Composition Zn0 Research Articles

Structural, electrical and magnetic behavior in high-temperature sintered Zn1–x Mn x O

Nanocrystalline Mn-doped ZnO of compositions Zn1–x Mn x O (0 ≤ x ≤ 0.08) has been synthesised by chemical route for uniform substitution of Mn in Zn site and then sintered at 1300 °C. Systematic investigations show the effect of Mn doping level and the sintering temperature on the structural, electrical and magnetic properties of ZnO. The average size of the nanocrystalline particles is in the order of 30–50 nm, whereas the grain sizes of the sintered specimen are of the order of few microns. Substitution of Mn in ZnO has been confirmed from the X-ray diffraction peak shift. A few peaks related to secondary phases of MnO have been observed in the X-ray diffraction patterns of the doped samples. ZnO and Mn-doped ZnO show Ohmic behavior and increased resistivity value with the increasing concentration of Mn. Effect of Mn concentration in ZnO has also been reflected in the dielectric constant and dielectric loss values. All the sintered samples show paramagnetic behavior even though the presence of MnO with oxygen vacancies is evident in X-ray photoelectron spectroscopic study.

Magnetic phase transitions in ferrite nanoparticles characterized by electron spin resonance

Ferrite magnetic nanoparticles in the composition Zn0.7Ni0.3Fe2O4 were synthesized by the polyol method, with an average size of 8 nm. Electron spin resonance (ESR) measurements were carried out at a frequency of 9.45 GHz in the 100–500 K temperature range. Obtained results exhibited a characteristic ESR signal in terms of resonance field, Hres, linewidth, ΔH, and peak ratio, R, for each magnetic phase. At low temperatures, the ferrimagnetic phase showed low Hres, broad ΔH, and asymmetric R. At high temperatures, these parameters exhibited opposite values: high Hres, small ΔH, and R ∼ 1. For intermediate temperatures, a different phase was observed, which was identified as a superparamagnetic phase by means of zero-field cooling-field cooling and hysteresis loops measurements. The observed differences were explained in terms of the internal fields and especially due to the cubic anisotropy in the ordered phase.

Photoluminescence and Raman studies for the confirmation of oxygen vacancies to induce ferromagnetism in Fe doped Mn:ZnO compound

With a motivation to compare the magnetic property, we synthesised undoped, transition metal (TM) Mn doped and (Mn:Fe) co-doped ZnO ceramics in the compositions ZnO, Zn0.98Mn0.02O and Zn0.96(Mn0.02Fe0.02)O. Systematic investigations on the structural, microstructural, defect structure and magnetic properties of the samples were performed. Low temperature as well as room temperature ferromagnetism has been observed for all our samples, however, enhanced magnetisation at room temperature has been noticed when ZnO is co-doped with Fe along with Mn. Particularly the sample with the composition Zn0.96Mn0.02Fe0.02O showed a magnetisation value more than double of the sample with composition Zn0.98Mn0.02O, indicating long range strong interaction between the magnetic impurities leading to higher ferromagnetic ordering. Raman and PL studies reveal presence of higher defects in form of oxygen vacancy clusters created in the sample due to Fe co doping. PL study also reveals enhanced luminescence efficiency in the co doped sample. Temperature dependent magnetisation study of this sample shows the spin freezing temperature around 39K indicating the presence of small impurity phase of Mn2−xZnxO3 type. Electron Spin Resonance signal obtained supports ferromagnetic state in the co doped sample. Enhancement of magnetisation is attributed to interactions mediated by magnetic impurities through large number of oxygen vacancies created by Fe3+ ions forming bound magnetic polarons (BMP) and facilitating long range ferromagnetic ordering in the co- doped system.

