Doped ZnO System Research Articles

Tailoring structural and optical properties of ZnO system through elemental Mn Doping through First-principles calculations

In this study, band structure and optical properties of Manganese (Mn) doped ZnO are investigated adopting first-principles study calculations. It is observed that, by addition of Mn in ZnO crystal, the electrical properties like conductivity and dielectric function of material have been improved. The elastic constants for the elements are also calculated which shows that the element is stable after addition of dopant. The computational study is done on CASTEP and Material Studio. The ZnO system is simulated and atoms of Mn has been added replacing Zn atoms. The properties that studied are band structure and optics including conductivity, reflectivity, dielectric function, absorption and refractive index. Furthermore, this study also includes calculation of Elastic constants, XRD Spectra, Phonon dispersion and Temperature profile of doped ZnO systems. The computational study produced promising results and experimental approach can be adopted to reinforce the outcomes of this study.

Investigation of Site Dependent Donor-Acceptor (Al-N) Doping Effect into ZnO for Optoelectronic Applications

In this study, the density functional theory (DFT) is used to investigate the effect of the incorporation of Al (donor) in the Zn-site and N (acceptor) in the O-site of ZnO. The detailed theoretical study highlights the confirmation of p-type conductivity and bandgap (0.58 and 0.21 eV) narrowing exhibits in N- and (Al-N)-doped ZnO systems. p-type nature is explicitly observed by introducing acceptor bands at the top of the valance band (VB). Whereas, degenerate n-type conductivity is seen in Al-doped ZnO and a widened bandgap of 2.70 eV is attributed to Burstein-Moss (BM) effect. The calculated value of the effective mass of the (Al-N)-doped ZnO system is lower than that of the un-doped ZnO. Enhancement of the absorption and photoconductivity in the visible region for N- and (Al-N)-doped ZnO could be due to the availability of more density of states. Importantly, reflectivity, refractive index, transmittance, dielectric constants, and optical band gap have also been calculated. Higher transmittance of the samples suggested that these could be suitable for the window material of solar cells. The optical bandgap value supports the electronic bandgap value. Therefore, our finding would be helpful to design high-performance homo-junction based electronic and optoelectronic devices.

First-principles prediction of higher Curie temperature, metallic and half-metallic ferromagnetism in Zn1-x(Vx,Nix)O systems

The electronic and magnetic properties of Zn(V,Ni)O systems with 2.08 %, 4.16 %, 6.25 %, 8.3 %, and 12.5 % impurity concentrations were investigated based on ab initio simulations. The first-principles calculations were carried out using density functional theory and local spin density approximation by pseudopotential method. Analyzing the calculated density of states, the mechanism to stabilize the ferromagnetic phase in the 3d-metals doped ZnO systems is discussed. The analysis of the total density of states shows that the V-doped ZnO presents a metallic nature and Ni-doped ZnO exhibits a half-metallic character. First-principles calculations show that the stability of ferromagnetic or antiferromagnetic behaviors depends on impurity concentrations and impurity positions in related ZnO:V,Ni systems. Finally, we estimated and studied the Curie temperatures for V- and Ni-doped ZnO systems with different impurity concentrations. The Curie temperatures for VxZn1-xO and NixZn1-xO systems are higher than room temperature and these compounds are suitable ferromagnetic DMS materials for spintronic applications.

