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1.
Co 0.2Al xZn 0.8−xO films prepared with different molar ratio of aluminum nitrate to zinc acetate were deposited on substrates by the sol-gel technique. X-ray diffraction, photoluminescence and ferromagnetism measurements were used to characterize the Co 0.2Al xZn 0.8−xO diluted magnetic semiconductors. The authors found that the intensity of the acceptor-related photoluminescence increased with increasing aluminum concentration and an increase in the number of the acceptor-like defects (zinc vacancies especially) in the Co 0.2Al xZn 0.8−xO film might lead to the enhancement of the magnetic properties. This implies that controls of the aluminum concentration and the number of the acceptor-like defects are important factors to produce strong ferromagnetism Co 0.2Al xZn 0.8−xO films prepared by the sol-gel method. 相似文献
2.
Based on first-principles spin-density functional calculations, using the Korringa–Kohn–Rostoker method (KKR) combined with the coherent potential approximation (CPA), we investigated the magnetic and half-metallic properties of Mn-doped p-type ZnO and the mechanism which control these properties. Mn-doped ZnO is anti-ferromagnetic spin-glass state, but it becomes half-metallic ferromagnetic upon holes doping. The electronic structure, total magnetic moment of Zn 0.8Mn 0.2O 1−yN y and magnetic moments of Mn and N in Zn 0.8Mn 0.2O 1−yN y are calculated for different holes ( y) concentrations. In this paper we address the origin of half-metallic and ferromagnetic properties as controlled and oriented by the nature of hybridization of the Mn (3d) state and host p(N) states. The band structure has been used to explain the strong ferromagnetism observed in Zn 0.8Mn 0.2O 0.1N 0.9. 相似文献
3.
The effect of optical pumping and applied magnetic field on the characteristics of ferromagnetic layers in one-dimensional superlattices is studied. At low enough temperatures, these layers correspond to phase separation domains in RMn2O5 and R0.8Ce0.2Mn2O5 multiferroics. The formation of such domains occurs owing to the charge ordering of Mn3+ and Mn4+ ions and to the finite probability for eg electrons to tunnel between these pairs of ions. The volume occupied by such superlattices is rather small, and they can be treated as isolated ferromagnetic semiconductor heterostructures, spontaneously formed in the host crystal. The sequences of ferromagnetic resonances related to the superlattice layers in Eu0.8Ce0.2Mn2O5 are studied. The characteristics of these resonances give information on the properties of such layers. For the first time, it is demonstrated that the optical pumping gives rise to a new metastable state of superlattices, which can be recovered by the magnetic field cycling to the state existing before the optical pumping. It is found that the superlattices recovered by the magnetic field exist up to temperatures higher than those in as-grown crystals. 相似文献
4.
In this paper we report the study of the perovskites La 0.7Ca 0.3Mn 0.5Co 0.5O 3 and La 0.8Sr 0.2Mn 0.5Co 0.5O 3 by neutron powder diffraction at various temperatures and magnetization measurements in zero applied field and at low cooling regimes. The replacement of half Mn by Co in La 0.7Ca 0.3MnO 3 and La 0.8Sr 0.2MnO 3 destroys their long-range ferromagnetism exhibiting a cluster glass ferromagnetic order similar to the one observed in many cobaltites. 相似文献
5.
The pyroelectric response is measured using the dynamic method in preliminarily polarized magnetoelectric 0.8PbZr 0.53Ti 0.47O 3-0.2Mn 0.4Zn 0.6Fe 2O 4(0.8 PZT-0.2 MZF) and 0.8PbZr 0.53Ti 0.47O 3-Ni 0.4Zn 0.6Fe 2O 4 (0.8 PZT-0.2 NZF) composites, where PZT is a ferroelectric, and MZF and NZF are manganese-zinc and nickel-zinc ferrites,
respectively. Values of the pyroelectric coefficient Γ for the materials under study vary over the range of 1.5–4 × 10 −8 C cm −2 K −1. It is shown that the polarized samples of the composites have a heterogeneous distribution of polarization across the sample
thickness. The heterogeneity is more pronounced in the near-surface layers of the investigated materials. 相似文献
6.
Highly (0 0 2)-oriented Zn 0.8Cd 0.2O crystal films were prepared on different substrates, namely, glass, Si(1 1 1) and α-Al 2O 3(0 0 1) wafers by the dc reactive magnetron sputtering technique. The Zn 0.8Cd 0.2O/α-Al 2O 3 film has the best crystal quality with a FWHM of (0 0 2) peak of 0.3700°, an average grain size of about 200 nm and a root-mean-square surface roughness of about 70 nm; yet the Zn 0.8Cd 0.2O/glass holds the worst crystal quality with a much larger FWHM of 0.6281°. SIMS depth profile shows that the Zn and O compositions change little along the film depth direction; the Cd incorporation also almost holds the line towards the top surface other than an accumulation at the interface between the film and the substrate. The Cd content in the film is nearly consistent with that in target. 相似文献
7.
