First Principles Study on the Effects of Cu Doping on the Magnetic Moment and Electronic Properties of V-Doped ZnO

The CASTEP program was used to study the effects of Cu on the structure, magnetic moment and electronic properties of V-doped ZnO. The calculated enthalpies showed that the Cu atoms were inclined to stay near the V atoms. Cu neutralized the delocalized electrons in V-doped ZnO. Cu also suppressed the magnetic moments of Zn and O more than those of the V ions. The different amounts of suppression caused the moments to concentrate on the V atoms. The magnetic moments decreased in Cu and V co-doped ZnO. The suppressions of the magnetic moments and concentrations of the Cu atoms were verified with density of states calculations. The states showed that Cu increased the conduction in V-doped ZnO. The calculated spin isospheres showed that Cu improved the concentration of the magnetic moments on the V sites. The improved concentration enhanced the performance of diluted magnetic semiconductors based on V-doped ZnO. These results help in understanding the role of Cu in V-doped ZnO. They also provide a reference for preparing diluted magnetic semiconductors based on V-doped ZnO     

Vanadium doping on magnetic properties of H-passivated ZnO nanowires

A comprehensive theoretical investigation on the electronic and magnetic properties of V-doped and H-passivated ZnO nanowires (NWs) was performed using spin-polarized density functional theory. The magnetic couplings of six configurations of V-doped ZnO NWs are studied in detail and stable ferromagnetism (FM) ordering is found in certain configurations. The FM mechanism originated from the strong hybridization of V 3d and O 2p around the Fermi level. Our results show that the uniaxial strain is an effective method to tune the magnetic properties of this material system. Room temperature ferromagnetism in these V-doped ZnO NWs indicates that these materials have a promising application in nanoscale spintronics.     

Theoretical Investigation of Structural,Electronic, and Magnetic Properties of V-Doped MgSe and MgTe Semiconductors

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 ₀ αand N ₀ β 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.     

First Principles Study of Half-Metallic and Magnetic Properties of V Doped MgSiN2 Chalcopyrite

The electronic structure and magnetic properties of the V-doped magnesium silicon dinitride MgSiN₂ semiconductor have been studied by employing the first-principles method based on the density functional theory. The results indicate V-doped MgSiN₂ to be ferromagnetic for V_Mg (V substitutes Mg site) and V_Si (V substitutes Si site). Calculated total magnetic moments are 3.0 μ _B for V_Mg and 1.0 μ _B for V_Si per supercell, and the magnetic moment mainly arises from the V dopant. Density of states and band structures studies show half-metallicity for V-doped MgSiN₂ together with the half-metallic gap 0.74 and 0.36 eV for V_Mg and V_Si, respectively.     

Half-metallic ferromagnetism in Cd1−xTMxSe (TM = Cr, V and Mn) semiconductors

Electronic structures and magnetic properties of transition-metal-doped ternary systems based on zinc-blende CdSe compound are systematically explored using first-principles full-potential lineralized augmented plane-wave method. From the analysis of the spin-dependent density of states, band structure and magnetic moments, half-metallic ferromagnetism is obtained in the Cr- and V-doped systems with an integer value of 3μ_B and 4μ_B per unit cell for μ/x ratio, whereas Mn-doped systems show magnetic semiconducting character with a magnetic moment 5μ_B per unit cell. Half-metallic ferromagnetism comes mainly from spin-polarization of electrons in TM-d orbitals. It is also noted that the half-metallic gaps are increased with increasing TM (TM = Cr, V and Mn) concentrations, which make these materials possible candidates for spin injection in spintronic devices.     

Structural and electrical properties of V-doped ZnO prepared by the solid state reaction

