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1.
We report on the analysis of optical transmittance spectra and the resulting ferromagnetic characteristics of sputtered Zn1−xCoxO films. Zn1−xCoxO films were prepared on (0001)-oriented Al2O3 substrates by the radio-frequency (rf) magnetron co-sputtering method. The XRD results showed that the crystallinity of films was properly maintained up to x=0.30 and no second phase peaks were detected up to x=0.40. The transmittance spectra showed both the increase of the absorption band intensity and the red shift of the absorption peak as well as the band edge with increasing x. We have proved experimentally that these changes depend on Co concentration. These optical properties suggest that sp-d exchange interactions and typical d-d transitions become activated with increasing x, which leads to the enhancement of ferromagnetic properties in Zn1−xCoxO films as shown in the AGM results. Therefore, it is concluded that the ferromagnetism derives from the substitution of Co2+ for Zn2+ without changing the wurtzite structure. 相似文献
2.
Chia-Lung Tsai Yow-Jon Lin Jia-Hong Chen Hsing-Cheng Chang Ya-Hui Chen Lance Horng Yu-Tai Shih 《Solid State Communications》2012,152(6):488-492
Zn0.8Co0.2O and Zn0.8Mn0.2O 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 Zn0.8Co0.2O and Zn0.8Mn0.2O films. It is found that ferromagnetic Zn0.8Mn0.2O has a higher Curie temperature than Zn0.8Co0.2O. In addition, the higher ratio of grain-boundary area to grain volume of Zn0.8Mn0.2O than Zn0.8Co0.2O indicates that grain boundaries and related acceptors are the intrinsic origin for ferromagnetism. 相似文献
3.
Ling Wei 《Applied Surface Science》2009,255(9):4992-4995
Zn1−xCoxO (0 ≤ x ≤ 0.15) thin films grown on Si (1 0 0) substrates were prepared by a sol-gel technique. The effects of Co doped on the structural, optical properties and surface chemical valence states of the Zn1−xCoxO (0 ≤ x ≤ 0.15) films were investigated by X-ray diffraction (XRD), ultraviolet-visible spectrometer and X-ray photoelectron spectroscopy (XPS). XRD results show that the Zn1−xCoxO films retained a hexagonal crystal structure of ZnO with better c-axis preferred orientation compared to the undoped ZnO films. The optical absorption spectra suggest that the optical band-gap of the Zn1−xCoxO thin films varied from 3.26 to 2.79 eV with increasing Co content from x = 0 to x = 0.15. XPS studies show the possible oxidation states of Co in Zn1−xCoxO (0 ≤ x ≤ 0.05), Zn0.90Co0.10O and Zn0.85Co0.15O are CoO, Co3O4 and Co2O3, with an increase of Co content, respectively. 相似文献
4.
L.F. Liu J.F. Kang Y. Wang H. Tang L.G. Kong X. Zhang R.Q. Han 《Solid State Communications》2006,139(6):263-267
CoxTi1−xO2−δ films have been prepared on Si(001) substrates by sol-gel method. When heat treated in air, CoxTi1−xO2−δ films are non-ferromagnetic at room temperature. However, after further vacuum annealing or hydrogenation, CoxTi1−xO2−δ films show room-temperature ferromagnetism (RTFM). When the vacuum annealed CoxTi1−xO2−δ films are reheated in air, the magnetic moments of the films strongly reduce. After these films are vacuum annealed once again, the magnetic moments are greatly enhanced, confirming the role of vacuum annealing in ferromagnetism of CoxTi1−xO2−δ films. The x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and measurements of magnetization (M) vs temperature (T) fail to detect Co clusters in the vacuum annealed and the hydrogenated CoxTi1−xO2−δ films. Oxygen vacancies are formed in CoxTi1−xO2−δ films after vacuum annealing and hydrogenation, determined by XRD and XPS measurements. These results indicate that oxygen vacancies created by vacuum annealing and hydrogenation play an important role in the generation of RTFM in CoxTi1−xO2−δ films. 相似文献
5.
Polycrystalline Zn1−xCoxO (x=0, 0.02, 0.05, 0.10 and 0.15) oxides have been synthesized by solid state reaction via sintering ZnO and Co powders in open air. X-ray diffraction analyses using Rietveld refinement indicate that a stoichiometric single phase with a wurtzite-like structure was found in Zn1−xCoxO samples with x up to 0.10. The elemental mapping using energy dispersive X-ray spectroscopic analyses presents a uniform distribution of Co. Optical transmittance measurements show that several extra absorption bands appear in the Co-doped ZnO, which is due to the transitions between the crystal-field-split 3d levels of tetrahedral Co2+ substituting Zn2+ ions. Raman measurements show that limited host lattice defects are induced by Co doping. Magnetization measurements reveal that the Co-doped ZnO samples are paramagnetic due to the absence of free carriers and in low temperature the dominant magnetic interaction is nearest-neighbor antiferromagnetic. 相似文献
6.
