排序方式: 共有367条查询结果,搜索用时 187 毫秒
51.
A Simple Route of Morphology Control and Structural and Optical Properties of ZnO Grown by Metal-Organic Chemical Vapour Deposition
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Employing the metal-organic chemical vapour deposition (MOCVD) technique, we prepare ZnO samples with different morphologies from the film to nanorods through conveniently changing the bubbled diethylzinc flux (BDF) and the carrier gas flux of oxygen (OCGF). The scanning electron microscope images indicate that small BDF and OCGF induce two-dimensional growth while the large ones avail quasi-one-dimensional growth. X-ray diffraction (XRD) and Raman scattering analyses show that all of the morphology-dependent ZnO samples are of high crystal quality with a c-axis orientation. From the precise shifts of the 20 locations of ZnQ (002) face in the XRD patterns and the E2 (high) locations in the Raman spectra, we deduce that the compressive stress forms in the ZnO samples and is strengthened with the increasing BDF and OCGF. Photoluminescence spectroscopy results show all the samples have a sharp ultraviolet luminescent band without any defects-related emission. Upon the experiments a possible growth mechanism is proposed. 相似文献
52.
Polycrystalline samples with nominal composition of La0.7Ca0.3Mn1−xVxO3 (0?x?0.2) sintered in air were investigated by ac susceptibility, dc magnetization, magnetoresistance (MR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential thermal analysis (DTA) measurements. It is found that V could not substitute for Mn to form La0.7Ca0.3Mn1−xVxO3 phase when the samples are sintered in air. The obtained samples contain several phases such as (La, Ca)Mn1−δO3, LaCa3V3O12, Mn3O4 phases, etc. and constitute multi-phase composites. The Curie temperature TC and spontaneous magnetization of the composites decrease, and the resistance of the composites increases as the V content increases. The addition of V may effectively improve the low-field MR response at low temperatures due to the variation in the microstructure of the composites. 相似文献
53.
We study the deterministic spin dynamic of two interacting magnetic moments with anisotropy and dipolar interaction under the presence of an applied magnetic field, by using the Landau–Lifshitz equation with and without a damping term. Due to different kinds of interactions, different time scales appear: a long time scale associated with the dipolar interaction and a short time scale associated with the Zeeman interaction. We found that the total magnetization is not conserved; furthermore, for the non-dissipative case it is a fluctuating function of time, with a strong dependence on the strength of the dipolar term. In the dissipative case there is a transient time before the total magnetization reaches its constant value. We examine this critical time as a function of the distance between the magnetic moments and the phenomenological damping coefficient, and found that it strongly depends on these control parameters. 相似文献
54.
SmCoxTi0.4 (x=6.6, 7.1, 7.6, 8.1) ribbons have been prepared by melt spinning at a wheel speed of 42 m/s, followed by annealing at 750 °C for 2 h. Both as-spun and as-annealed ribbons possess the disordered TbCu7-type (1:7) phase even when the Sm/(Co,Ti) atomic ratio deviates from 1/7. The c/a ratio increases with increasing Co concentration x, but the unit cell volume decreases. The Curie temperatures show above 700 °C, increasing from 707 °C for x=6.6 to 782 °C for x=8.1. The saturation magnetizations increase almost linearly with increasing Co content. The observed magnetic hardening is believed to arise from the high magnetocrystalline anisotropy of the 1:7 phase and the fine nanograin structure. The intrinsic coercivity of 9797 Oe has been obtained in the melt-spun SmCo7.1Ti0.4 ribbons. 相似文献
55.
56.
Yunchen Du Sen LiuYanyan Ji Yonglai ZhangNi Xiao Feng-Shou Xiao 《Journal of magnetism and magnetic materials》2008
A series of highly ordered mesoporous materials (CF-SBA-15) with heat-resistant magnetism have been successfully prepared from impregnation of cobalt salt, iron salt, and citric acid with as-synthesized SBA-15. XRD and N2 isotherms indicate that these materials have highly ordered hexagonal mesoporous symmetry and open pore systems. The measurement of magnetic property shows that these materials are ferromagnetic even if calcined at 550 °C for 10 h in air, indicating their good heat-resistant magnetism. These results would be very important for recycle and regeneration of adsorbents and catalysts in practical applications. Moreover, this method may be useful for other mesoporous materials with thermally stable magnetism from a combination of other mesoporous materials such as MCM-41 with magnetic nanoparticles of MnFe2O4 and NiFe2O4. 相似文献
57.
58.
By using the Al'tshuler-Aronov-Spivak (AAS) model, we give the amplitude changing with Rashba spin-orbit interaction (SOI) and Dresselhaus SOI strength. In the first idea 1D square loop (SL), Rashba SOI acts on two sides while Dresselhaus SOI acts on the other two sides. In the second SL, we consume Rashba SOI and Dresselhaus SOI act on four sides simultaneously. This model can be replaced by another one that Rashba SOI and Dresselhaus SOI act on every side independently, and each side is twice long. We theoretically illustrate the influence of the Dresselhaus SOI on node position and number. To explain the “half oscillation” phenomenon found in experiment, we apply Dresselhaus SOI to the ideal 1D SL. The conclusion is that the Dresselhaus SOI has a strong effect on the emergence of “half oscillation”. 相似文献
59.
H. Gamari-Seale I.O. Troyanchuk K.L. Stefanopoulos 《Physica B: Condensed Matter》2008,403(17):2924-2929
In this paper we report the study of the perovskites La0.7Ca0.3Mn0.5Co0.5O3 and La0.8Sr0.2Mn0.5Co0.5O3 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 La0.7Ca0.3MnO3 and La0.8Sr0.2MnO3 destroys their long-range ferromagnetism exhibiting a cluster glass ferromagnetic order similar to the one observed in many cobaltites. 相似文献
60.
N. A. Tolstik G. Huber V. V. Maltsev N. I. Leonyuk N. V. Kuleshov 《Applied physics. B, Lasers and optics》2008,92(4):567-571
Polarized excited state absorption spectra of Er, Yb:YAB are reported. The Stark levels of the 4I15/2, 4I13/2, and 4I11/2 multiplets of Er3+ have been derived from the measured low-temperature absorption and fluorescence spectra. The stimulated emission spectra
have been calculated using the reciprocity method, and the radiative lifetime of the erbium 4I13/2 level has been determined indicating high nonradiative decay rates. The thermal conductivity of Er-Yb-codoped YAB crystals
has been measured. 相似文献