This paper reports the synthesis, crystal structure and electrical conductivity properties of vanadium (V)-doped zinc oxide (ZnO) powders (i.e. Zn_1?2X V _X O binary system, x = 0, 0.0025, 0.005, 0.0075 and in the range 0.01 ≤ x ≤ 0.15). I-phase samples, which were indexed as single phase with a hexagonal (wurtzite) structure in the V-doped ZnO binary system, were determined by X-ray diffraction (XRD). The limit solubility of V in the ZnO lattice at this temperature is 3 mol % at 950 °C. The impurity phase at 950 °C was determined as ZnV₂O₆ when compared with standart XRD data. The research focused on single I-phase ZnO samples which were synthesized at 950 °C because of the limit of the solubility range is widest at this temperature. It was observed that the lattice parameters a and c decreased with V doping concentration. The electrical conductivity of the pure ZnO and single I-phase samples were studied using the four-point probe dc method at temperatures between 100 and 950 °C in an air atmosphere. The electrical conductivity values of pure ZnO and 3 mol % V-doped ZnO samples at 100 °C were 2.75 × 10^?6 and 7.94 × 10^?5 Ω^?1 cm^?1, and at 950 °C they were 3.4 and 54.95 Ω^?1 cm^?1, respectively. In other words, the electrical conductivity increased with V doping concentration.     

ZnO Film UV Photodetector with Enhanced Performance: Heterojunction with CdMoO4 Microplates and the Hot Electron Injection Effect of Au Nanoparticles

A novel CdMoO₄–ZnO composite film is prepared by spin‐coating CdMoO₄ microplates on ZnO film and is constructed as a heterojunction photodetector (PD). With an optimized loading amount of CdMoO₄ microplates, this composite film PD achieves a ≈18‐fold higher responsivity than pure ZnO film PD at 5 V bias under 350 nm (0.15 mW cm⁻²) UV light illumination, and its decay time shortens to half of the original value. Furthermore, Au nanoparticles are then deposited to modify the CdMoO₄–ZnO composite film, and the as‐constructed photodetector with an optimized deposition time of Au nanoparticles yields an approximately two‐fold higher photocurrent under the same condition, and the decay time reduces by half. The introduced CdMoO₄ microplates form type‐II heterojunctions with ZnO film and improve the photoelectric performance. The hot electrons from Au nanoparticles are injected into the CdMoO₄–ZnO composite film, leading to the increased photocurrent. When the light is off, the Schottky barriers formed between Au nanoparticles and CdMoO₄–ZnO composite film block the carrier transportation and accelerate the decay process of current. The study on Au‐nanoparticle‐modified CdMoO₄–ZnO composite film provides a facile method to construct ZnO film based PD with novel structure and high photoelectric performance.     

Enhanced ferromagnetism in ZnO nanoribbons and clusters passivated with sulfur

Inspired by recent experimental results, the electronic and magnetic properties of sulfur-passivated ZnO clusters and zigzag nanoribbons have been studied using first principles calculations in the framework of the local spin density approximation. In the case of the ZnO nanoribbons, the sulfur atoms or thiol groups were attached in different ways to the zinc or oxygen atoms located at the edges, whereas in clusters, the sulfur atoms were set on the surface, mainly interacting with atoms with low-coordinate number. After an exhaustive atomic relaxation, we found that a magnetic moment emerges in zigzag nanoribbons both with and without sulfur-passivation on the edges. However, the magnitude of the magnetic moment is very sensitive to sulfur passivation. In particular, we found that when sulfur is attached to the zinc atoms in an alternating fashion along the ribbon edges, the magnetic moment is a maximum (1.4 μ_B/unit cell). In the case of clusters, we found that the Zn₁₅O₁₅ cluster exhibits a high spin moment of 5.5 μ_B when capped with sulfur atoms. Our calculations indicate that sulfur-passivating of ZnO nanosystems could be responsible for recently observed ferromagnetic responses. This article is published with open access at Springerlink.com     

Nitrogen effect on spin-coated ZnO-based p–n homojunctions: structural,optical and electrical characteristics

In this work, ZnO:Al–N/ZnO:Al and ZnO:Ag–N/ZnO:Al homojunctions were deposited by means of spin coating method using precursors obtained by sol gel chemistry. The optical, structural and electrical properties of spin coated undoped and M-doped ZnO thin films (M?=?Al, Ag–N and Al–N) using ammonium hydroxide as a nitrogen source are reported. The films showed the wurtzite type structure with a c-axis (002) preferential orientation. The films showed a surface morphology consisting of wrinkles, which were constituted of nanocrystals in the range of ～?20 nm. The thin films were highly transparent in the visible region of the electromagnetic spectrum. The optical band gap of the films was close to 3.30 eV. Hall Effect measurements indicated that undoped and Al doped ZnO thin films showed an n-type conductivity, whereas ZnO:Al–N and ZnO:Ag–N thin films exhibited p-type conductivity, probably related to the formation of dual acceptor complexes related to nitrogen. Two types of p–n homojunctions (ZnO:Al–N/ZnO:Al and ZnO:Ag–N/ZnO:Al) were fabricated by means of sol–gel spin-coating method. In both cases, a rectifying behavior was observed, as revealed by current–voltage measurements.     