Novel strategies for the enhancement of the NIR emission in the Ca doped ZnO system: Doping with Cr or adding Sb2S3

We report two novel strategies to enhance the NIR emission in the ZnO:Ca system. In the first strategy, we synthesized ZnO:Ca nanoparticles using a wet chemical method and doped them with various concentration of Cr. SEM images showed that the ZnO:Ca,Cr nanoparticles had a grain-like morphology and their sizes increased from 33 to 110 nm after incrementing the Cr concentration from 4 to 17 mol%. The analysis by X-ray diffraction (XRD) revealed that he ZnO:Ca,Cr sample made with 4 mol% of Cr had a pure hexagonal phase but the other samples synthesized with Cr concentration above 11 mol% presented the hexagonal phase and a small content of Cr2O3 (<3%). Moreover, the photoluminescence (PL) spectra of these samples showed two main emission peaks in the blue and NIR regions (λexc = 265 and 365 nm). In particular, the ZnO:Ca,Cr sample made with 17 mol% of Cr had the strongest NIR emission in the 700–850 nm region and only this sample showed a prominent NIR emission peak at 805 nm. Moreover, the CIE maps showed that the emissions of the ZnO:Ca,Cr samples are located in the blue region under excitation at 265 nm, but it was tuned to the orange region under excitation at 365 nm. In the second strategy, different amounts of Sb2S3 was added during the synthesis of ZnO:Ca to form ZnO:Ca/Sb2S3 composites. In this case, we obtained different morphologies of grains, rod-like and sheet-like for Sb2S3 contents of 10, 28 and 34 wt%, respectively. In addition, the composites presented a mixture of hexagonal and orthorhombic phases, which corresponded to the ZnO and Sb2S3, respectively. The ZnO:Ca/Sb2S3 composites had NIR emissions peaks in the 650–800 nm region and their intensity increased with the content of Sb2S3. Furthermore, their visible emission was tuned from blue to orange-red or to cold white light according to the CIE maps. Overall, the best ZnO:Ca,Cr sample had 312% and 37% higher emission than the ZnO:Ca reference sample and the best ZnO:Ca/Sb2S3 composite (under 265 nm excitation), respectively. In general, XPS studies showed the existence of oxygen vacancy defects, which produced the visible-NIR emissions in all the samples. The strategies presented here for NIR emission enhancement are feasible at low cost and the NIR emissions produced here occur within the first biological window (700–1000 nm), which is of interest for biomedical applications.

Study of La Doping on the Electronic Structure and Magneto-Optical Properties of ZnO by GGA+U Method

Based on the density functional theory, the effect of rare-earth La doping at different concentrations on the electronic structure, optical properties, and magnetic properties of ZnO was calculated by using the GGA+U method under the condition of spin polarization. The calculation results show that the cell of a La-doped ZnO system is distorted, resulting in a formation energy less than zero, in which case it is easy to dope. After La doping, the band gap narrows, the Fermi level enters the conduction band, and the excess carriers induced by La atoms degenerate to form n-type degenerate semiconductor materials. In the visible light region, a blue shift in the optical absorption edge of the La-doped ZnO system causes an increased average static dielectric constant, stronger polarization ability, stronger binding ability on charges, and the photoconductivity of the doped ZnO system is improved. The magnetic moment of the La-doped ZnO system is zero, so it is not magnetic.

Single Crystalline Transparent Conducting F, Al, and Ga Co-Doped ZnO Thin Films with High Photoelectrical Performance.

Transparent conductive film (TCF) is a material that integrates electrical conductivity and optical transparency. It is widely used as an electrode material in thin-film solar cells. However, considerable progress is needed to facilitate its high performance and low-cost preparation. In this study, a preparation scheme for AlF3 and GaF3 co-doped ZnO (FAGZO) thin films was designed and implemented by magnetron sputtering (MS). The mutual restraint between the electrical properties and the wide-spectrum transmission performance of ZnO films was resolved. First-principles calculations showed that the doped ZnO system had n-type conductivity and that the most stable structure was the FO-AlZn-GaZn system. The experimental results verified the theoretical predictions. Single crystalline ZnO transparent conducting films (ZnO-TCFs) of high quality were achieved by MS. After rapid thermal annealing (RTA) treatment, the mobility reached 49.6 cm2/V s, and the resistivity decreased to 3.82 × 10-4 Ω cm. The AT was 90% between 380 and 1200 nm. Furthermore, the application of the prepared FAGZO film in perovskite solar cells (PSCs) has been verified. Compared to the reference indium tin oxide film, the PSCs using the FAGZO film showed higher JSC and power conversion efficiency. These results demonstrate that MS combined with anion and cation co-doping provides an effective means of exploring high-quality and high-performance ZnO-TCFs.