Enhancement of Two‐Dimensional Electron‐Gas Properties by Zn Polar ZnMgO/MgO/ZnO Structure Grown by Radical‐Source Laser Molecular Beam Epitaxy

A Zn polar ZnMgO/MgO/ZnO structure with low Mg composition Zn1−xMgxO layer (x = 0.05) grown on a‐plane (11–20) sapphire by radical‐source laser molecular beam epitaxy was reported. The insertion of a thin (1 nm) MgO layer between ZnMgO and ZnO layers in the ZnMgO/ZnO 2DEG structures results in an increase of 2DEG sheet density and affects electron mobility slightly. The carrier concentration reached a value as high as 1.1 × 1013 cm−2, which was confirmed by C‐V measurements. A high Hall mobility of 3090 cm2/Vs at 10 K and 332 cm2/Vs at RT was observed from Zn0.95Mg0.05O/MgO/ZnO heterostructure. The choice of the thickness of MgO was discussed. The dependence of carrier sheet density of 2DEG on ZnMgO layer thickness was calculated in theory and the theoretical prediction and experimental results agreed well.

Structural, Electrical, Optical and Magnetic Properties of Zn0.9Co0.1O, Zn0.9Ni0.1O, Zn0.9Co0.06Ni0.04O

Samples of composition Zn0.9Co0.1O, Zn0.9Ni0.1O, Zn0.9Co0.06Ni0.04O were prepared by powder metallurgy method. Structural property was studied by X-ray diffractometer (XRD), and Fourier transform infrared spectroscopy (FTIR). Magnetic, electrical and optical properties were studied by vibrating sample magnetometer (VSM), four point probe method and UV-Visible spectrophotometer, respectively. Single phase wurtize structure was obtained for Zn0.9Co0.1O and Zn0.9Co0.06Ni0.04O, while a secondary phase of NiO was found in Zn0.9Ni0.1O. The bandgap energy found in all samples was less than pure ZnO. Scanning electron microscope (SEM) studied surface Morphology. Moreover, room temperature ferromagnetism (RTFM) was observed for all samples.

Effect of Co and Cd Doping on Structural, Magnetic, Electrical and Optical Properties of ZnO Based Dilute Magnetic Oxide Semiconductor

Dilute magnetic oxide materials of composition Zn0.9Co0.1O, Zn0.9Cd0.1O and Zn0.9Co0.06 Cd0.04O were synthesized by Powder Metallurgy Method. Electrical, optical and magnetic properties were studied by Four Point Probe method UV- Visible Spectrophotometer, and Vibrating Sample Magnetometer (VSM) respectively. While, structural property was studied by X-ray diffraction (XRD), and Raman Spectroscopy. Single phase wurtize structure was found for Zn0.9Co0.1O, and Zn0.9Co0.06 Cd0.04O, but a secondary phase of CdO was obtained for Zn0.9Cd0.1O. UV-Vis spectroscopic results confirm the incorporation of the dopants in to the ZnO lattice structure as the band gap energy exhibited red shift. Room Temperature ferromagnetism (RTFM) was found for all the three samples.

Weak ferromagnetism and temperature dependent dielectric properties of Zn0.9Ni0.1O diluted magnetic semiconductor

In this study the room temperature ferromagnetic behaviour and dielectric properties of ZnO based diluted magnetic semiconductor (DMS) have been investigated using nominal chemical composition Zn0.9Ni0.1O. The X-ray diffraction analysis confirmed formation of single phase hexagonal wurtzite structure. An increase in grain size with increasing sintering temperature was observed from scanning electron microscopy. Field dependent DC magnetization values indicated dominant paramagnetic ordering along with a slight ferromagnetic behaviour at room temperature. Frequency dependent complex initial permeability showed some positive values around 12 at room temperature. In dielectric measurement, an increasing trend of complex permittivity, loss tangent and ac conductivity with increasing temperature were observed. The temperature dependent dispersion curves of dielectric properties revealed clear relaxation at higher temperature. Frequency dependent ac conductivity was found to increase with frequency whereas complex permittivity and loss tangent showed an opposite trend.

