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1.
MnWO4 nano- and microcrystals with various morphologies have been prepared by the surfactant-assisted hydrothermal method. The crystals were characterized by X-ray diffraction, scanning electron microscopy and magnetic measurements. Different morphologies and growth mechanisms of MnWO4 crystals depend on the surfactant employed. Our results reveal that the MnWO4 nanocrystals exhibit weak ferromagnetism at low temperature due to incomplete spin compensation on the surface with nanoparticle size, while microflowers show antiferromagnetic behavior at low temperature. The crystal morphologies and the size effects associated with surfactants result in these tunable magnetic behaviors. 相似文献
2.
《Journal of magnetism and magnetic materials》1999,195(2):514-519
The spin configurations in the absence of an external magnetic field have been systematically investigated for a magnetic bilayer system consisting of two ferromagnetic layers separated by a non-magnetic layer with interlayer exchange coupling. Based on a phenomenological model, the conditions for the existence of collinear and non-collinear spin structures were derived for three kinds of magnetic bilayers with different combinations of in-plane cubic and uniaxial anisotropies for the two ferromagnetic layers. The phase diagrams of the spin configurations at zero field were drawn, taking into account the lowest-order anisotropy parameters of both the ferromagnetic layers. The values of the canting angle have been derived analytically and then numerically plotted. 相似文献
3.
V. I. Klyatskin O. G. Chkhetiani 《Journal of Experimental and Theoretical Physics》2009,109(2):345-356
We have derived an equation for the probability density of the magnetic energy in a random Gaussian, delta-correlated in time,
divergent velocity field in the absence of molecular diffusion effects. Basic statistical characteristics of the energy have
been calculated using this equation. Based on the ideas of statistical topography, we have studied the processes of magnetic
field amplification in space and, in particular, the conditions for the formation of a cluster structure. These phenomena
are coherent, occur with a probability equal to unity, and, hence, manifest themselves almost in all individual realizations
of the process. The clustering effect is demonstrated with an exact solution for the magnetic field dynamics for the simplest
model of a random divergent velocity field. 相似文献
4.
He Jiang Xiao Fang LiuZhi Yu Zou Zhang Ben WuBo He Rong Hai Yu 《Applied Surface Science》2011,258(1):236-241
A series of Co-doped SnO2 nanoparticles have been synthesized by the co-precipitation route. Different amounts of surfactant have been used in order to study the effect of surfactants (CTAB) on the magnetic and optical properties. Structural analyses reveal that Co dopants are substituted into rutile SnO2 nanoparticles without forming any secondary phase. The increase of the surfactant promotes the adsorption of organic molecules on the surfaces of nanoparticles. Meanwhile, both the ferromagnetism and the orange emission drop progressively. The dependence of ferromagnetic properties on the surfactant concentration could be explained based on the bound magnetic polaron, where the carriers are provided by oxygen vacancies. XANES spectra reveal that the electrons transfer from Co 3d bands to the surfactant ions. Such electron-transfer process suppresses the formation of oxygen vacancies and leads to the decline of the ferromagnetism and optical emission. 相似文献
5.
O. I. Gnezdilov Yu. F. Zuev O. S. Zueva K. S. Potarikina O. G. Us’yarov 《Applied magnetic resonance》2011,40(1):91-103
Self-diffusion of surfactants and counterions in premicellar and micellar solutions of sodium, lithium and cesium dodecyl
sulfates has been examined by nuclear magnetic resonance (NMR)-diffusometry. Self-diffusion of surfactants obeys as a whole
the well-known two-site exchange model in which surfactants diffuse as micelles and non-micellized molecules in monomer and
dimer forms. To explain self-diffusion of counterions, the model which takes into account their diffusive motion about the
surface of micelles is proposed. It is shown that this phenomenon contributes considerably to charge transfer in micellar
solutions. Estimation of surface diffusion of counterions about the micellar surface is made on the basis of experimental
results on self-diffusion of surfactants and counterions, the data obtained on critical micelle concentration and the degree
of counterion binding. 相似文献
6.
Sima Alikhanzadeh-Arani Masoud Salavati-Niasari Mohammad Almasi-Kashi 《Journal of magnetism and magnetic materials》2012
A new way of preparing FeCo nanoparticles has been developed using the co-precipitation technique based on the appropriate Co precursors of different types of ligands. These new precursors have been prepared by the reaction of cobalt acetate with three various coordination compositions for forming cobalt complex types. This technique provides proper control on nanoparticle size distribution after annealing to 500 °C. The variation of the magnetic properties with the type of ligands of Co can arise from the changes of the microstructures and crystalline anisotropies. Maximum coercivity values of 480 Oe were obtained. It is found that the precursors with special structures can prevent from agglomeration without presence of any surfactants. 相似文献
7.