The electronic structures and magnetic properties of Zn1−xCoxO (x=5.55%,8.33%,12.5%) are studied using first-principles calculations in combination with Monte Carlo (MC) simulation. The combinational method makes possible a complete simulation from the microscopic magnetic interaction to macroscopic magnetic behavior. The calculated results from first principles indicate that the ferromagnetic ground state is stabilized by a half-metallic electronic structure which originates from the strong hybridization between Co 3d electrons and O 2p electrons. With the magnetic coupling strengths obtained from first-principles calculations, the MC simulation predicts the ferromagnetism of Zn1−xCoxO (x=5.55%,8.33%,12.5%) with , which is consistent with the experimental facts. 相似文献
7.
We report on the ferromagnetic characteristics of Zn1−xMnxO films (x=0.1-0.3) prepared by the sol-gel method on silicon substrates using transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD) and superconducting quantum interference device (SQUID) magnetometry at various temperatures. Magnetic measurement show that the Curie temperature (TC) and the coercive field (HC) were ∼39 K and ∼2100 Oe for the film of x=0.2, respectively. EDS and TEM measurements indicate that Mn content at the interface is significantly higher than that at the center of the Zn0.8Mn0.2O film showing the ratio, Zn:Mn:O≅1:12:15. This experimental evidence suggests that ferromagnetic precipitates containing manganese oxide may be responsible for the observed ferromagnetic behavior of the film. 相似文献
8.
A.M. Abdel Hakeem 《Journal of magnetism and magnetic materials》2010,322(6):709-714
In view of recent controversies on above room-temperature ferromagnetism (RTFM) in transition-metal-doped ZnO, the present paper aims to shed some light on the origin of ferromagnetism by investigating annealing effects on structure and magnetism for polycrystalline Zn1−xMnxO powder samples prepared by solid-state reaction method and annealed in air at different temperatures. Magnetic measurements indicate that the samples are ferromagnetic at room temperature (RTFM). Room temperature ferromagnetism has been observed in the sample annealed at a low temperature of 500 °C with a saturated magnetization (Ms) of 0.159 emu/g and a coercive force of 89 Oe. A reduction in RTFM is clearly observed in the sample annealed at 600 °C. Furthermore, the saturation magnetic moment decreases with an increase in grain size, suggesting that ferromagnetism is due to defects and/or oxygen vacancy confined to the surface of the grains. The experimental results indicate that the ferromagnetism observed in Zn1−xMnxO samples is intrinsic rather than associated with secondary phases. 相似文献
9.
Ah Reum Han Seong-Ju Hwang Yongnan Zhao Young-Uk Kwon 《Journal of magnetism and magnetic materials》2008
The local atomic arrangement and electronic structure of the Co-doped Zn1−xCoxO nanocrystal have been quantitatively examined along with its magnetic properties. According to our analysis using powder X-ray diffraction, electron microscopy, and Zn K-edge X-ray absorption spectroscopy (XAS), phase-pure wurzite-structured Zn1−xCoxO nanocrystals have been successfully synthesized via the molten-salt method. The Co K-edge XAS analysis clearly demonstrates that all the Co2+ ions are substituted for the tetrahedral Zn sites of the Wurzite structure with a coordination number of 3.9 and a bond distance of 1.97 Å, ruling out the presence of magnetic impurity phase and Co-metal cluster. Magnetization measurements reveal that the present Zn1−xCoxO sample does not show any ferromagnetic transition down to 2 K. In this regard, we can conclude that Co-doped zinc oxide is not ferromagnetic but the previously reported ferromagnetism in this phase would be an extrinsic property. 相似文献
10.
R. Ghosh 《Applied Surface Science》2009,255(16):7238-7242
MgxZn1−xO (x = 0.0-0.20) thin films have been deposited by sol-gel technique on glass substrates and the effect of growth ambient (air and oxygen) on the structural, and optical properties have been investigated. The films synthesized in both ambient have hexagonal wurtzite structure. The c-axis lattice constant decreases linearly with the Mg content (x) up to x = 0.05, and 0.10 respectively for air- and oxygen-treated films, above which up to x = 0.20, the values vary irregularly with x. The change in the optical band gap values and the ultraviolet (UV) peak positions of MgxZn1−xO films show the similar change with x. These results suggest that the formation of solid solution and thus the structural and optical properties of MgxZn1−xO thin films are affected by the growth ambient. 相似文献
11.
