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1.
Structural, compositional, optical and magnetic properties have been studied for polycrystalline (ZnO)0.90(TMO)0.10 bulk samples, where TM (transition metal ions) = Mn, Fe, and Co. The quantitative Rietveld analysis showed relatively higher percentage of impurity (spinel and oxide) phases of about 33.76, 52.38 and 55.61% for Mn, Fe and Co doped ZnO samples, respectively. The de-convolution of XPS spectra indicated the presence of different phases. The appearance of shaking satellites in XPS spectra confirmed the presence of different valence states of dopant ions. The red shift in energy band gap, estimated from reflectance UV-vis spectroscopy, was observed for all TM doped bulk samples. For Mn doping, paramagnetic behavior was obtained while for Co and Fe, weak ferromagnetic behavior was observed at room temperature. 相似文献
2.
With varying rapid thermal annealing temperature, luminescent properties of Zn0.75Mg0.25S:Mn thin film deposited by RF-magnetron sputtering technique were investigated. Although all samples were deposited from identical source composition, it was found that a main peak wavelength of photoluminescence of Zn0.75Mg0.25S:Mn depended on RTA temperatures and it shifted toward shorter wavelength upon the increase of RTA temperature. The same dependence of wavelength on RTA temperature was also observed in cathodoluminescence as well as electroluminescence measurements. It is noticeable that Zn0.75Mg0.25S:Mn thin film phosphor in this study showed more reddish emission than those of the previous studies.It was revealed that changes of the luminescent properties were originated from structural changes in Zn0.75Mg0.25S:Mn thin film phosphor from cubic to hexagonal phases using X-ray pole figure mapping, and the growing up of hexagonal phase mainly caused cracks and porous morphology on the surface of thin films. It is suggested that the phase transition would be the origin of luminescent property changes with respect to rapid thermal annealing temperature. 相似文献
3.
Yanyan Wei Denglu Hou Shuang Qiao Congmian Zhen Guide Tang 《Physica B: Condensed Matter》2009,404(16):2486-2488
Zn0.95−xCo0.05CuxO 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. 相似文献
4.
This paper investigates the structural, compositional and magnetic properties of vanadium doped ZnO bulk samples prepared by solid state reaction technique. The Rietveld refinement analysis for XRD results of samples showed small change in lattice parameters for 3 and 5% vanadium doped ZnO samples indicating the substitution of Zn2+ ions by vanadium ions in ZnO lattice. Raman spectroscopy reveals the change in ZnO modes positions due to vanadium doping. The appearance of E1 and E2 modes showed that the wurtzite structure of ZnO is still maintained after doping of vanadium oxide. XPS analysis confirms the presence of the different elements and oxidation states of vanadium ions. M-H curves obtained from VSM showed weak ferromagnetism in the samples. The observation of ferromagnetic behavior indicates the formation of ZnVO phase with V2+ ion substitution in the ZnO lattice. XPS scans of the etched bulk samples confirmed the 2+ oxidation state of vanadium ions in our samples explaining the origin of ferromagnetism. 相似文献
5.
V.K. Sharma M. NajimA.K. Srivastava G.D. Varma 《Journal of magnetism and magnetic materials》2012,324(5):683-689
We report on the structural and magnetic properties of the nanocrystalline samples of Zn1−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. 相似文献
6.
Magnetic and electric properties of transition-metal doped wurtzite CdSe from first-principles calculations 下载免费PDF全文
The geometrical structures of Cd0.75TM0.25Se (TM
= Ti, V, Cr and Mn) are optimized, and then their electric and
magnetic properties are investigated by performing
first-principles calculations within the generalized gradient
approximation for the exchange--correlation function based on
density functional theory. Cd0.75TM0.25Se (TM = Ti and V)
are found to have high spin-polarization near 100% at the Fermi
level. Cd0.75TM0.25Se (TM = Cr and Mn) are half-metallic
ferromagnets whose spin-polarization at the Fermi level is
absolutely +100%. The supercell magnetic moments of
Cd0.75Cr0.25Se and Cd0.75Mn0.25Se are 4.00 and
5.00~μB, which arise mainly from Cr-ions and Mn-ions,
respectively. The half-metallicity of Cd0.75Cr0.25Se is
more stable than that of Cd0.75Mn0.25Se. The electronic
structures of Cr-ions and Mn-ions are Cr eg2↑
t2g2↑ and Mn eg2↑
t2g3↑, respectively. 相似文献
7.