Structural, electrical and magnetic properties of Gd-doped and (Al, Gd) codoped ZnO films

Gd-doped and (Al, Gd) codoped ZnO films were prepared by ion implantation and radio frequency magnetron sputtering. The resulting Gd-doped and (Al, Gd) codoped ZnO films were investigated with respect to their structural, electrical and magnetic properties. Room temperature ferromagnetism was obtained for all the doped films and the magnetization shows carrier concentration-dependent behavior. Two different regions can be divided in light of carrier concentration in which the bound magnetic polaron model and carrier-mediated exchange mechanisms produce a marked effect respectively in establishing the long-range ferromagnetic order. The first principle calculations reveal that the magnetic moment of (Al, Gd) codoped ZnO is higher than that of Gd-doped ZnO, and the ferromagnetic states of doped ZnO systems are more stable in the near configuration. Our results confirm that appropriate electron doping can effectively enhance the magnetic moment of the Gd-doped ZnO by controlling its concentrations, which may pave ways for preparing DMS with high magnetic moment using rare earth and group III elements as dopants.

Effect of Yb concentration on the structural, magnetic and optoelectronic properties of Yb doped ZnO: first principles calculation

Density functional theory-based investigation of the electronic, magnetic, and optical characteristics in pure and ytterbium (Yb) doped ZnO has been carried out by the plane-wave pseudopotential technique with generalized gradient approximation. The calculated lattice parameters and band gap of pure ZnO are in good agreement with the experimental results. The energy band gap decreases with increasing Yb concentration. The Fermi level moves upward into the conduction band after doping with Yb, which shows the properties of an n-type semiconductor. New defects were created in the band-gap near the conduction band attributed to the Yb-4f states. The magnetic properties of ZnO were found to be affected by Yb doping; ferromagnetic property was observed for 4.17% Yb due to spin polarization of Yb-4f electrons. The calculated optical properties imply that Yb doped causes a blue shift of the absorption peaks, significantly enhances the absorption of the visible light, and the blue shift of the reflectivity spectrum was observed. Besides, a better transmittance of approximately 88% was observed for 4.17% Yb doped ZnO system. The refractive index and the extinction coefficient were observed to decrease as the Yb dopant concentration increased. As a result, we believe that our findings will be useful in understanding the doping impact in ZnO and will motivate further theoretical research.

Study on electronic structure and optical properties of doped ZnO system

In this paper, the electronic structure and photoelectric properties of P and Cu doped ZnO systems have been studied by Density functional theory method. The results show that the formation energies of ZnO-P-Cu, ZnO-P-2Cu, ZnO-P and ZnO-Cu systems decrease in turn Compared with the intrinsic ZnO system, the ZnO-P, ZnO-P-Cu, ZnO-P-2Cu and ZnO-Cu systems have higher activity, the band gap of ZnO-P and ZnO-P-2Cu systems is reduced, and the electron transition is easier. In the doped system, the peak of the dielectric function shifts to the left and increases, the absorption of the electron to the photon increases obviously, and the absorption spectrum appears red shift, from the calculated results, it can be concluded that P and Cu single-doped and co-doped ZnO have great influence on the electronic structure and optical properties of ZnO system, which provides a theoretical basis for further study of the influence of doping on the properties of ZnO.