L.F. Liu J.F. KangY. Wang H. TangL.G. Kong L. SunX. Zhang R.Q. Han 《Journal of magnetism and magnetic materials》2007
Co-doped TiO2 (CoxTi1−xO2, 0.05?x?0.2) films have been prepared on Si (0 0 1) substrates by sol–gel method. When heat treated in air, CoxTi1−xO2 films are non-ferromagnetic at room temperature. However, after further annealed in a flowing hydrogen atmosphere, CoxTi1−xO2 films show room-temperature ferromagnetism (RTFM). Measurements of magnetization (M) vs. temperature (T), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) fail to detect Co clusters in the hydrogenated Co0.1Ti0.9O2 films, suggesting that RTFM in the hydrogenated Co0.1Ti0.9O2 films may be intrinsic. But, metal Co appears in the hydrogenated Co0.2Ti0.8O2 films, showing that RTFM in the hydrogenated Co0.2Ti0.8O2 films is as least partly due to metal Co. These results indicate that hydrogen annealing can produce room-temperature ferromagnetism in CoxTi1−xO2 films, but it should be carefully designed to avoid the formation of metal Co in the hydrogenated CoxTi1−xO2 films. 相似文献
12.
Ternary polycrystalline Zn1−xCdxO semiconductor films with cadmium content x ranging from 0 to 0.23 were obtained on quartz substrate by pulse laser deposited (PLD) technique. X-ray diffraction measurement revealed that all the films were single phase of wurtzite structure grown on c-axis orientation with its c-axis lattice constant increasing as the Cd content x increasing. Atomic force microscopy observation revealed that the grain size of Zn1−xCdxO films decreases continuously as the Cd content x increases. Both photoluminescence and optical measurements showed that the band gap decreases from 3.27 to 2.78 eV with increasing the Cd content x. The increase in Cd content x also leads to the broadening of the emission peak. The resistivity of Zn1−xCdxO films decreases evidently for higher values of Cd content x. The shift of PL emission to visible light as well as the decrease of resistivity makes the Zn1−xCdxO films potential candidate for optoelectronic device. 相似文献
13.
Sujeet Chaudhary Kanwal Preet Bhatti S.C. Kashyap 《Journal of magnetism and magnetic materials》2009,321(8):966-970
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 (Zn99.5In0.5)1−xCoxO 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 Zn090Co0.1O thin film (having no indium). 相似文献
14.
Characteristics of high sensitivity ethanol gas sensors based on nanostructured spinel Zn1−xCoxAl2O4
Nanocrystalline powders of Zn1−xCoxAl2O4 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) mixed oxides, with cubic spinel structure were successfully prepared by the ethylene glycol mediated citrate sol-gel method. The structure and crystal phase of the powders were characterized by X-ray diffraction (XRD) and microstructure by transmission electron microscopy (TEM). X-ray diffraction results showed that the samples were in single phase with the space group Fd-3m. TEM analysis showed that the powders with spherical shape were uniform in particle size of about 17-24 nm with mesoporous in nature. Further investigations were carried out by FT-IR. Thick films of as-prepared Zn1−xCoxAl2O4 powders were fabricated using screen-printing technique. The response of Zn1−xCoxAl2O4 based thick films towards different reducing gases (liquefied petroleum gas, hydrogen, hydrogen sulfide, ethanol gas and ammonia) was investigated. The sensor response largely depends on the composition, temperature and the test gas species. The Co (cobalt) content has a considerable influence on the gas-sensing properties of Zn1−xCoxAl2O4. Especially, Zn0.4Co0.6Al2O4 composition exhibited high response with better selectivity to 100 ppm C2H5OH gas at 150 °C. The instant response (∼7 s) and fast recovery (∼16 s) are the main features of this sensor. 相似文献
15.
Sasanka Deka 《Solid State Communications》2005,134(10):665-669
The electronic structure of polycrystalline ferromagnetic Zn1−xCoxO (0.05≤x≤0.15) and the oxidation state of Co in it, have been investigated. The Co-doped polycrystalline samples are synthesized by a combustion method and are ferromagnetic at room temperature. XPS and optical absorption studies show evidence for Co2+ ions in the tetrahedral symmetry, indicating substitution of Co2+ in the ZnO lattice. However, powder XRD and electron diffraction data show the presence of Co metal in the samples. This give evidence to the fact that some Co2+ ion are incorporated in the ZnO lattice which gives changes in the electronic structure whereas ferromagnetism comes from the Co metal impurities present in the samples. 相似文献
16.
