Magnetic Properties Of ZnO Research Articles

Green mediated approach to investigate the optical, structural, photocatalytic, magnetic and dielectric properties of Cr3+ doped ZnO nanoparticles for energy applications

Herein, the influence of Cr3+ dopant on the structural, morphological, optical, photocatalytic, dielectric and magnetic properties of ZnO was investigated for various applications. Pure ZnO and Cr3+ doped ZnO nanoparticles were synthesised by green mediated approach. The synthesised nanoparticles examined by using XRD, SEM, EDX, FTIR, PL, UV–Vis spectroscopy, dielectric and magnetic analysis. XRD confirmed the wurtizte hexagonal structure of synthesised samples and also revealed that the Cr didn't alter the structure of host ZnO. The FTIR analysis revealed the presence of Cr ions in ZnO structures. Doping of Cr ions improved the optical absorbance of ZnO and the optical band gap showed the blue shift with increasing concentration of Cr. The synthesised Cr doped nanoparticles show the outstanding photocatalytic efficiency under solar irradiation against MG pollutant dye. The dielectric constant (ε) improves and dielectric loss (tan (δ)) reduces at lower frequencies with increasing content of Cr. The AC conductivity for doped nanoparticles showed the increasing trend, especially for 4.5 % Cr doped ZnO nanoparticles. The ferromagnetic behavior at room temperature of Cr doped ZnO nanoparticles confirmed by VSM. The obtained results from all investigations make the Cr doped ZnO samples a potential choice for various applications such as, spin based electronic devices and energy storage devices.

Ab initio investigation of magnetic properties of metal doped ZnO-Buckyball structures

Magnetic properties of metal-doped ZnO buckyball ‘X@(ZnO-bb)’ structure have been investigated using first-principle density functional theory. Different structures of ZnO Buckyball, with the dopant atom X(Where X = Al, Ag, Fe, and Co) have been studied. To understand if the magnetic properties are arising fully due to the dopant atoms or because of the structural variation or intrinsic defects, the Zn and O atom is placed at the center of ZnO-bb, instead of other dopants. This study claims a novel ZnO-bb structure whose magnetic properties are reported for the first time, to the best of our knowledge. The change in the design of the structure, as well as the doping atom, led to variations in the magnetic properties of ZnO. A small amount of magnetic moment was observed in the ZnO-bb with non-magnetic dopant atoms like Al and Ag. Furthermore, a comparatively large amount of magnetic moments were observed with magnetic atoms like Co and Fe. The presence of a small amount of magnetic moment in the X@(ZnO-bb) structure unwraps a scope to further study this novel structure with different dopant atoms for various applications. A possible mechanism for the initiation of structure-based magnetism is also discussed. When the Zn or O atoms are placed at the center of ZnO-bb, a small amount of magnetic moment is observed in the O@(ZnO-bb) structure. This work systematically studies the magnetic properties in the ZnO-bb structure, which can be used for various applications like analog and digital data storage, magnetic therapy, and devices used in medical fields like MRI, etc.

Impact of Nd Doping on Electronic, Optical, and Magnetic Properties of ZnO: A GGA + U Study

The electronic, optical, and magnetic properties of Nd-doped ZnO systems were calculated using the DFT/GGA + U method. According to the results, the Nd dopant causes lattice parameter expansion, negative formation energy, and bandgap narrowing, resulting in the formation of an N-type degenerate semiconductor. Overlapping of the generated impurity and Fermi levels results in a significant trap effect that prevents electron-hole recombination. The absorption spectrum demonstrates a redshift in the visible region, and the intensity increased, leading to enhanced photocatalytic performance. The Nd-doped ZnO system displays ferromagnetic, with FM coupling due to strong spd-f hybridization through magnetic exchange interaction between the Nd-4f state and O-2p, Zn-4s, and Zn-3p states. These findings imply that Nd-doped ZnO may be a promising material for DMS spintronic devices.

