Properties of Cu and V co-doped ZnO nanoparticles annealed in different atmospheres

Zn_0.97Cu_0.01V_0.02O nanoparticles have been successfully prepared by the sol–gel method and sintered at 600 °C in argon and air atmosphere, respectively. The effects of annealing atmosphere on the structural, optical and magnetic properties of the obtained samples were studied. The X-ray diffraction result showed that the Zn_0.97Cu_0.01V_0.02O was single phase with the wurtzite structure of ZnO. The sample annealed in air had much better crystallization. Photoluminescence shows an increase in green emission when annealing in argon. The two Zn_0.97Cu_0.01V_0.02O samples exhibited ferromagnetism at room temperature. The ferromagnetism in this study was itself property of Cu, V co-doped ZnO and not originated from the secondary phase.     

Synthesis,structural, optical,and magnetic properties of Co doped,Sm doped and Co+Sm co-doped ZnS nanoparticles

The compositional, structural, optical and magnetic properties of ZnS, Zn_0.98Co_0.02S, Zn_0.98Sm_0.02S and Zn_0.96Co_0.02Sm_0.02S nanoparticles synthesized by a hydrothermal method are presented and discussed. X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) studies revealed that all the samples exhibited cubic structure without any impurity phases. X-ray photoelectron spectroscopy (XPS) results revealed that the Co and Sm ions existed in +2 and +3 states in these samples. The photoluminescence (PL) spectra of all the samples exhibited a broad emission in the visible region. The room temperature magnetization versus applied magnetic field (M–H) curves demonstrated that the Sm+Co doped nanoparticles exhibited enhanced ferromagnetic behavior compare to Co and Sm individually doped ZnS nanoparticles, which is probably due to the exchange interaction between conductive electrons with local spin polarized electrons on the Co²⁺ or Sm³⁺ ions. This study intensifies the understanding of the novel performances of co-doped ZnS nanoparticles and also provides possibilities to fabricate future spintronic devices.     

The magnetic mechanism of Zn<Subscript>0.93</Subscript>Co<Subscript>0.07</Subscript>O thin films

Zn_0.93Co_0.07O thin films infiltrated with nitrogen and aluminum were prepared by means of magneton sputtering. The structural and magnetic properties of the films were studied systematically. The materials were single phase (wurtzite structure) with surfaces showing signs of homogeneous growth. The films were ferromagnetic at room temperature, and magnetic domains could be clearly observed on the surfaces. In the case of Al infiltration, saturated magnetization increased with Al concentration increasing; whereas in the case of N infiltration, saturated magnetization decreased with the increase in N concentration. The results show that ferromagnetic interactions in Co-doped ZnO diluted magnetic semiconductor may be transferred by electrons. Supported by the National Natural Science Foundation of China (Grant No. 10674059) and the Major Project of National Basic Research Program of China (Grant No. 2005CB623605)     

Co掺杂对ZnO薄膜结构和性能的影响

采用PVA溶胶-凝胶方法，在玻璃衬底上制备了Zn_1-xCo_xO薄膜，利用X射线衍射仪(XRD)研究了不同Co含量对其微结构的影响.采用振动样品磁强计(VSM)测量了Zn_0.88Co_0.12O样品室温下的磁性.采用荧光光谱仪研究了Zn_1-xCo_xO样品室温下的发光特性，分析掺杂含量对其发光性能的影响，发现随着掺杂含量的增加，蓝光发光峰有一定的红移现象. 关键词： PVA方法 ZnO 掺杂     

Studies of the physical properties of Co, Cu codoped ZnO powders

Zn_0.95−xCo_0.05Cu_xO powders have been synthesized by the sol-gel method and the structural, magnetic and electrical properties of the powders have been investigated. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) indicate that the Co ions do not change the ZnO wurtzite structure. Magnetic measurements indicate that Co doping can induce room temperature (RT) ferromagnetism and the addition of Cu to the powders further increases the magnetic moment per Co ion. The effects of the introduction of Cu as an acceptor dopant in the host matrix are further studied using resistance measurements. It is demonstrated experimentally that acceptor doping plays an important role in realizing dominant ferromagnetic ordering in Co doped ZnO powders.     