S. Ghosh 《Journal of magnetism and magnetic materials》2010,322(14):1979-1984
Single-phase Zn1−xCoxO (0.02≤x≤0.08) dilute magnetic semiconductor is prepared by mechanical milling process. The shift of XRD peaks towards the higher angle and a redshift in the band gap compared to the undoped ZnO ensure the incorporation of Co2+ ions in the semiconductor host lattice. Pure ZnxCo1−xO phases show the paramagnetic behavior in the temperature range 80 K≤T≤300 K. The room temperature volume magnetic susceptibility (χv) estimated in case of Zn0.96Co0.04O is ∼10−5 emu/Oe cm3. The temperature dependence of susceptibility χv can be fitted well with Curie law confirming the paramagnetic interaction. The observed crystal-field splitting of 3d levels of Co2+ ions inside Zn1−xCoxO has been successfully interpreted using Curie law. 相似文献
17.
Al-doped ZnO powders were synthesized via solid reaction between Zn(OH)2 and Al(OH)3 and consolidated by spark plasma sintering (SPS) to fabricate fine-grained Zn1−xAlxO ceramics as a thermoelectric material. X-ray diffraction and spectrophotometer experiments revealed that Al doping into ZnO is enhanced by the present process, and consequently the SPS-processed Zn1−xAlxO samples show significantly improved electrical conductivity as compared with those prepared via mixing ZnO and Al2O3 oxide powders. Because of the combined effect of Al doping and grain refinement, the present Zn1−xAlxO ceramics show much lower thermal conductivity, which also results in an enhanced dimensionless figure of merit (ZT), than un-doped ZnO oxides prepared also by SPS. 相似文献
18.
(Ga1−xMnx)N thin films grown on GaN buffer layers by using molecular beam epitaxy were investigated with the goal of producing diluted magnetic semiconductors (DMSs) with band-edge exciton transitions for applications in optomagnetic devices. The magnetization curve as a function of the magnetic field at 5 K indicated that ferromagnetism existed in the (Ga1−xMnx)N thin films, and the magnetization curve as a function of the temperature showed that the ferromagnetic transition temperature of the (Ga1−xMnx)N thin film was above room temperature. Photoluminescence and photoluminescence excitation spectra showed that band-edge exciton transitions in (Ga1−xMnx)N thin films appeared. These results indicate that the (Ga1−xMnx)N DMSs with a magnetic single phase hold promise for potential applications in spin optoelectronic devices in the blue region of the spectrum. 相似文献
19.
Evgeny V. Rebrov Pengzhao Gao Tiny M.W.G.M. VerhoevenJaap C. Schouten Richard KleismitZafer Turgut Gregory Kozlowski 《Journal of magnetism and magnetic materials》2011,323(6):723-729
Nanocrystalline Co2xNi0.5−xZn0.5−xFe2O4 (x=0−0.5) thin films have been synthesized with various grain sizes by a sol-gel method on polycrystalline silicon substrates. The morphology as well as magnetic and microwave absorption properties of the films calcined at 1073 K were studied using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and vibrating sample magnetometry. All films were uniform without microcracks. The Co content in the Co-Ni-Zn films resulted in a grain size ranging from 15 to 32 nm while it ranged from 33 to 49 nm in the corresponding powders. Saturation and remnant magnetization increased with increase in grain size, while coercivity demonstrated a drop due to multidomain behavior of crystallites for a given value of x. Saturation magnetization increased and remnant magnetization had a maximum as a function of grain size independent of x. In turn, coercivity increased with x independent of grain size. Complex permittivity of the Co-Ni-Zn ferrite films was measured in the frequency range 2-15 GHz. The highest hysteretic heating rate in the temperature range 315-355 K was observed in CoFe2O4. The maximum absorption band shifted from 13 to 11 GHz as cobalt content increased from x=0.1 to 0.2. 相似文献
20.
The magnetic and transport properties of nanocrystalline ZnxFe3−xO4 with x=0.0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0, respectively, fabricated by the sol-gel method have been investigated. Large magnetoresistance (MR) was observed and found to be originated both from the tunneling of the spin-polarized electrons across the adjacent ferromagnetic grains and the scattering by the canted spins at the grain surface near the grain boundaries. It has been revealed that the MR for the ZnxFe3−xO4 samples (x=0, 0.5 and 1.0) increases with the temperature decreasing from room temperature until a maximum is reached at around 55 K. Then a sharp drop occurs with the further decrease in temperature, regarded as a spin (cluster) glass transition. For the samples studied, a biggest low field (0.5 T) MR value of about 20% for x=0 at 55 K has been obtained. The mechanism of the MR behavior of the materials was discussed. 相似文献