Impact of Cr doping on the structure, optical and magnetic properties of nanocrystalline ZnO particles

The doping of Cr ions on the structure, optical and magnetic properties of ZnO have been investigated. Zn1−xCrxO (0 ≤ x ≤ 0.05) samples were prepared by the solution combustion method. Rietveld refined x-ray diffraction results reveal that all the samples are in a hexagonal structure. Transmission electron microscopy (TEM) revealed that the particle size was 48.2 ±2.1 nm, 29.4 ± 2.2 nm and 25.3 ± 2.1 nm for the Zn1−xCrxO with x = 0, 0.03 and 0.05, respectively. The band-gap decreases slightly from 3.308 ± 0.003 eV to 3.291 ± 0.003 eV with increase of Cr content from x = 0 to 0.05, respectively. The field-dependent magnetization M(μοH) measurements of ZnO and Cr-doped ZnO exhibit room temperature ferromagnetism (RTFM). Photoluminescence and electron paramagnetic resonance exhibits negatively charged zinc vacancies (VZn−) and singly ionized oxygen vacancies (Vo+) in ZnO and these defects are responsible for RTFM. And the VZn− accountable for RTFM in Cr-doped ZnO. EPR results confirmed that Cr3+ ions replaces the Zn2+ sites in the hexagonal ZnO. The observed long-range ferromagnetism ordering is explained based on the bound magnetic polaron (BMP) mechanism. This work elucidates the origin of RTFM in synthesized ZnO and Cr-doped ZnO.

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.

Control of inhomogeneity and magnetic properties of ZnO:Co films grown by magnetron sputtering using nitrogen

We experimentally report the control of structural inhomogeneity and magnetic properties of Co-doped ZnO films using nitrogen mediated-crystallization. The ZnO:CoN were grown on a silicon substrate at room temperature by RF-magnetron sputtering using nitrogen and followed by a post-annealing treatment for 3 hours at 400 °C, 600 °C, 800 °C and 1000 °C in the air. This method induces changes in inhomogeneity properties comprised by microstructure and stoichiometry of each film, which are confirmed by X-ray diffraction, thermal desorption, and X-ray fluorescence measurements. The difference in inhomogeneity has led to the transformation in the magnetic properties. Films annealed at 400 °C, which showed the highest inhomogeneity, exhibited superparamagnetic-ferromagnetic properties. In contrast, all the other films exhibited diamagnetic properties. Increasing the post-annealing temperature above 400 °C reduces inhomogeneities indicated by improved grain size, decreased impurities, and lattice parameters and stoichiometry of ZnO:CoN films approached those of pure ZnO. Our present results will contribute to control the inhomogeneity of ZnO:Co films to improve magnetic properties at room temperature.

Effect of Ar:O2 ratio on magnetic properties of ZnO:Y thin films

4 at.% Y-doped ZnO (4YZO) thin film was fabricated by RF magnetron sputtering, on Si(111) substrate upon varying Ar:O2 ratios (75:25, 50:50, and 40:60). The effect of Ar:O2 ratio on morphological, structural, magnetic, and optical properties of these films have been investigated in detail. The films orientated along the (002) diffraction plane were confirmed by X-ray diffraction pattern. The defect centres in the prepared films were analysed using visible band emission from Photoluminescence spectra which showed the presence of oxygen vacancy (VO+) and zinc interstitial (Zni+). The number of donor defects (VO+ and Zni+) in the films were reduced with an increase in O2 content. The vibrating sample magnetometer results indicated that 4 at.% Y-doped ZnO thin film deposited at an Ar:O2 ratio of 75:25 exhibited ferromagnetic property with a saturation magnetization value of 2.01 emu/cm3. The observed magnetic coercivity value of 500 Oe, makes it suitable for non-volatile magnetic memory storage applications. The films prepared using an Ar:O2 ratio of 50:50 and 40:60 showed a blend of paramagnetic and weak ferromagnetic behaviour. The donor defects present in the films were responsible for the ferromagnetism in 4YZO thin films. The magnetic properties of 4YZO thin films have been explained using the bound magnetic polaron (BMP) model.