Novel Self‐Activated Zinc Gallogermanate Phosphor: The Origin of its Photoluminescence

Since 2012, zinc gallogermanate has drawn interests as an excellent host phosphor for a variety of dopants (e.g., Cr3+, Bi3+ and Mn2+). However, the origin of its self‐activated luminescence has been largely unknown. Here, zinc gallogermanate of the composition Zn1+xGa2−2xGexO4 (0 ≤ x ≤ 1) is prepared by solid‐state reaction, and the evolution of the crystal structure with the composition is studied. The phosphors show a broad white‐bluish emission upon excitation by ultraviolet (UV) light, and the luminescence intensity greatly increases as Ga3+ are substituted by Ge4+. A full spectrum of the defects and trap centers responsible for the luminescence is given by a multiple characterization methods, such as low temperature electron spin resonance, positron annihilation lifetime and thermoluminescence spectra. The results show that the zinc gallogermanate is a promising self‐activated phosphor for a variety of applications.

Investigation of Structural, Magnetic, and Optical Properties of ZnO Codoped with Co and Cd

Co and Cd have been codoped in ZnO using a simple solid state reaction technique to synthesize dilute magnetic oxide semiconductors of composition Zn0.9Co0.1−xCdxO (x = 0.0-0.1with an increment of 0.02). Hexagonal wurtzite structure has been obtained for samples up tox = 0.06, using X-ray diffractometry. However, atx = 0.08and 0.1, secondary peak of CdO is observed. Raman spectra of the samples have been obtained in 200–800 cm−1range. UV-VIS spectrophotometer is used to study the optical properties, which shows that band gap energy decreases with the increase in Cd concentration. A weak ferromagnetic behavior was evident which decreased further by adding Cd in the series. Room temperature resistivity measurements performed using four-point probe technique showed that their values lie in the semiconductor range. Structural morphology of the samples has been investigated by a scanning electron microscope and grain size has been determined. Raman spectra and Fourier transform infrared spectroscopy revealed the successful incorporation of Co and Cd ions into the host ZnO lattice.

Growth and structural, optical, and electrical properties of zincite crystals

An X-ray diffraction study of ZnO crystals grown by the hydrothermal method has revealed reflections that give grounds to assign them to the sp. gr. P3 rather than to P63mc. The distribution of Zn1, Zn2, O1, and O2 over structural positions, along with vacancies and incorporated zinc atoms, explains the dissymmetrization observed in terms of the kinetic (growth) phase transition of the order-disorder type, which is caused by ordering Zn and O atoms over structural positions. The color of crystals of refined compositions (Zn0.975□0.025)Zni(0.015)(O0.990□0.010) (green) and (Zn0.965□0.035)Zni(0.035)O (bright green) is related to different oxygen contents, which is confirmed by the results of electron probe X-ray microanalysis and absorption spectroscopy. The degree of the structural quality of crystals, their resistivity, and activation energy are also related to oxygen vacancies.

Absence of room temperature ferromagnetism in Mn-doped ZnS nanocrystalline thin film

Mn-doped ZnS nanocrystalline thin films having composition Zn1−xMnxS (x=0.02, 0.05, 0.1 and 0.15) were prepared by the electron beam evaporation technique. Their structural and magnetic properties had been investigated. X-ray diffraction results show single phase of hexagonal type structure samples without any detectable secondary phase providing the evidence that Mn2+ ions are incorporated into the ZnS lattice. Evidence of nanocrystalline nature of the films was observed from the investigation of surface morphology using atomic force microscopy. The magnetic measurements at 5K reveal superparamagnetic behavior. The field dependent magnetization measurements confirm the absence of the room temperature ferromagnetism in the single phase electron beam evaporated Zn1−xMnxS (x=0.02, 0.05, 0.1 and 0.15) nanocrystalline films. Furthermore, the inverse susceptibility versus T confirms paramagnetic behavior for the Mn-doped films in the temperature range 100K≤T≤300K. The absence of significant impurities and/or defects could be attributed to explanation for the absence of free carriers and consequently the absence of room temperature ferromagnetism in all nanocrystalline Zn1−xMnxS films. The absence of room temperature ferromagnetism is evidence by marked concave nature of Arrott's plot without any spontaneous magnetization.