Effects of triaxial strain on carrier activity, carrier lifetime, and absorption spectrum of (S, Se, Te) and 2 N Co-doped ZnO

The acceptor (N)-isovalent (S, Se, Te) elements that separately co-dope ZnO is a novel doping technology. However, the effects of triaxial strain on the photocatalytic performance and mechanism of doped systems are often neglected in experimental studies. Moreover, the influence of interstitial H on the doped ZnO system is not considered. This paper adopted first-principles and selected the appropriate strain range and step length. Assuming the equivalent effect of several strain points of tensile strain or compressive strain, we used simulation calculation to fit the complex strain problem in the actual process (such as doping, the strain problem caused by the difference of the lattice constant and thermal expansion coefficient of the substrate and the doping system), and then studied physical properties of the doped system. The planar wave ultrasoft pseudopotential + U method based on the first-principles generalized gradient approximation under the framework of density functional theory was used to calculate (S, Se, Te) and 2 N co-doped ZnO. The interstitial H-doped Zn36SO33N2 was studied as a representative ZnO system. Results showed that the binding energy of all doping systems under unstrained conditions was negative with a relatively high stability. The strain increased under tensile strain and compressive strain. As the formation energy of the doping systems increased, system stability decreased. Although the band gap of all compressive strain systems widened, impurities formed in the band gap, and valence band electrons absorbed photons of low energy to transition to the energy level of the impurities and then to the energy level of conduction band. The photoexcited electron-graded transitions induced the absorption spectrum to red-shift. The band gap of the system widened, whereas the band gaps of other tensile strain systems narrowed, except for when the tensile strain was 1%. However, regardless of whether the band gap of the tensile strain system became narrow or wide, the photoexcited electrons were still able to transition in stages. Hence, the absorption spectrum of the tensile strain system still red-shifted. The stability, activity, carrier separation, and lifetime of Zn36SHiO33N2 were relatively better than those of Zn36SO33N2 at 5% tensile strain. These properties make Zn36SHiO33N2 an ideal photocatalyst. This study provides a theoretical reference for the experimental design and preparation of novel ZnO photocatalysts.

Post-annealing effects on excitonic states and defects in nanostructured Ti-doped ZnO thin films

We study the effects of post-annealing treatments on excitonic states and defects of nanostructured Ti-doped ZnO thin films grown by room-temperature magnetron sputtering technique. Here, the as-grown samples were annealed by varying the annealing environment, time, and temperature. We found that the higher excitonic emission was at 600 °C under N2 environment for 30 min. The excitonic states are analyzed by using spectroscopic ellipsometry, photoluminescence, and ultraviolet-visible absorption spectroscopy. Through critical point analysis of the complex dielectric function from spectroscopic ellipsometry, the energy of exciton is redshifted from 3.49 eV to 3.36 eV and the increase of excitonic transition is observed upon the annealing treatment. The weak excitonic transition in the as-grown sample is mainly due to the oxygen vacancies that promote electronic screening effect. The contribution of oxygen vacancies is confirmed by the presence of green luminescence (∼2.5 eV) and space-charge-limited current regime from electrical properties measurements. This work is very important for tunable optoelectronic devices based on the doped ZnO system.

Ferromagnetism in p-block-element doped ZnO: An ab-initio approach

Magnetic and electrical properties of various p-block-elements (B, Al, Ga, C, Si, Ge, N, P and As) doped ZnO system has been studied using first principle approach. The source of the induced magnetic moment has been identified by analysing the spin polarized partial-density of states in all the cases. In most of the cases, the dopant element yield a significant amount of magnetic moment in ZnO system. The p-orbital-electrons of dopant are the primary source of magnetism along with a small contribution from oxygen atoms surrounding the dopants. The density of states calculations are supported by magnetization density distribution and Bader charge analysis. Investigation on spin-spin interaction reveals that the magnetism in B, C, N, Si, P, Ge and As-doped ZnO system favours ferromagnetic spin-ordering, while Al and Ga doped system does not.