Ab-initio and Monte Carlo studies of the structural, electronic and magnetic properties of V-doped ZnO compound

Realizing room-temperature ferromagnetic interactions in diluted magnetic semiconductors is a precondition for the future application of next-generation spin-based information technologies. However, finding effective strategies to alter the inherent magnetic coupling remains difficult. This paper aims to propose an approach for manipulating the ferromagnetism of (0.12%, 0.18%, 0.25%) V-doped ZnO (V-ZnO). The influence of V doping on the structural, electronic, and magnetic properties of ZnO is studied using first principles pseudo-potential plane wave method within the density functional theory (DFT). According to the first-principles calculations, the ferromagnetic ground state is maintained by a half-metallic electronic structure resulting from substantial hybridization between V-3d and O-2p electrons, and the calculations suggest that the ferromagnetism could be governed by the interactions between cluster spines in the VO4 tetrahedra. With the magnetic coupling strengths obtained by the green’s function method with the Wannier functions as a localized basis, the Monte Carlo simulation based on the Classical Ising model predicts the ferromagnetism of Zn1−xVxO (x = 0.12%, 0.18%, 0.25%) with Tc = 55 K, 165 K and 345 K. The observed results show that, as a diluted magnetic semiconductor, V-doped ZnO is an excellent candidate.

Structural, Morphological, Electronic Structural, Optical, and Magnetic Properties of ZnO Nanostructures.

ZnO nanostructures were grown on a Si(111) substrate using a vapor-liquid-solid (VLS) growth procedure (pristine ZnO) and annealed via a rapid thermal-annealing process in an argon atmosphere at 1100 °C (Ar-ZnO). The synthesized ZnO nanostructures were investigated through structural, electronic structural, morphological, optical, and magnetic characterizations. X-ray diffraction and selective area electron diffraction (SAED) measurements revealed that both samples exhibited the hexagonal wurtzite phase of nanocrystalline ZnO. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy carried out at the O K-edge inferred the presence of the intrinsic-defect states. Field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy images displayed the formation of ZnO nanostructures. The photoluminescence (PL) spectra demonstrated an emission band in the UV region along with an additional defect band in the visible region. PL spectral analysis confirmed the presence of intrinsic defects in Ar-ZnO nanowires, contributing to the enhanced emission in the visible region. The Raman spectra showed the characteristic band (434 cm-1) corresponding to the vibrational modes of hexagonal wurtzite ZnO, with an additional band attributable to intrinsic defects. DC magnetization measurements showed a ferromagnetic response in both samples with enhanced coercivity in Ar-ZnO (~280 Oe). In brief, both samples exhibited the presence of intrinsic defects, which are found to be further enhanced in the case of Ar-ZnO. Therefore, it is suggested that intrinsic defects have played an important role in modifying the optical and magnetic properties of ZnO with enhanced results for Ar-ZnO.

Effect of short-term heat treatment in the hydrogen on magnetic properties of ZnO:Mn nanocrystals

The magnetic properties of ZnO:Mn(2at%) nanocrystals synthesized by ultrasonic aerosol pyrolysis were studied. It has been established that short-term thermal treatment in hydrogen does not affect the magnetization of the synthesized sample, which had ferromagnetic and paramagnetic components. The sample, which underwent heat treatment in air at T = 850°C and acquired paramagnetic properties, after heat treatment in hydrogen again became ferromagnetic without a paramagnetic phase. It has been established by the EPR method that the structure of defects in the synthesized ZnO:Mn(2%) NCs is inhomogeneous. It changes after heat treatment in hydrogen. It is shown that the controlled thermal treatment of the samples, first in air and then in hydrogen, makes it possible to predictably change their magnetic properties. The results obtained are explained using the model of coupled magnetic polarons. During thermal treatment in hydrogen, the ratio of the number of oxygen vacancies Vo and interstitial Mn2+ ions changes in the samples.