Spin Dynamics in ZnO-Based Materials

In this work, we address the issue of spin relaxation and its relevance to spin detection in ZnO-based materials, by spin-polarized, time-resolved magneto-optical spectroscopy. We have found that spin relaxation is very fast, i.e. about 100 ps for donor bound excitons in wurtzite ZnO, despite of a weak spin–orbit interaction. We also reveal that alloying of ZnO with Cd enhances spin relaxation, prohibiting ZnCdO/ZnO structures for efficient optical spin detection. On the other hand, a variation in strain field induced by lattice mismatch with substrates does not seem to lead to a noticeable change in spin relaxation. The observed fast spin relaxation, together with the limitation imposed by the band structure, are thus identified as the two most important factors that limit the efficiency of optical spin detection in the studied ZnO-based materials.     

Au–ZnO Nanocomposite Films for Plasmonic Photocatalysis

Nanocomposites based on plasmonic nanoparticles and metal‐oxide semiconductors are emerging as promising materials for conversion of solar energy into chemical energy. In this work, a Au–ZnO nanocomposite film with notably enhanced photocatalytic activity is successfully prepared by a single‐step process. Both ZnO and Au nanoparticles are synthesized in situ during baking of the film spin‐coated from a solution of Zn(CH₃COO)₂ and HAuCl₄. Furthermore, it is shown that this precursor solution can be formulated as a nanoink for the generation of micropatterns by microplotter printing, opening the way for the miniaturization of devices with enhanced properties for photocatalysis, optoelectronics, and sensing. The study demonstrates that Au–ZnO films exhibit 4.5‐fold enhanced photocatalytic properties for the decomposition of methyl orange upon sunlight exposure in comparison with ZnO films. Au nanoparticles improve significantly the photocatalytic activity of ZnO because they act as photosensitizers, absorbing photons at the localized surface plasmon resonance range (500–600 nm) and transferring electrons to the nearby ZnO semiconductor. XPS analysis of the Au–ZnO nanocomposite supports this explanation, indicating strong interactions between Au and ZnO.     

Study of the Structural,Electronic, Magnetic,and Optical Properties of Mn<Subscript>2</Subscript>ZrGa Full-Heusler Alloy: First-Principles Calculations

In this work, the structural, electronic, magnetic, and optical properties of Mn₂ZrGa full-Heusler alloy were investigated by using density functional theory (DFT) calculations. It is found that the spin-up states have a metallic character, but the spin-down bands have a pseudo-gap at the Fermi level. The total spin magnetic moment of Mn₂ZrGa (per formula unit) is 3.00 µ _B at an equilibrium lattice parameter of 6.15 Å. The calculations show that Mn₂ZrGa is a ferrimagnetic with 81% spin polarization at equilibrium lattice parameter. The effect of lattice parameter distortion on the magnetic properties and spin polarization is also studied. It is found that the total magnetic moment preserves its value for a lattice parameter range of 5.96–6.30 Å. The decreasing of the lattice parameter leads to improvement of spin polarization. The real and imaginary parts of dielectric function and hence the optical properties including energy absorption spectrum, reflectivity, and optical conductivity are also calculated. The value of plasma frequency for spin-up and down electrons is located at 1.78 and 0.74 eV, respectively.     

Ferromagnetic properties,electronic structures,and formation energies of Zn vacancy monodoping and (Zn vacancy,Li) codoped ZnO by first principles study

Using the first-principles method based on the density functional theory, we investigated the ferromagnetic properties, electronic structures, and formation energies of Zn vacancy monodoping and (Zn vacancy, Li) codoped ZnO. The results indicate that both cases prefer the ferromagnetic ground state. It was found that the Zn vacancy defect brings a spin polarized state in the nearest neighbor oxygen atoms, and the magnetic moments mainly come from the O atoms surrounding the defect centers, which are different from the conventional diluted magnetic semiconductor. In addition, we found that the spin polarized oxygen atoms have a metallic feature in both spin states and the ferromagnetic exchange interaction among oxygen atoms is mediated by Zn 3d state. Furthermore, it was observed that the replacement of one Zn atom in the system of Zn₁₅O₁₆ by one Li atom can generate holes and reduce the formation energy of Zn vacancy, and then stabilizes the zinc vacancy-including system, resulting in a larger magnetic moment.     