Hydrogen induced changes of optical and magnetic properties of nanocrystalline Zn0.95Gd0.03M0.02O (M=Al,Mg): Experimental and DFT studies

This research work aims to study the effect of co-doping by Al3+ to increase the electronic charge carrier concentration inversely to Mg2+. Zn0.97Gd0.03O, Zn0.95Gd0.03Mg0.02O, and Zn0.95Gd0.03Al0.02O nanopowders were synthesised by simultaneous thermal co-decomposition of a mixture of cadmium and metal complexes, followed by hydrogenation at 350 and 600 °C. This study aimed at establishing the preparation conditions including hydrogenation that were essential for the creation of room temperature ferromagnetic order starting from the paramagnetic Gd-doped ZnO by using structural and electronic consequences of codoping with ions of Al or Mg. X-ray diffraction analysis confirms total doping of (Gd, Mg and Al) impurities into ZnO host lattice as well as the absence of secondary compounds/oxides in the synthesised solid solutions. The reflectance has been found to be significantly affected upon co-doping and hydrogenation, while the energy band gap decreases slightly; i.e. Eg = 3.23–3.00 eV. Magnetic measurements reveal that all the as-synthesised doped ZnO powders gained paramagnetic behaviour defeating the diamagnetic characteristic of ZnO, due to the presence of Gd ions with an effective magnetic moment in the range 8.04–7.12 μB. The hydrogenation in the present work conditions did not change the paramagnetic behaviour except for ZnO:Gd:Al-H, showing a partial a magnetic order overlapping with paramagnetic component, resulting in a coercivity of 170.2 Oe, remanence of 0.550 memu/g, and saturation magnetization of 2.14 memu/g. Therefore, the conditions including hydrogenation that were necessary to create FM ordering were determined.First-principles calculations indicate that the Gd doped ZnO systems own large spin polarized effect due to the interaction between Gd-f and O-p electrons. The Mg and Al dopants can modulate the values of magnetic moments.

Preparation of Fe doped ZnO thin films and their structural, magnetic, electrical characterization

Fe doped ZnO thin films having chemical composition of Zn(1-x)FexO (x = 0.0, 0.05, 0.10, 0.15, 0.20) from one molar concentration of precursor sol was synthesized over glass substrate by sol-gel spin coating method. The XRD analysis of the samples reveals the wurtzite ZnO crystallite size reduces from 18.2 nm to 11.4 nm with the increase in Fe content from x = 0 to 0.20. The cubic spinel ZnFe2O4 is identified in the XRD pattern of high (x = 0.20) Fe containing sample. FESEM micrographs reveal that the average particle size reduces from 49.41 to 27.72 nm with the increase in Fe content from x = 0 to 0.20. Whereas, SPM images show that increasing Fe content reduces surface roughness of the films. TEM analysis of Fe (x = 0.10) doped ZnO system supports the phase identification by XRD and particle size analysis by FESEM. The VSM analysis reveals magnetization (Mr) of the samples from the M-H curve. SQUID analysis reveals magnetic properties indicating the formation of room temperature ferromagnetic material (RTFM). The value of saturation magnetization increases from 0.01 to 1.1 emu/gm with the increase in Fe content from 0 to 0.20. Electrical conductivity measurement of the thin film sample using four probe technique indicates that films are semiconducting in nature with electrical resistance (R) of the films varying from 99.8 to 163.3 Ω with the increase in Fe doping concentration from 0 to 0.10.