In this work, we aim to examine the spin-polarized electronic band structures, the local densities of states as well as the magnetism of Zn1−xTMxSe (TM=Cr, Fe, Co and Ni) diluted magnetic semiconductors in the ferromagnetic (FM) and antiferromagnetic (AFM) phases, and with 25% of TM. The calculations are performed by the developed full-potential augmented plane wave plus local orbitals method within the spin density functional theory. As exchange-correlation potential we used the generalized gradient approximation (GGA) form. We treated the ferromagnetic and antiferromagnetic phases and we found that all compounds are stable in the ferromagnetic structure. Structural properties are computed after total energy minimization. Our results show that the cohesive energies of Zn0.75TM0.25Se are greater than that of zinc blende ZnSe. We discuss the electronic structures, total and partial densities of states, local moments and the p–d exchange splitting. Furthermore, we found that p–d hybridization reduces the local magnetic moment of TM and produces small local magnetic moments on the nonmagnetic Zn and Se sites. We found also that in the AFM phase the TM local magnetic moments are smaller than in the FM phase; this is due to the greater interaction of the TM d-up and d-down orbitals. 相似文献
8.
L.V. Bau N.V. Khiem L.V. Hong P. Nordblad 《Journal of magnetism and magnetic materials》2010,322(6):753-312
Studies on La0.7Sr0.3Co1−xMnxO3 (x=0-0.5) compounds evidence that the interaction between Mn and Co ions in this system is antiferromagnetic super-exchange and not ferromagnetic (FM) double-exchange (DE). As a result, antiferromagnetism and magnetic glassiness develop steadily with increasing Mn content and the system becomes a spin glass at x∼0.1. Analyses of high-field magnetization data indicate that the system consists of two major phases: a metallic FM phase which magnetically saturates in rather low field, and an insulating non-FM phase which has a linear dependence of magnetization on magnetic field. In the low doping regime, the fraction of the non-FM component expands with temperature at the expense of the FM phase and becomes maximal at TC. Ferromagnetism reappears in highly doped (x≥0.2) compounds due to the presence of DE interaction between the Mn ions. The small volume fraction of the FM phase derived from the M(H) data in high-field region supports the coexistence of insulating and FM behaviors in the highly doped samples. 相似文献
9.
S.A. Chambers D.A. Schwartz W.K. Liu K.R. Kittilstved D.R. Gamelin 《Applied Physics A: Materials Science & Processing》2007,88(1):1-5
We have used oxygen plasma assisted metal organic chemical vapor deposition along with wet chemical synthesis and spin coating
to prepare CoxZn1-xO and MnxZn1-xO epitaxial and nanoparticle films. Co(II) and Mn(II) substitute for Zn(II) in the wurtzite lattice in materials synthesized
by both methods. Room-temperature ferromagnetism in epitaxial Co:ZnO films can be reversibly activated by diffusing in Zn,
which occupies interstitial sites and makes the material n-type. O-capped Co:ZnO nanoparticles, which are paramagnetic as
grown, become ferromagnetic upon being spin coated in air at elevated temperature. Likewise, spin-coated N-capped Mn:ZnO nanoparticle
films also exhibit room-temperature ferromagnetism. However, the inverse systems, N-capped Co:ZnO and O-capped Mn:ZnO, are
entirely paramagnetic when spin coated into films in the same way. Analysis of optical absorption spectra reveals that the
resonances Co(I)↔Co(II)+e-
CB and Mn(III)↔Mn(II)+h+
VB are energetically favorable, consistent with strong hybridization of Co (Mn) with the conduction (valence) band of ZnO. In
contrast, the resonances Mn(I)↔Mn(II)+e-
CB and Co(III)↔Co(II)+h+
VB are not energetically favorable. These results strongly suggest that the observed ferromagnetism in Co:ZnO (Mn:ZnO) is mediated
by electrons (holes).
PACS 75.50.Pp 相似文献
10.
采用共沉淀方法制备了名义组分为Zn1-xMnxO(x=0.001,0.005,0.007,0.01)的Mn掺杂的ZnO基稀磁半导体材料,并研究了在大气气氛下经过不同温度退火后样品的结构和磁性的变化.结果表明:样品在600℃的大气条件下退火后, 仍为单一的六方纤锌矿结构的ZnO颗粒材料;当样品经过800℃退火后,Mn掺杂量为0.007,0.01的样品中除了ZnO纤锌矿结构外还观察到ZnMnO3第二相的存在.磁性测量表明,大气条件下600℃退火后的样品,呈现出室温铁磁性;而800℃退火后的样品,其室温铁磁性显著减弱,并表现为明显的顺磁性.结合对样品的光致发光谱的分析,认为合成样品的室温铁磁性是由于Mn离子对ZnO中的Zn离子的替代形成的.