Zn1-xMnxO (x = O.Olq3.1) thin films with a Curie temperature above 300K are deposited on Al2O3 (0001) substrates by pulsed laser deposition. X-ray diffraction (XRD), ultraviolet (UV)-visible transmission and Raman spectroscopy are employed to characterize the microstructural properties of these films. Room temperature ferromagnetism is observed by superconducting quantum interference device (SQUID). The results indicate that Mn doping introduces the incorporation of Mn^2+ ions into the ZnO host matrix and the insertion of Mn^2+ ions increases the lattice defects, which is correlated with the ferromagnetism of the obtained films. The doping concentration is also proven to be a crucial factor for obtaining highly ferromagnetic Zn1-xMnxO films. 相似文献
8.
Room temperature ferromagnetic and paramagnetic Zn 0.98Mn 0.02O samples have been synthesized by the solid state reaction method and by selecting the final annealing temperature. Employing positron annihilation techniques, defects for both samples have been characterized. The results indicate that the presence of cation vacancy type defects is relatively less in the ferromagnetic Zn 0.98Mn 0.02O sample than in the paramagnetic Zn 0.98Mn 0.02O sample. 相似文献
9.
This paper reports that Zn 0.97Mn 0.03O thin films
have been prepared by radio-frequency sputtering technology followed
by rapid thermal processing in nitrogen and oxygen ambient
respectively. Magnetic property investigation indicates that the
films are ferromagnetic and that the Curie temperature (T c) is over
room temperature. It is observed that the saturation magnetization
of the films increases after annealing in nitrogen ambience but
decreases after annealing in oxygen. Room temperature
photoluminescence spectra indicate that the amount of defects in the
films differs after annealing in the different ambiences. This
suggests that the ferromagnetism in Zn 0.97Mn 0.03O films is
strongly related to the defects in the films. 相似文献
10.
Ferromagnetic insulator Pr 0.8Ca 0.2Mn 1–yCo y O 3 (0 ≤ y ≤ 0.7) thin films were epitaxially grown by pulsed laser deposition on substrates of (LaAlO 3) 0.3(SrAl 0.5Ta 0.5O 3) 0.7 (100). To probe the ferromagnetic insulator state, the Co content dependences of the structural, magnetic, and transport properties were studied. Variation of lattice constant by the Co substitution is well reproduced considering that divalent and trivalent Co ions substitute for Mn ions at the perovskite B‐sites. For 0 ≤ y ≤ 0.3, the Curie temperature, saturation magnetization, and magnetoresistance increase with increasing Co content, retaining the insulating properties. Detailed analyses of transport and magnetic properties indicate the contribution of both double exchange and superexchange interactions to the appearance of the ferromagnetic insulating phase. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
11.
以NH 3为掺N源,采用电子束反应蒸发技术生长了Mn和N共掺杂的Zn 1-xMn xO:N薄膜,生长温度为300℃,然后在O 2气氛中400℃退火0.5 h.X射线衍射测量表明,Zn 0.88Mn 0.12O(Mn掺杂)薄膜或Zn 0.88Mn 0.12O:N(Mn和N共掺杂)薄膜仍具有单一晶相纤锌矿结构,未检测到杂质相
关键词:
ZnO薄膜
Mn和N共掺杂
电学特性
磁特性 相似文献
12.
使用对Zn 2N 3:Mn薄膜热氧化的方法成功制备了高含N量的Mn和N共掺ZnO的稀磁半导体薄膜.在没有N离子共掺的情况下,ZnO:Mn薄膜的铁磁性非常微弱;如果进行N离子的共掺杂,就会发现ZnO:Mn薄膜在室温下表现出非常明显的铁磁性,饱和离子磁矩为0.23 μ B—0.61 μB.这说明N的共掺激发了ZnO:Mn薄膜中的室温铁磁性,也就是受主的共掺引起的空穴有利于ZnO中二价Mn离子的铁磁性耦合,这和最近的相关理论研究符合很好.
关键词:
磁性半导体
受主掺杂
空穴媒介的铁磁性 相似文献
13.
LiCr yNi 0.8−yCo 0.2O 2 compositions, where y=0.000, 0.010, 0.025, 0.040, 0.050, 0.075 and 0.100, were synthesized via a conventional ceramic route.
X-ray diffraction studies indicated cation mixing for the compositions with y ≥ 0.05. Cyclic voltammetric studies revealed
that the systems were reversible only when y was lower than 0.05. High levels of substitutions with Cr resulted in highly
irreversible systems, either due to cation mixing or the displacement of the substituent ions to the lithium inter-slab regions,
or both. The charge-discharge characteristics of LiCr yNi 0.8−yCo 0.2O 2 were similar to those of the unsubstituted material over ten cycles. All the other substituted compositions showed much lower
capacities and reduced cyclability. LiCr 0.025Ni 0.775Co 0.2O 2 gave a first-cycle capacity of 169 mAh/g in the 3.0 to 4.4 V window at a 0.1 C rate, fading to 156 mAh/g in the tenth cycle.
Differential scanning calorimetric studies revealed that substituting with chromium produced no benefit to thermal stability.