Effects of stress and point defect on the physical properties of ZnO:Nd

The magnetism sources and mechanism of Nd doping and point defect are frequently controversial. To solve these controversies, ZnO supercell models with different doping modes of Nd were constructed, and the geometric structure optimization and energy calculation of the established models were calculated based on the generalized gradient approximation method of density functional theory. Calculation results indicated that the formation energy of Nd doped ZnO systems completely followed the sequence Zn15NdO16 > Zn15NdO15 > Zn14NdO16. For systems in which Nd doping and Zn vacancy coexist, a strong hybrid coupling electron exchange effect was present among the unpaired O-2p that was nearest to the Zn vacancy, the Zn-4 s orbit that was second nearest to the Zn vacancy, and the Nd-3d orbit. Therefore, the magnetism originated from the RKKY double-exchange interaction, which was based on the hole carriers in the complexus as the medium. In contrast with the Nd doping system, systems with coexisting Nd doping and O vacancy did not exhibit increased magnetism. Thus, the systems are worthless in designing and preparing dilute magnetic semiconductors. The magnetic moment of the systems with coexisting Nd doping and Zn vacancy was the largest. Thus, the systems are valuable in such design and preparation. The absorption spectra of Zn16NdiO16 and Zn15NdO16 were red shifted under the condition without stress, whereas the absorption spectrum of Zn15NdO16 with stress was blue shifted and the magnetic moment increased. The Curie temperature of Nd double-doped ZnO system was higher than room temperature when the Nd-Nd distance was the shortest.

Effect of heavy Ag doping on the physical properties of ZnO

The band structure, density of state and absorption spectrum of Zn[Formula: see text]Ag[Formula: see text]O (x = 0.02778, 0.04167) were calculated. Results indicated that a higher doping content of Ag led to a higher total energy, lower stability, higher formation energy, narrower bandgap, more significant red shift of the absorption spectrum, higher relative concentration of free hole, smaller hole effective mass, lower mobility and better conductivity. Furthermore, four types of model with the same doping content of double Ag-doped Zn[Formula: see text]Ag[Formula: see text]O (x = 0.125) but different manners of doping were established. Two types of models with different doping contents of double Ag-doped Zn[Formula: see text]Ag[Formula: see text]O (x = 0.0626, 0.0833) but the same manner of doping, were also established. Under the same doping content and different ordering occupations in Ag double doping, the doped system almost caused magnetic quenching upon the nearest neighbor –Ag–O–Ag– bonding at the direction partial to the a- or b-axis. Upon the next-nearest neighbor of –Ag–O–Zn–O–Ag– bonding at the direction partial to the c-axis, the total magnetic moment of the doped system increased, and the doped system reached a Curie temperature above the room-temperature. All these results indicated that the magnetic moments of Ag double-doped ZnO systems decreased with increased Ag doping content. Within the range of the mole number of the doping content of 0.02778–0.04167, a greater Ag doping content led to a narrower bandgap of the doped system and a more significant red shift in the absorption spectrum. The absorption spectrum of the doped ZnO system with interstitial Ag also shows a red shift.

Origin of magnetism probed through electron spin resonance studies in Zn1-xMnxO synthesized by chemical route

Nanocrystalline Zn1-xMnxO (0.005 ≤ x ≤ 0.02) shows room temperature ferromagnetic behaviour. The electron spin resonance spectra of Zn1-xMnxO (0.005≤ x ≤ 0.02) consist of a broad resonance line stemming from interacting spins and a set of hyperfine structure lines originating in the presence of the paramagnetic Mn2+ ions. The broad resonance lines and the observation of resonance at low field indicate the magnetic inhomogeneity of the sample. The ferromagnetic contribution coming from the cationic interaction like Zn2+-Zn2+, Zn2+-Mn2+ independently or through oxygen vacancies dominate over the paramagnetic behaviour of Mn2+-Mn2+ interaction and gives rise to ferromagnetic behaviour in Mn doped ZnO system.

Enhancement of room-temperature ferromagnetism and dielectric response in nanocrystalline ZnO co-doped with Co and Cu