关键词:
ZnO
掺杂
稀磁半导体
铁磁性 相似文献
11.
The effect of cobalt-doping on the magnetic, transport and magnetoresistance characteristics of La1-xSrxMnO3 was investigated. The results show that the magnetoelectric property of
rare-earth doped manganites is greatly affected by substitution of Co for Mn sites. The Curie temperature as well as the magnetic moment decreases with the increase of doping concentration, and the samples exhibit obvious characteristics of the spin glass state. Moreover, the magnetoresistance is evidently modulated by doping concentration,
and the relevant temperature dependence is also suppressed. In addition, low-temperature magnetoresistance is significantly
promoted as doping concentration increases, which renders a value of approximately 50% in the temperature range of 5--200~K and varies within 12.5%. It can be attributed to the effect of spin scattering, induced by cobalt doping, on the itinerant electrons of Mn ions, thus introducing a spin-disorder region into the ferromagnetic region of double-exchange interaction between neighbouring Mn3+ and Mn 3+ ions. 相似文献
12.
Zn1−xCdxO nanocrystalline powder with different Cd contents (0≤x≤1) has been prepared by new facile sol–gel route. The crystal structure and optical properties were investigated by X-ray diffraction patterns, Transmission electron microscope, X-ray photoelectron spectroscopy, Photoluminescence. As x varied from x=0 to 0.25, the Zn1−xCdxO nanopowder exhibits a hexagonal wurtzite structure of pure ZnO without any significant formation of a separated CdO phase. For the samples with 0.5≤x≤0.85, the Zn1−xCdxO nanopowder exhibits the coexistence of hexagonal ZnO and cubic CdO phase, meanwhile, the content of ZnO phase decreases while that of CdO increases with increasing the Cd content x. The ultra-violet near-band-edge emission of the Zn1−xCdxO nanopowder was monotonously red-shifted from 389 nm (x=0) to 406 nm (x=0.25) due to the direct modulation of band gap caused by Cd substitution. 相似文献
13.
We have studied the magnetic properties of Zn0.96M0.04O (M=Mn, Fe, Co) compounds prepared using several routes. The low temperature ceramic synthesis gave multiphasic samples and show ferromagnetic behavior. Single phases can be obtained by heating at higher temperatures (∼900–1100 °C). The use of very low oxygen pressure also favours the preparation of single-phases. We were also successful in preparing single-phase samples at very low temperature (∼400 °C) by using a sol-gel method. All of the samples without noticeable secondary phases in the X-ray patterns behave as conventional paramagnets. This is true even for the samples with very low grain size. Samples exhibiting secondary phases reveal spontaneous magnetization even at room temperature in some cases. Our results strongly support that ferromagnetism at room temperature is always due to the presence of secondary phases and not to the doping of ZnO. 相似文献
14.
Mn doped TiO2 nanoparticles are synthesized by sol–gel method. Incorporation of Mn shifts the diffraction peak of TiO2 to lower angle. The position and width of the Raman peak and photoluminescence intensity of the doped nanoparticles varies with oxygen vacancy and Mn doping level. The electron spin resonance spectra of the Mn doped TiO2 show peaks at g = 1.99 and 4.39, characteristic of Mn2+ state. Reduction in the emission intensity, on Mn doping, is owing to the increase of nonradiative oxygen vacancy centers. Mn doped TiO2, with 2% Mn, shows ferromagnetic ordering at low applied field. Paramagnetic contribution increases as Mn loading increases to 4% and 6%. Temperature dependent magnetic measurement shows a small kink in the ZFC curve at about 40 K, characteristic of Mn3O4. The ferromagnetic ordering is possibly due to the interaction of the neighboring Mn2+ ions via oxygen vacancy (F+ center). Increase in Mn concentration increases the fraction of Mn3O4 phase and thereby increases the paramagnetic ordering. 相似文献
15.
We carried out first-principles electronic structure calculation to study the structural stability and magnetic properties of Mn-doped WS2 ultra-thin films within the density functional theory. Adopting various configurations of Mn doping into WS2 bilayer, we find that the magnetic phase can be manipulated among the ferromagnetic, antiferromagnetic, or ferrimagnetic phases by altering doping level and growth environment. Magnetic phase and strength are determined by magnetic coupling of Mn dopants 3d electrons which can be attributed crucially to the exchange interaction mediated by neighboring S atoms 3p electrons. Accompanying to the magnetic phase transition, the electronic structure reveals that transport properties switch from semiconducting with various bandgap to half-metallic states. This result implicates possible way to develop magnetic semiconductors based on Mn doped 2D WS2 ultra-thin films for spintronics applications. 相似文献
16.