Zn1-xCoxO稀磁半导体薄膜的结构及其磁性研究

利用X射线吸收精细结构、X射线衍射和磁性测量等技术研究脉冲激光气相沉积法制备的Zn_1-xCo_xO (x＝0.01,0.02)稀磁半导体薄膜的结构和磁性.磁性测量结果表明Zn₁-xCo_xO样品都具有室温铁磁性.X射线衍射结果显示其薄膜样品具有结晶良好的纤锌矿结构.荧光X射线吸收精细结构测试结果表明,脉冲激光气相沉积法制备的样品中的Co离子全部进入ZnO晶格中替代了部分Zn的格点位置,生成单一相的Zn_1-xCo_xO 稀磁半导体.通过对X射线吸收近边结构谱的分析,确定Zn_1-xCo_xO薄膜中存在O空位,表明Co离子与O空位的相互作用是诱导Zn_1-xCo_xO产生室温铁磁性的主要原因. 关键词： 1-xCo_xO稀磁半导体')" href="#">Zn_1-xCo_xO稀磁半导体 X射线吸收精细结构谱 脉冲激光气相沉积法     

Growth temperature dependent evolutions of microstructural, optical and magnetic properties of Zn0.75Co0.25O films

Zn0.75Co0.25O films are fabricated via reactive electron beam evaporation. The influence of growth temperature on the microstructural, optical and magnetic properties of Zn0.75Co0.25O films is investigated by using x-ray diffraction, selected area electron diffraction, field emission scanning electron microscope, high resolution transmitting electron microscope, photoluminescence （PL）, field dependent and temperature dependent DC magnetization, and x-ray photoelectron spectroscopy （XPS）. It is shown that Zn0.75Co0.25O films grown at low temperatures （250-350℃） are of single-phase wurtzite structure. Films synthesized at 300 or 350℃ reveal room temperature （RT） ferromagnetism （FM）, while su for 250℃ fabricated films is found above 56 K. PL and XPS investigations show favour towards the perspective that the O-vacancy induced spin-split impurity band mechanism is responsible for the formation of RT FM of Zn0.75Co0.25O film, while the superparamagnetism of 250℃ fabricated film is attributed to the small size effect of nanoparticles in Zn0.75Co0.25O film.     

On the origin of the ferromagnetism in Zn0.8Mn0.2O having a higher Curie temperature than Zn0.8Co0.2O

Zn_0.8Co_0.2O and Zn_0.8Mn_0.2O films were deposited on substrates by a sol–gel technique. X-ray diffraction, field-emission scanning electron microscopy, photoluminescence, and ferromagnetism measurements were used to characterize these dilute magnetic semiconductors. It is shown that the ferromagnetic properties might be related to the formation of acceptor-like defects in the Zn_0.8Co_0.2O and Zn_0.8Mn_0.2O films. It is found that ferromagnetic Zn_0.8Mn_0.2O has a higher Curie temperature than Zn_0.8Co_0.2O. In addition, the higher ratio of grain-boundary area to grain volume of Zn_0.8Mn_0.2O than Zn_0.8Co_0.2O indicates that grain boundaries and related acceptors are the intrinsic origin for ferromagnetism.     

High-temperature ferromagnetism in cobalt-doped ZnO single-crystalline nanorods

Co-doped ZnO single-crystalline nanorods with 80–100 nm in diameter and 1.5–2 μm in length have been prepared in a simple solution route. X-ray diffraction data and selected area electron diffraction pattern of the diluted magnetic semiconductor nanorods confirm the single crystallinity of Zn_1−xCo_xO solid solution without impurities of metallic Co or other phases. Magnetic results show that the Zn_0.95Co_0.05O nanorods exhibit a ferromagnetic characteristic with Curie temperature higher than 380 K. The high-temperature ferromagnetic properties allow this Zn_1−xCo_xO nanorods potential applications in future spintronic devices.     

Raman spectroscopy of Cu doping in Zn1−xCoxO diluted magnetic semiconductor

The room‐temperature ferromagnetism and the Raman spectroscopy of the Cu‐doped Zn_1−xCo_xO powders prepared by the sol–gel method are reported. The x‐ray diffraction (XRD) data confirmed that the wurtzite structure of ZnO is maintained for ZnO doped with Co below 10 at%. The magnetization–field curves measured at room temperature demonstrated that all Co‐doped ZnO powders were paramagnetic. Ferromagnetic ordering is observed for the samples doped with Cu in Zn_0.98Co_0.02O and strongly depends on the concentration of Cu. The relative strength of the second‐order LO peak to the first‐order one in the Raman spectra, which is related to the carrier concentration, of the Cu‐doped Zn_0.98Co_0.02O powder is strongly correlated with the saturation magnetic moment of the system. This seems to be in favor of the Ruderman‐Kittel‐Kasuya‐Yosida (RKKY) or double exchange mechanism of the ferromagnetism in this system. Copyright © 2009 John Wiley & Sons, Ltd.     