A Comparative First-Principles Study of Fe-, Co- and FeCo-Doped ZnO with Wurtzite and Zinc Blende Structures

First-principles study of the electronic and magnetic properties of zinc-blende and wurtzite structures of Fe-, Co-, and FeCo-doped ZnO is presented. It is found that after doping, this diamagnetic material becomes ferromagnetic and half-metallic. It is also shown that the half-metallicity may be obtained for ZnFeO, ZnCoO, and ZnFeCoO. The analysis of the spin density reveals that the ferromagnetic phase is due to the ferromagnetic coupling between the p?Cd states. The effects of Fe on the magnetic properties of ZB and WZ Fe-doped ZnO compound have been investigated with the GGA calculations. In order to understand the role of Fe atom in the ferromagnetism, the density of states both in the presence and absence of Co doping, were calculated. The obtained results show the presence of coupling between Co and Fe atoms through the spin-split impurity band exchange mechanism. More importantly, the calculations show that the magnetic moment changes sensitively with the type of structure of ZnO, zinc-blende, or wurtzite. A discussion by comparing the results obtained in this study and the experimental results reported in the literature of similar systems show a very good agreement.     

Tunable Ferromagnetism and Thermally Induced Spin Flip in Vanadium-Doped Tungsten Diselenide Monolayers at Room Temperature

The outstanding optoelectronic and valleytronic properties of transition metal dichalcogenides (TMDs) have triggered intense research efforts by the scientific community. An alternative to induce long-range ferromagnetism (FM) in TMDs is by introducing magnetic dopants to form a dilute magnetic semiconductor. Enhancing ferromagnetism in these semiconductors not only represents a key step toward modern TMD-based spintronics, but also enables exploration of new and exciting dimensionality-driven magnetic phenomena. To this end, tunable ferromagnetism at room temperature and a thermally induced spin flip (TISF) in monolayers of V-doped WSe₂ are shown. As vanadium concentration increases, the saturation magnetization increases, which is optimal at ≈4 at% vanadium; the highest doping level ever achieved for V-doped WSe₂ monolayers. The TISF occurs at ≈175 K and becomes more pronounced upon increasing the temperature toward room temperature. The TISF can be manipulated by changing the vanadium concentration. The TISF is attributed to the magnetic-field- and temperature-dependent flipping of the nearest W-site magnetic moments that are antiferromagnetically coupled to the V magnetic moments in the ground state. This is fully supported by a recent spin-polarized density functional theory study. The findings pave the way for the development of novel spintronic and valleytronic nanodevices and stimulate further research.     

Synthesis, optical and field emission properties of three different ZnO nanostructures

Three different ZnO nanostructures: nanocherries, nanomultipeds and nanospindles were successfully synthesized by thermal evaporation method under different experimental conditions. The X-ray diffraction peaks indicate that these ZnO nanostructures prefer to grow along the c-axis. Photoluminescence (PL) spectra show that they are partially related to morphologies. Comparing the field emission (FE) measurements of the three ZnO nanostructures, we found that the nanocherries structure has the lowest turn-on and threshold field, 2.31 V/μm and 5.83 V/μm, respectively, for nanospindles and nanomultipeds structures, they are 2.82 V/μm and 6.57 V/μm, 3.13 V/μm and 7.35 V/μm, revealing that the nanocherries structure may be one of the promising candidates for field emission displays.     