Effect of doping concentration on absorbance, structural, and magnetic properties of cobalt-doped ZnO nano-crystallites

Abstract Controlled conduction of magnetic spins is desired for data processing in modern spintronic devices. Transition metal-doped ZnO is a potential candidate for this purpose. We studied the effects of cobalt doping on structural, absorbance, and magnetic properties of ZnO nano-particles. Different compositions (Zn0.99Co0.1O, Zn0.97Co0.3O, and Zn0.95Co0.5O) of cobalt-doped ZnO were fabricated using metallic chlorides by co-precipitation method. XRD revealed standard ZnO wurtzite crystal structure without lattice distortion due to impurities but showed presence of additional phases at higher doping ratios. Fourier transformed infrared spectroscopy also confirmed the standard ZnO profiles at lower doping ratios but additional phases at higher doping. Vibrating sample magnetometer showed soft ferromagnetic behavior for low impurity samples and harder ferromagnetic behavior for higher doping at room temperature. A simultaneous differential scanning calorimetry/thermo gravimetric analysis was performed to study the phase variations during crystallization.

Synthesis and structural, magnetic characterization of Zn(Mn)O diluted magnetic semiconductor

The bulk samples with nominal composition Zn1−x Mnx O [x=5% and 7%] were synthesized at 930°C by Standard Solid State Reaction method. The structural analysis reveals the single phase nature. The Topography study indicates the distribution of the particles. Magnetic property was affirmed by Vibrating Sample Magnetometer, Zn1−x Mnx O (with x=5%), low concentration of dopant shows good ferromagnetism compared to high concentration in Zn1−x Mnx O (with x=7%).

Synthesis of stable and highly luminescent beryllium and magnesium doped ZnS quantum dots suitable for design of photonic and sensor material

Highly luminescent ZnS quantum dots (QDs) and their Be2+ and Mg2+ derivatives having nominal compositions Zn1−xBexS and Zn1−xMgxS (where x=0.0–0.6 and Δx=0.1) have been synthesized using the co-precipitation technique. The synthesized QDs are stable for a period of up to 7 months. They have a cubic closed packed (zinc blende) structure and average particle size of 2–3nm as measured by TEM, XRD and UV–vis spectral analysis. Incorporation of Be2+ and Mg2+ into the ZnS lattice has shown noteworthy effects on the intensity of defect-states emission that enhances the luminescence intensity of the QDs. The absorption bands in the visible spectral range for ions of Be and Mg elements are observed to overlap with the fluorescence transitions of ZnS QDs. These highly luminescent and stable QDs could be utilized for the development of new quantum dot-based sensors, light emitting diodes, phosphor and coating for long term applications.

Influence of lithium doping on the structural and electrical characteristics of ZnO thin films

Thin films of undoped and lithium-doped Zinc oxide, (Zn1−xLix)O; x=0, 0.05, 0.10 and 0.20 were prepared by sol–gel method using spin-coating technique on silicon substrates [(111)Pt/Ti/SiO2/Si)]. The influence of lithium doping on the structural, electrical and microstructural characteristics have been investigated by means of X-ray diffraction, leakage current, piezoelectric measurements and scanning electron microscopy. The resistivity of the ZnO film is found to increase markedly with low levels (x≤0.05) of lithium doping thereby enhancing their piezoelectric applications. The transverse piezoelectric coefficient, e31⁎ has been determined for the thin films having the composition (Zn0.95Li0.05)O, to study their suitability for piezoelectric applications.