A. Samariya Sudhish Kumar S.C. Sharma D.C. Jain U.P. Deshpande E. Saitovitch 《Applied Surface Science》2010,257(2):585-590
Influence of Co doping for In in In2O3 matrix has been investigated to study the effect on magnetic vs. electronic properties. Rietveld refinement of X-ray diffraction patterns confirmed formation of single phase cubic bixbyite structure without any parasitic phase. Photoelectron spectroscopy and refinement results further revealed that dopant Co2+ ions are well incorporated at the In3+ sites in In2O3 lattice and also ruled out formation of cluster in the doped samples. Magnetization measurements infer that pure In2O3 is diamagnetic and turns to weak ferromagnetic upon Co doping. Hydrogenation further induces a huge ferromagnetism at 300 K that vanishes upon re-heating. Experimental findings confirm the induced ferromagnetism to be intrinsic, and the magnetic moments to be associated with the point defects (oxygen vacancies Vo) or bound magnetic polarons around the dopant ions. 相似文献
17.
We assumed that significant enlargement of the functional properties of the family of quaternary ZrCuSiAs-like pnictide-oxides, often called also 1111 phases, which are known now first of all as parent phases for new FeAs superconductors, may be achieved by replacement of non-magnetic ions by magnetic ions in semiconducting ZrCuSiAs-like phases. We checked this assumption by means of first-principles FLAPW–GGA calculations using a wide-band-gap semiconductor YZnAsO doped with Mn, Fe, and Co as an example. Our main finding is that substitution of Mn, Fe, and Co for Zn leads to drastic transformations of electronic and magnetic properties of the parent material: as distinct from the non-magnetic YZnAsO, the examined doped phases Y Zn0.89Mn0.11AsO, Y Zn0.89Fe0.11AsO, and Y Zn0.89Co0.11AsO behave as a magnetic semiconductor, a magnetic half-metal or as a magnetic gapless semi-metal, respectively. 相似文献
18.
采用基于密度泛函理论结合投影缀加平面波方法的VASP软件包,在考虑所有掺杂原子构型的前提下,对Cd掺杂ZnO合金的晶格常数、禁带宽度、电子态密度和形成焓进行了计算,分析了Cd含量和掺杂原子构型对纤锌矿wz-Zn1-xCdxO合金的电子结构和结构稳定性的影响.计算结果表明:随着Cd含量的不断增加,纤锌矿ZnCdO合金的平均晶格常数a,c均线性增加,但c/a的比值不会发生显著的变化;纤锌矿ZnCd
关键词:
密度泛函理论
ZnCdO合金
电子结构
形成焓 相似文献
19.
《Journal of Electrostatics》2014,72(3):181-186
Zinc doped LiCoPO4 was prepared by two step solid state reaction method. XRD studies ensure the formation of phase pure LiCoPO4 with olivine phase orthorhombic structure with pnma phase group. 2θ value of XRD peaks of LiCoPO4 is found to be shifted upon Zn2+ doping. The conductivity of pure LiCoPO4 is noticed to be increased by one order upon doping of Zn2+. The scaling behavior of Z″ indicates that the ion dynamical process are temperature independent for both pure and Zn2+ doped LiCoPO4. The temperature dependence of conductivity for both pure and Zn2+ doped sample obeys Arrhenius law of conduction. 相似文献
20.
Xingyan Xu 《Journal of magnetism and magnetic materials》2009,321(14):2216-2219
Single-phase Zn1−xCoxO (x=0.02, 0.04) powders were synthesized by a simple co-precipitation technique. X-ray diffraction analysis reveals that the Co-doped ZnO crystallizes in a wurtzite structure. The lattice constants of Co-doped ZnO powders decrease slightly when Co is doped into ZnO. Optical absorption spectra show a decrease in the bandgap with increasing Co content and also give an evidence of the presence of Co2+ ions in tetrahedral sites. Raman spectra indicate that Co doping increased the lattice defects and induced another Raman vibration mode around at 538 cm−1, which is an indicator for the incorporation of Co2+ ions into the ZnO host matrix. Magnetic measurement reveals that the Zn1−xCoxO (x=0.02, 0.04) powders clearly exhibit room-temperature ferromagnetic behavior, which makes them potentially useful as building components for spintronics. 相似文献