Characteristic and magnetic properties of Ni1–xZnxFe2O4 ferrites

Ferrites are magnetic ceramic materials which have additional metallic ion in ferrous oxide compounds. Ferrites are usually classified as soft or hard ferrites. In this study, characteristics and magnetic properties of magnetic materials having NiO_1–xZnO_xFe₂O₄ structure were investigated. Mechanical mixing of high purity NiO, ZnO and Fe₂O₃ powders were done to obtain homogenous NiO_1–xZnO_xFe₂O₄ powder mixture for x = 0.15, x = 0.50 and x = 0.85. These powder mixtures were pressed using hydraulic press machine and then subjected to sintering at same temperatures of 1000 °C for 1 hour. Obtained specimens were analyzed with scanning electron microscopy (SEM) imaging and energy dispersive X‐ray fluorescence (EDXRF) technique for the investigation of structural analysis; magnetic properties were determined using vibrating sample magnetometer (VSM). However, effects of composition, specimens and Zn% element in magnetic materials after energy dispersive X‐ray fluorescence on maximum magnetic moment (M_s) were analyzed using Taguchi orthogonal array design of experiments technique. The study indicates that Zn% element is the main process parameter that has the highest statistical influence on maximum magnetic moment. However, another parameter, composition, also has a significant effect on maximum magnetic moment. Then, Zn‐content was found to have a significant influence on the magnetic properties of the system.     

Synthesis and optical properties of nanocrystalline V-doped ZnO powders

This paper reports the synthesis and optical properties of nanocrystalline powders of V-doped ZnO (i.e. Zn_0.95V_0.05O, Zn_0.90V_0.10O, and Zn_0.85V_0.15O) by a simple sol–gel method using metal acetylacetonates of Zn and V and poly(vinyl alcohol) as precursors. Structure of the prepared samples was studied by X-ray diffraction, FTIR spectroscopy, and selected-area electron diffraction (SAED) analysis. The morphology of the powders revealed by SEM and TEM was affected by the amount of V, causing the formations of both nanoparticles and nanorods in the Zn_0.95V_0.05O sample, nanorods in the Zn_0.90V_0.10O sample, and nanoparticles in the Zn_0.85V_0.15O sample. The optical properties of the samples were investigated by measuring the UV–VIS absorbance and photoluminescence spectra at room temperature. All the samples exhibited UV absorption at below 400 nm (3.10 eV) with a well-defined absorbance peak at around 364 nm (3.41 eV) and 288 nm (4.31 eV). The band gap of the V-doped samples shows a decrease with increasing V concentration. The photoluminescence spectra of all the samples showed a strong UV emission band at 2.98 eV, a weak blue band at 2.82 eV, a week blue–green band at 2.56 eV, and a weak green band at 2.34 eV, which indicated their high structural and optical quality.     

Structural,luminescence and magnetic properties of Mn doped ZnO thin films using spin coating technique

Manganese doped zinc oxide (ZnO) thin films were synthesized for various wt% doping of Mn using sol–gel spin coating technique. The effects of Mn doping on the structural, morphological, compositional, photoluminescence (PL) and magnetic behaviour of ZnO thin films were investigated. Although, Mn doping did not change the lattice constants of the films, the texture coefficient is found to be improved for the films having higher percentage of Mn doping. PL studies reveal that as doping concentration of Mn increases, the intensity of emission peaks corresponding to violet and blue colour increases and the peak position shifts slightly. The saturated magnetic moments are found to decrease with the increase in Mn doping and the reason for such behavior is discussed.     

Influences of unintentionally doped carbon on magnetic properties in Mn-N co-doped ZnO

Carbon impurities are usually unintentionally doped in N-doped ZnO when attempting to realize p-type conductivity by metal-organic chemical vapor deposition. Mn-N co-doping technique, which is developed to realize hole-mediated room temperature ferromagnetism in ZnO, may further enhance the carbon incorporation. In this work, two kinds of Mn-N co-doped samples, grown at low temperature (400 °C) and high temperature (600 °C), respectively, have been compared to study the influences of carbon impurities. In contrast to that found on N mono-doped ZnO, an enhanced incorporation of carbon impurities is observed in the high-temperature-grown Mn-N co-doped sample with the conductivity changed from p to n type. According to X-ray photoelectron spectroscopy measurement, the compensation effect from carbon impurities is applied to elucidate the origin of the conductivity transition. Correspondingly, superconducting quantum interference device measurement certainly shows a much smaller value of the saturation magnetization for the high-temperature-grown sample. A possible effect from carbon related complexes on magnetization is also proposed to explain the decrease of the magnetic moment from the view of weakened spin polarization induced by unintentionally incorporated carbon. This assumption is further supported by the first-principle calculation on the Mn-N co-doped ZnO system with carbon incorporation.