Ferromagnetic resonance in Ni–Zn ferrite nanoparticles in different aggregation states

Ferrite nanoparticles of composition Zn0.5Ni0.5Fe2O4 were synthesized by forced hydrolysis in polyol from the corresponding zinc, nickel and iron acetates. By varying the preparation conditions, different aggregation states were obtained, ranging from isolated nanoparticles with average diameter of 5nm, to clusters of some 20nm, formed as well by nanoparticles with average diameter in the 5nm range, as confirmed by X-ray diffraction and high resolution transmission electron microscopy. Ferromagnetic resonance measurements exhibited a ferrimagnetic behavior for both aggregation states at 77K; at 300K, however, isolated nanoparticles showed a superparamagnetic behavior while clustered ones remained ferrimagnetic with a broad linewidth. These results are interpreted on the basis of interactions between nanoparticles.

Li-substituted Mn-Zn ferrite: Structural and Magnetic Properties After Different Thermal Treatments

Spinel ferrites of composition Zn0.6Mn0.4Fe2O4 and Li0.2Zn0.2Mn0.4Fe2.5O4 were prepared by the self-combustion sol-gel method. The samples were heat-treated in different atmospheres and temperatures, producing different effects on their morphological and structural properties. The resulting products of each treatment were structurally and magnetically characterized. Incorporating Li to the crystalline lattice increases saturation magnetization and promotes a decrease in secondary phases’ segregation. This result is explained assuming that Li incorporation produces a cationic redistribution in the spinel structure.

Ferromagnetic resonance behavior of spark plasma sintered Ni–Zn ferrite nanoparticles produced by a chemical route

Ferrite nanoparticles of composition Zn0.5Ni0.5Fe2O4 were prepared by forced hydrolysis in a polyol (polyol process) from the corresponding iron, nickel, and zinc acetates. Synthesis conditions allowed for obtaining polycrystalline epitaxial clusters of about 22 nm in size with an average crystal size of about 5 nm. These powders were subsequently consolidated by spark plasma sintering (SPS) technique under a pressure of 80 MPa and temperatures in the 350 to 500 °C range for short periods (5 to 10 min). Densities reached 92% to 94% of the theoretical density. Particle size remained smaller than 61 nm, even for the highest temperature. Ferromagnetic resonance experiments at 77 K showed broadened resonance lines. In contrast with powdered nanoparticles, these high-density bodies can be used in many high-frequency applications.

Effect of doping with nickel ions on the structural state of a zinc oxide crystal

The fine structure of a hexagonal zinc oxide crystal doped with nickel ions of the composition Zn1 − xNixO has been studied using neutron diffraction and magnetic measurements. It is established that even at very low doping levels (x = 0.0004), the crystal undergoes local distortions in basal planes of the initial hexagonal lattice. The local distortions are assumed to be sources of the formation of ferromagnetism in compounds of this class.

Effect of Al and Sb doping on the magnetic properties of ZnMnO and ZnCoO

The bulk polycrystalline samples with nominal compositions Zn0.98−y(Mn∕Co)0.02(Al∕Sb)yO (y=0, 0.01, and 0.03) have been synthesized via solid state reaction route. The x-ray diffraction results reveal the presence of mainly wurtzite structure of pure ZnO in all the Al∕Sb codoped ZnMnO and ZnCoO samples. EDAX results confirm the presence of all elements in the samples in the stoichiometric ratio. While the Zn(Mn∕Co)O samples show paramagnetic behavior at room temperature, the Al∕Sb codoped ZnMnO samples exhibit room temperature ferromagnetism (RTFM) with saturation magnetization (Ms). The M-H curves of Al∕Sb codoped ZnCoO samples show almost linear variation with a small kink at the origin, indicating the presence of weak ferromagnetism in the Al∕Sb codoped ZnCoO samples. Possible mechanisms of the observed RTFM in Al∕Sb codoped Zn(Mn∕Co)O samples are discussed in this paper.