Ferromagnetism in diluted magnetic Zn-Co-doped CeO2−δ

Several oxides doped with transition metals can be used in spintronics devices due to their conductive and magnetic properties at room temperature. In this work, samples of Ce_1−2xZn_xCo_xO_2−δ were obtained by an alternative sol–gel proteic process for x=0.01, 0.05 and 0.1. The structural properties of samples were analyzed by XRD and Raman spectroscopy. Magnetization measurements revealed a ferromagnetic behavior at room temperature probably induced by oxygen vacancies.     

固相反应法制备Co掺杂ZnO的磁性和光学性能研究

研究了以固相反应法制备Co掺杂ZnO粉体的磁性和光学性能，测试结果表明对于均匀掺杂的Zn_0.95Co_0.05O粉体，Co²⁺随机取代Zn²⁺的位置进入ZnO晶格.Co²⁺之间的3d自旋电子耦合交换作用使得近邻的Co²⁺自旋反平行，Zn_0.95Co_0.05O粉体在3—300K表现为顺磁性，而非铁磁性. 关键词： ZnO 固相反应 稀磁半导体 顺磁性     

Structural and magnetic studies on transition metal (Mn, Co) doped ZnO nanoparticles

We report on the structural and magnetic properties of the nanocrystalline samples of Zn_1−x(TM)_xO (TM=Mn, Co and x=0.02, 0.05, 0.10) synthesized by chemical vapor deposition (CVD) method using different carrier gases i.e., Argon (Ar), Oxygen (O₂) and Nitrogen (N₂). X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies reveal wurtzite structure of pure ZnO in all the samples and particle sizes in the range of 15-40 nm. No evidence of any secondary phases having room temperature ferromagnetic behavior has been observed through XRD and TEM studies. Magnetic measurements reveal presence of mixed magnetic phases in the samples, which may be the reason for the low saturation magnetization in the nanoparticles.     

Enhanced ferromagnetic properties of diluted Fe doped ZnO with hydrogen treatment

The single-phase diluted magnetic Fe-ion (5%) doped ZnO powders were prepared by solid-state reaction method. The powders were annealed in Ar or Ar/H₂(5%) atmosphere at 1200 °C. The crystal structure, electric and magnetic properties for the Zn_0.95Fe_0.05O powders have been studied with X-ray diffraction (XRD) vibrating sample magnetometer, resistance and Hall measurement. All the peaks for the XRD pattern of samples belong to the hexagonal (P6₃mc) lattice of ZnO, and no indication of a secondary phase. The lattice parameters for the Zn_0.95Fe_0.05O with an annealing in Ar/H₂(5%) atmosphere were a₀=3.256 Å and c₀=5.206 Å at room temperature. The hysteresis curve for the Zn_0.95Fe_0.05O at room temperature was enhanced ferromagnetic behaviour with an annealing in Ar/H₂(5%) atmosphere. We give an explanation for enhanced ferromagnetic behaviour with H₂ treatment by electric properties.     

Synthesis and characterization of CoxZn1−xFe2O4 magnetic nanoparticles via a PEG-assisted route

We present an investigation of properties of Co_xZn_1−xFe₂O₄ (x=0.0-1.0) nanoparticles synthesized by a polyethylene glycol (PEG)-assisted hydrothermal route. X-ray powder diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and vibrating scanning magnetometry (VSM) were used to characterize the structural, morphological and magnetic properties. The particle size obtained from TEM and XRD are consistent with each other. It was observed that the lattice constant for each composition decreases with increasing Co substitution and follows Vegard's law. Magnetization measurements show that while the materials with high Zn substitution are superparamagnetic at room temperature, they are ferromagnetic at temperatures lower than the blocking temperature. The materials with less Zn substitution are ferromagnetic below room temperature. Magnetizations and the coercivities of the samples decrease with the Zn substitution. The resultant overall magnetic behavior of the superparamagnetic samples are found to be considerably different than that of conventional superparamagnetic systems due to the antiferromagnetic interactions both in intra- and inter-cluster spins, and size (effective moment) distribution of the particles.     