The structural, thermal and electrochemical properties of the pristine and Cr-substituted LiNi 0.8Co 0.2O 2 compositions are discussed. 相似文献
14.
从实验和理论上阐述了氧空位对Co掺杂ZnO半导体磁性能的影响.采用磁控溅射法在不同的氧分压下制备了Zn 095Co 005O薄膜,研究了氧分压对薄膜磁性能的影响.实验结果表明,高真空条件下制备的Zn 095Co 005O薄膜具有室温铁磁性,提高氧分压后制备的薄膜铁磁性逐渐消失.第一性原理计算表明,在Co掺杂ZnO体系中引入氧空位有利于降低铁磁态的能量,铁磁态的稳定性与氧空位和Co之间的距离密切相关.
关键词:
Co掺杂ZnO
稀磁半导体
第一性原理计算
氧空位缺陷 相似文献
15.
LiNi 0.8Co 0.2O 2 and Ca-doped LiNi 0.8Co 0.2O 2 cathode materials were synthesized via a rheological phase reaction method. It is found that the Ca doping significantly improves reversible capacity, cycling performance, thermal stability and rate capability. The Ca-doped LiNi 0.8Co 0.2O 2 cathode material maintains nearly its initial discharge capacity up to 100 cycles at room temperature. It also delivers an initial discharge capacity of 183 mA h g − 1 and still keeps 131 mA h g − 1 even after 120 cycles at 60 °C. These results, together with the X-ray diffraction and electrochemical impedance spectroscopy analysis, reveal that Ca 2+ ions occupy Li + ion sites to form Ca Li defects and lithium vacancies ( VLi′), which reduce the resistance and increases conductivity of LiNi 0.8Co 0.2O 2. 相似文献
16.
We report the fabrication of p-ZnO/n- Zn 0.8Cd 0.2O/n-ZnO heterojunctions that contain Al–N codoped p-ZnO, undoped n- Zn 0.8Cd 0.2O, and Al-doped n-ZnO layers. An InZn alloy is used as the p- and n-ZnO Ohmic contact electrodes. This structure exhibits improved rectifying p–n junction behavior, with forward turn-on voltage in the range of 3–5 V. The reverse breakdown voltage can be as high as 15 V, with 10 ?6-A reverse leakage current. Photoluminescence spectra show strong near band-edge emissions for both p- and n-ZnO at 368 nm and for undoped n- Zn 0.8Cd 0.2O, which is substantially red-shifted to 399 nm. 相似文献
17.
High temperature X-ray diffraction (HT-XRD), temperature programmed desorption (TPD), thermogravimetric analysis–differential thermal analysis (TGA/DTA) and neutron diffraction were combined to determine the structure and oxygen stoichiometry of SrCo 0.8Fe 0.2O 3−δ (SCF) and Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3−δ (BSCF) up to 1273 K in the pO 2 range of 1 to 10 − 5 atm. Formation of the vacancy-ordered brownmillerite phase, SrCo 0.8Fe 0.2O 2.5, was observed as a region of zero oxygen release in the TPD measurements and confirmed by HT-XRD and TGA/DTA. No ordering was observed in the BSCF system by any of the techniques utilized in this work. The oxygen vacancy concentration of BSCF was found to be considerably higher than that of SCF and always higher than that of the ordered brownmillerite phase of SCF, δ = 0.5. The combination of a high vacancy concentration and absence of ordering leads to higher oxygen permeation fluxes through BSCF membranes in comparison to SCF. 相似文献
18.
We report on the analysis of optical transmittance spectra and the resulting ferromagnetic characteristics of sputtered Zn 1−xCo xO films. Zn 1−xCo xO films were prepared on (0001)-oriented Al 2O 3 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 Zn 1−xCo xO films as shown in the AGM results. Therefore, it is concluded that the ferromagnetism derives from the substitution of Co 2+ for Zn 2+ without changing the wurtzite structure. 相似文献
19.
We report on the ferromagnetic characteristics of Zn 1−xMn xO 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 Zn 0.8Mn 0.2O 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
20.
La 1−xSr xMeO 3 (Me = Mn, Co, Fe) perovskites are used as cathodes and are also attractive materials for application as the contact layer between cathode and interconnect in solid oxide fuel cells. In this contribution, three perovskite series, La 0.8Sr 0.2Mn 1−xCo xO 3-δ (series 1), La 0.8Sr 0.2Fe 1−xCo xO 3-δ (series 2) and La 0.8Sr 0.2Mn 1−x/2Fe (1−x)/2Co xO 3-δ (series 3) with x = 0, 0.25, 0.5, 0.75 and 1 were re-investigated under identical synthesis and measurement conditions with the aim of obtaining a full overview of the quasi-ternary system La 0.8Sr 0.2MnO 3-δ–La 0.8Sr 0.2FeO 3-δ–La 0.8Sr 0.2CoO 3-δ. The distribution of the different crystallographic phases in the selected series, the DC electrical conductivity and the thermal expansion coefficients are presented. 相似文献
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