Tuning the optical and magnetic properties of ZnO by Fe3O4

In this work, nanocomposites were prepared with different weight ratios based on the formula where x = 0.01, 0.03, 0.05, 0.07 and 0.09. The structure, morphology, optical, and magnetic properties were examined by x-ray diffraction, UV–vis-NIR diffuse reflectance spectroscopy, high-resolution transmission electron microscopy (HRTEM), and vibrating sample magnetometer (VSM). The x-ray diffraction (XRD) results confirm the phase purity formation of nanocomposites. The transmission electron microscopy (TEM) exhibited the prepared powders are nanoparticles with the spherical shapes of and nanorod for ZnO. UV–vis-NIR diffuse reflectance measurements showed that the modified the optical properties of ZnO. Results of the vibrating sample magnetometer (VSM) display a superparamagnetic characteristic of and ferromagnetic behavior for nanocomposites. The magnetization and remanence magnetization of nanocomposites increases with content.

First-principle study of the new mechanism of alkaline earth metals and point defects on the magnetic properties of ZnO

Negative monovalent oxygen ions exist in oxides apart from negative divalent oxygen ions. This condition shows that the double exchange interaction model based on the basic assumption that all oxygen ions are negative divalent ions needs to be corrected. This study used first principles to investigate the magnetic mechanism of point defects on the ZnO: Be/Mg/Ca system. Results show that the binding energy of the three systems of Zn34MHiO36 (VZn1−, M = Be/Mg/Ca) is relatively the smallest, and the doped system has the best stability. The magnetism comes from the itinerant electrons produced by negative monovalent oxygen ions, and the absolute value of total magnetic moment is 1μB. The doping system d0 ferromagnetism theoretically provides a new mechanism for the magnetic origin of nonmagnetic materials and offers a new idea for the preparation of magnetic semiconductor materials.

Dependence of Magnetic Properties of ZnO:Mn Nanocrystals on Synthesis Conditions

Dependence of Magnetic Properties of ZnO:Mn Nanocrystals on Synthesis Conditions

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.

Effect of Mn doping and point vacancy on stability and magnetism of ZnO

Understanding the source of magnetism in Mn doped ZnO (ZnO:Mn) is an active area of research, made difficult experimentally by the challenge of controlling point vacancies in ZnO:Mn. Therefore, the stability and magnetic properties of ZnO:Mn with point vacancies were studied by first-principles calculations based on density functional theory (DFT). Formation energy and magnetic moment calculation results show that Mn prefers to cluster in ZnO:Mn. This clustering can become uniformly distributed through modifications by Zn vacancies (V Zn ) or O vacancies (Vo). Magnetic analysis shows that Mn dopant in Zn site (ZnO:Mn Zn ) coupled with V Zn or interstitial Mn (Mn i ) coupled with V O makes ZnO having long-range ordered ferromagnetism (FM) and an increased Curie temperature ( Tc ) above room-temperature. The ZnO:Mn Zn with V Zn exhibits obvious half-metallic characteristics that are of essential benefit to the design and preparation of a new-type of spin-electron injection source dilute magnetic semiconductor. The magnetic sources of ZnO:Mn Zn with V Zn and Mn i -doped ZnO (ZnO:Mn i ) with V O arise from carrier-mediated magnetic interaction and the double exchange of Mn3d, O2p and Zn4s orbitals, consistent with the theories of average field approximation and the double exchange mechanism.

A review on defect related emissions in undoped ZnO nanostructures

Extraordinary interest has been gained in ZnO as an eminent host for dilute magnetic semiconductors because of its potential applications in optoelectronics, spin light emitting diodes, photovoltaics, photodetectors and solar cells. Its wide band gap of 3.3 eV and large exciton binding energy makes it potential material for spin light emitting diodes. The distribution and interaction of the native defects of ZnO play a major role in tailoring the optical and magnetic properties of ZnO. The redistribution of defects and their luminescence properties can be analysed with the help of Photoluminescence (PL) spectroscopy. This paper reviews the luminescence of intrinsic defects of ZnO and their emission in the PL spectrum.