Enhancement of ferromagnetic ordering and dielectric response in the nanoparticles of Co and Cu co-doped ZnO are the most important findings presented in this report. The co-doped nanoparticles of ZnO were prepared by hydrothermal method. Hydrothermal synthesis is an important preparation technique to establish one dimensional growth of the nanoparticles along the easy axis and this technique on the other hand improves the defect densities in the doped ZnO systems. XRD analysis of the undoped and co-doped ZnO nanoparticles confirms the presence of single phase hexagonal wurtzite lattice structure of ZnO without the signature of any impurity phases. Also, hydrothermally prepared rod like co-doped ZnO nanoparticles consist large number of defect centers at the surface and the presence of such defect centers were confirmed by the Raman and photoluminescence studies. The magnetic measurements of Co and Cu co-doped ZnO nanoparticles using SQUID magnetometer reveal the presence of magnetic ordering and the enhancement of the magnetization of the co-doped ZnO system at room temperature as compare to undoped/mono-doped ZnO nanoparticles. The presence of ferromagnetic ordering together with paramagnetic contribution in the Co and Cu co-doped ZnO sample was confirmed by the fitting of M-T curve using 3D spin wave model and Curie-Weiss law in the temperature range of ∼300 K down to ∼5 K. Our result suggests that the magnetic properties are strongly correlated to the structural defects and grain boundary defects. Also, the large dielectric response of the co-doped ZnO nanoparticles appears due to the trapping of the free charge carriers by the defect centers present at the surface of the rod like Co and Cu co-doped ZnO nanoparticles. These modulations as well as the enhancements of magnetic and dielectric response of the co-doped ZnO nanoparticles are very much useful for many magneto-dielectric device applications.

Microstructure and magnetic behavior of (Mg/Ni) co-doped ZnO nanoparticles

Abstract Zn 0.95−x Mg x Ni 0.05 O nanoparticles were synthesized using sol-gel technique by varying x values from 0.01 to 0.05 in step of 0.01. The annealing temperature was optimized and 4% Ar-H 2 gas was used for the annealing process to obtain single phase Zn 0.95−x Mg x Ni 0.05 O samples. The possible lost weights of samples in a wide temperature range for Zn 0.95−x Mg x Ni 0.05 O samples were investigated by differential thermal analysis and thermo gravimetric analysis. X-ray diffraction of Zn 0.95−x Mg x Ni 0.05 O samples exhibited single phase with annealing process under 4% Ar-H 2 gas at 450 °C. A structural distortion was revealed by replacing Zn 2+ by Mg 2+ and Ni 2+ due to the ionic radius difference which gave rise to a decrease in the crystallite size. The SEM images showed cluster shape distribution in quasi-spherical particles and were almost observed in all frames with agglomeration. Magnetization measurements were conducted at room temperature for all samples under the DC magnetic field for magnetization curves (M vs. H). The magnetization curves of Mg and Ni -doped ZnO systems exhibited a ferromagnetic behavior at room temperature.

Effect of two identical 3d transition-metal atoms M doping (M = V, Cr, Mn, Fe, Co, and Ni) on the structural, electronic, and magnetic properties of ZnO

The effects of the kinds (M = V, Cr, Mn, Fe, Co, and Ni) and separation distances (d = 3.252, 4.600, 5.635, 6.504, 7.273, and 8.607 A for (0, i = 1–6) configurations, respectively) of two identical 3d transition metal (TM) atoms M doping on the structural, electronic and magnetic properties of ZnO have been investigated by using spin-polarized first-principles calculations. The formation energies of two identical M atoms doped ZnO systems are lower under O-rich condition than under Zn-rich condition and the formation energy minimization shows the Mn-doped ZnO system is the easiest to form and there exists a clustering trend for two identical M dopants. The ferromagnetic coupling between two identical M atoms under double-exchange mechanism leads to V (0, i = 1–6), Cr (0, i = 1–6), Fe (0, 2), and Ni (0, i = 4–6) cases to be half-metal with integer total magnetic moments of 6, 8, 8, and 4 μB, respectively. Whereas, the antiferromagnetic coupling between two identical M atom under superexchange mechanism leads to Mn (0, i = 1–6) and Co (0, i = 1–6) cases as well as Fe (0, i ≠ 2) and Ni (0, i = 1–3) cases to be nonmagnetic semiconductor as well as nonmagnetic metal, respectively.