed in terms of the contribution of Mn 3d(5)4s(2), Cd 4d(10)5s(2), S 3s(2)3p(4), and Se 4s(2)4p(4) partial density of states and we also compute the local magnetic moments. We estimated the spin-exchange splitting energies, Delta(x)(d) and Delta(x)(p-d), produced by the Mn 3d states, and we found that the effective potential for the minority spin is more attractive than that for the majority spin. We determine the s-d exchange constant N(0)alpha and p-d exchange constant N(0)beta, which resembles a typical magneto-optical experiment. The calculated total magnetic moment is found to be 5.0020 and 5.00013 mu(B) for Cd(1-x)Mn(x)S and Cd(1-x)Mn(x)Se, respectively. These values indicate that every Mn impurity adds no hole carriers to the perfect CdS and CdSe crystals. Moreover, we found that p-d hybridization reduces the local magnetic moment of Mn from its free space charge value of 5.0micro(B) and produces small local magnetic moments on the nonmagnetic Cd and S sites.
Ferromagnetism in manganese compound semiconductors not only opens prospects for tailoring magnetic and spin-related phenomena
in semiconductors with a precision specific to III-V compounds but also addresses a question about the origin of the magnetic
interactions that lead to a Curie temperature (T
C) as high as 110 K for a manganese concentration of just 5%. Zener's model of ferromagnetism, originally proposed for transition
metals in 1950, can explain T
C of Ga1−
xMnxAs and that of its II-VI counterpart Zn1−
xMnxTe and is used to predict materials with T
Cexceeding room temperature, an important step toward semiconductor electronics that use both charge and spin.
Finding a means to generate, control and use spin-polarized currents represents an important challenge for spin-based electronics, or 'spintronics'. Spin currents and the associated phenomenon of spin accumulation can be realized by driving a current from a ferromagnetic electrode into a non-magnetic metal or semiconductor. This was first demonstrated over 15 years ago in a spin injection experiment on a single crystal aluminium bar at temperatures below 77 K. Recent experiments have demonstrated successful optical detection of spin injection in semiconductors, using either optical injection by circularly polarized light or electrical injection from a magnetic semiconductor. However, it has not been possible to achieve fully electrical spin injection and detection at room temperature. Here we report room-temperature electrical injection and detection of spin currents and observe spin accumulation in an all-metal lateral mesoscopic spin valve, where ferromagnetic electrodes are used to drive a spin-polarized current into crossed copper strips. We anticipate that larger signals should be obtainable by optimizing the choice of materials and device geometry.
Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics. Comment: invited review, 36 figures, 900+ references; minor stylistic changes from the published version
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