Structural and Magnetic Properties of Codoped ZnO based Diluted Magnetic Semiconductors

Zn1-xCoxO （x = 0.01, 0.02, 0.05, 0.10 and 0.20） diluted magnetic semiconductors are prepared by the sol-gel method. The structural and magnetic properties of the samples are studied using x-ray diffraction （XRD）, extended x-ray absorption fine structure （EXAFS） and superconducting quantum interference device （SQUID）. The XRD patterns does not show any signal of precipitates that are different from wurtzite type ZnO when Co content is lower than x = 0.10. An EXAFS technique for the Co K-edge has been employed to probe the local structures around Co atoms doped in ZnO powders by fluorescence mode. The simulation results for the first shell EXAFS signals indicate that Zn sites can be substituted by Co atoms when Co content is lower than x = 0.05. The SQUID results show that the samples （x 〈 0.05） exhibit clear hysteresis loops at 300K, and magnetization versus temperature from 5 K to 350K at H = 100 Oe for the sample x = 0.02 shows that the samples have ferromagnetism above room temperature. A double-exchange mechanism is proposed to explain the ferromagnetic properties of the samples.     

Study of point defect on the stability and magneto-optical properties of ZnO:Cu by first-principles

ABSTRACT

The magnetic and optical properties of Cu-doped ZnO systems have been widely studied in experimental, but the magnetic sources of the coexistence of Cu replacing Zn and the O vacancy systems are controversial. First-principles can compensate for the experimental deficiencies. The effects of Cu-doping and point defects on the magnetic and optical properties of ZnO were studied using geometry optimisation and energy calculation based on first-principle generalised gradient approximation?+?U method of the density functional theory. Results indicate that the band gaps and absorption spectra of Zn₁₅CuO₁₆, Zn₁₄CuO₁₆, and Zn₁₅Cu_iO₁₆ systems become narrowed and red-shifted, respectively, compared with those of pure ZnO. In addition, the system with Cu replaces Zn, and Zn vacancy coexists in ZnO. The doping system has the relatively largest magnetic moment and can achieve a ferromagnetic long-range order, and the Curie temperature can reach room temperature. As an electron injection source, this system can reach 100% electron spin-polarisation and exhibit half-metallic properties, which are relatively favourable for dilute magnetic semiconductor (DMS). Therefore, this system has certain theoretical reference value in the design and preparation of light-emitting devices or DMS.     

Co doped ZnO semiconductor materials: structural,morphological and magnetic properties

Structural, morphological and magnetic properties of Zn_1−xCo_xO (x = 0.01 and 0.03) powdered materials are presented. XRD studies reveal a wurtzite-type structure, while the formation of a Co₃O₄ secondary phase was evidenced by Raman spectroscopy. A ferromagnetic behaviour with low Curie temperature was evidenced by Electron Paramagnetic Resonance (EPR) investigation. We suggest that the origin of the ferromagnetism in Zn_1−xCo_xO powders is probably due to the presence of the mixed cation valence of Co ions via a double-exchange mechanism rather than the real doping effect.     

Effect of indium incorporation in Zn1−xCoxO thin films

In the present paper, the preliminary investigations of a series of ZnO thin films co-doped with indium and cobalt with an objective to elucidate the correlation, if any, between the carrier concentration and the induced room temperature ferromagnetism (RTFM), are presented. The single-phasic (Zn_99.5In_0.5)_1−xCo_xO thin films are deposited by spray pyrolysis. The substitution of Zn²⁺ by Co²⁺ has been established by optical transmission analysis of these films. The films are ferromagnetic at room temperature; and the magnetization has higher value for indium and cobalt co-doped thin film as compared with Zn0₉₀Co_0.1O thin film (having no indium).     

Magnetic and optical properties of Zn1– x Fe x O ( x = 0.05 and 0.10) diluted magnetic semiconducting nanoparticles

We have investigated the magnetic and optical properties of chemically low temperature-synthesized Zn_{1– x} Fe _x O (x = 0.05 and 0.10) diluted magnetic semiconducting nanoparticles (～7 nm). Observed magnetic behaviour of x = 0.05 samples showed that the net magnetic interaction was antiferromagnetic-like, a feature established by Curie–Weiss fit, concave Arrott–Belov–Kouvel (ABK) plots with the absence of spontaneous magnetization even at 5 K and stretched exponential-type time-dependent magnetization behaviour. Optimization of the Fe(x) dopant concentration in Zn_{1– x} Fe _x O gave the most favourable room-temperature ferromagnetism for x = 0.10, as supported by finite coercive field (～94.4 Oe) and remanent magnetization (0.011 µ_B/Fe ion) from strong hysteretic magnetization vs. magnetic-field curves at room temperature. The Curie temperature of the x = 0.10 sample was estimated at ～388 K. The existence of a room-temperature ferromagnetic phase was further established by the convex nature of the ABK plots with finite spontaneous magnetization. The observed magnetic behaviour for different x values is best explained by a magnetic polaron model.