Effect of different Mn doping and point vacancy ratios on the magnetic properties of ZnO

The magnetic source of Mn doping and Zn vacancy coexisting in ZnO is controversial. To solve this problem, this work used the generalized gradient approximation first-principles plane-wave ultrasoft pseudo potential + U method based on density functional theory to calculate the effect of different Mn doping to point vacancy ratios on the magnetic properties of ZnO. The formation energy of ZnO with different Mn-substituted Zn (MnZn) to oxygen/zinc vacancy (VO/VZn) ratios can be smaller and more stable in zinc (Zn)-rich conditions than in oxygen (O)-rich conditions. The ZnO system exhibits p-type half-metallic ferromagnetism when the MnZn to VZn ratio is 2:1 or 2:2. When the Mn doping amount is constant, the Zn vacancies increase and the total magnetic moment of the doped system decreases. For the ZnO system in which Mn doping and oxygen vacancies coexist, when the amount of oxygen vacancies is constant, with Mn doping increase, the magnetic moment becomes larger. Both Zn22Mn2O22 and Zn20Mn2O24 can achieve ferromagnetic characteristics above room temperature.

The effect of heat treatment on the magnetic properties of ZnO:Mn nanocrystals obtained by ultrasonic aerosol pyrolysis

The effect of heat treatment on the magnetic properties of ZnO:Mn nanocrystals obtained by ultrasonic aerosol pyrolysis

First-principles study of the effect of Mn and point vacancies with different valence states on the magnetic properties of ZnO

It is challenging to experimentally modulate the ferromagnetic properties of ZnO:Mn by point vacancies. Moreover, the magnetic source and magnetic mechanism of ZnO containing doped Mn and point vacancies, both with different valence states, have not been fully understood; using first principles can theoretically analyse this problem systematically. Therefore, in this study, the effects of different valence states of Mn and point vacancies on the magnetic properties of ZnO are calculated by first principles, revealing that ZnO:Mn has a lower formation energy and a more stable structure under oxygen-rich conditions than under zinc-rich conditions. Under oxygen-rich conditions, less Zn34Mn22+O35:VO0/1+/2+ and more Zn34Mn22+O36, Zn34Mn23+/4+O35:VO°, Zn33Mn22+O35:VZn0/1−/2−, and Zn33Mn23+/4+O36:VZn° are formed, facilitating the formation of a stable structure for the latter system compared to the others. The Zn33Mn22+O35:VZn° system not only possesses the lowest formation energy, but also the largest magnetic moment (10μB), indicating that a Zn vacancy allows the doping system to possess a high magnetic moment and also enhances the stability of the system. Therefore, Zn33Mn22+O35:VZn° is the most valuable of the systems studied. Analysis of the magnetic source and magnetic mechanism for this system revealed that the system possesses the magnetism and room temperature ferromagnetism, presents the characteristics of half-metallization, and that its magnetism is mainly derived from the itinerant electron and double exchange between O2p and Mn3d using holes as the medium. This is of great value for the design and preparation of new dilute magnetic semiconductors with high magnetic moments and high-Curie-temperature hole polarisation from 100 % injection sources.

Ab-initio, Monte Carlo and experimental investigation on structural, electronic and magnetic properties of Zn1-xNixO nanoparticles prepared via sol-gel method

In this work, structural, electronic and magnetic properties of Ni doped ZnO nanoparticles (NP’s) synthesized via the sol-gel method have been investigated. Different techniques of characterization have been applied to study the Ni dependence of the microstructural, morphological, compositional and magnetic properties. As a result, X-ray diffraction analysis indicates that the obtained samples have a hexagonal Wurtzite structure with preferential orientation along (101). The increase of Ni concentration leads to a size reduction of the nanoparticles. Also segregated Ni clusters have been observed by SEM/EDX. The magnetization field (M − H) curves reveal the existence of ferromagnetism in Ni-doped ZnO at room temperature. First principle calculations based on density functional theory are applied to study the effect of Ni doping on the structural, electronic and magnetic properties of ZnO, allowing for a deeper understanding for the experimental findings. The obtained results indicate that Ni doped ZnO with less than 8.33% Ni present long-range ferromagnetic ordering. Furthermore, Ni doped ZnO is antiferromagnetically stable at 12.5%. Monte Carlo simulation based on heat bath algorithm coupled with DFT results have been used to validate the proposed explanation for the magnetic behavior of the experimental part. Therefore, the obtained results indicate that Ni doped ZnO is a good candidate as a diluted magnetic semiconductor due to its high exchange coupling interaction that leads to a high Curie temperature.