Dopants and defects are important in semiconductor and magnetic devices. Strategies for controlling doping and defects have been the focus of semiconductor physics research during the past decades and remain critical even today. Co-doping is a promising strategy that can be used for effectively tuning the dopant populations, electronic properties, and magnetic properties. It can enhance the solubility of dopants and improve the stability of desired defects. During the past 20 years, significant experimental and theoretical efforts have been devoted to studying the characteristics of co-doping. In this article, we first review the historical development of co-doping. Then, we review a variety of research performed on co-doping, based on the compensating nature of co-dopants. Finally, we review the effects of contamination and surfactants that can explain the general mechanisms of co-doping. 相似文献
8.
LIU RongZheng ZHAO YuZhen HUANG RongXia ZHAO YongJie & ZHOU HePing State Key Laboratory of New Ceramics Fine Processing 《中国科学:物理学 力学 天文学(英文版)》2011,(7)
Iron oxide particles with various shapes,sizes and phase concentrations(including--Fe2O3 and Fe3O4) have been synthesized through a simple hydrothermal method in the ethylene glycol(EG)-water system.In the preparation conditions,ferric chloride(FeCl3.6H2O) was used as the iron source in the presence of sodium hydroxide(NaOH) without any surfactants.By adjusting the experimental parameters(EG/H2O ratio,base content,iron ions concentration,etc.),the shape,the size,the phase and the magnetic property of the pr... 相似文献
9.
The effects of the solvent-surfactant interaction, chain length and stiffness of surfactants on the formation of aggregates
and the aggregation degree of surfactants in the two-dimension solution have been investigated using discontinuous molecular-dynamics
simulations. When the tail-water repulsion increases or the head-water attraction decreases, the aggregation degree increases.
Increasing the chain length and raising the stiffness of surfactants lead to the increment of the aggregation degree.
Received 25 July 2001 and Received in final form 7 May 2002 相似文献
10.
The fluorescence and absorption spectra of Rose Bengal dye in aqueous solution have been studied in the presence of various nonionic, anionic and cationic surfactants. With cationic and nonionic surfactants, shifts occur in the absorption and emission peaks of the dye solution, with a large enhancement in the absorption and fluorescence intensity at the shifted λmax. No appreciable change in the absorption and fluorescence spectra of the dye has been observed on the addition of anionic surfactants.All the changes observed in the absorption and fluorescence spectra of the dye solution with surfactants may be attributed, to binding of the surfactant with dye molecules and the disaggregation of the dye multimer forms into the monomeric form. 相似文献
11.
12.
The effect of certain non-ionic, anionic and cationic surfactants on the fluorescence and absorption spectra of erythrosin has been studied. Shifts towards longer wavelengths in absorption and fluorescence peaks have been observed. Also, there appears to be a marked enhancement in the fluorescence intensity of erythrosin on adding small amounts of surfactants. The shift in the absorption peak wavelength appears to be due to the binding of the surfactant with dye molecules. The enhancement in the fluorescence intensity is attributed to the disaggregation of erythrosin dye dimer and multimer forms into the monomeric form. The change in the geometry of dye molecules in the presence of cationic surfactants has also been discussed. Enhancement in the fluorescence intensity on the addition of ethanol has been observed. 相似文献
13.
Ultra-thin Fe films have been grown on the sulphur passivated Ge(100) surface at 150°C. The growth, structure and the magnetic properties of the thin films were studied with LEED, AES, angle resolved AES and in-situ magneto-optical Kerr effect measurements. For the first five monolayers of Fe, no long-range order was observed . However, angle resolved AES data suggest that local order occurs with a small fraction of the Fe atoms adsorbed on bcc sites. For thicker Fe films, the growth becomes ordered. A comparison of the present study and with a previous study of the growth of Fe on sputter cleaned Ge(100)(2×1) surface, shows that sulphur passivation effectively prevents Fe–Ge intermixing. During the Fe deposition process, most of the sulphur atoms migrate to the growing surface, thus acting as surfactants. The presence of sulphur at the surface also affects the growth and magnetic properties of the thin films. 相似文献
14.
15.
Clustering analysis has been widely used to detect the functional connectivity from functional magnetic resonance imaging (fMRI) data. However, it has some limitations such as enormous computer memory requirement, and difficulty in estimating the number of clusters. In this study, in order to effectually resolve the deficiencies mentioned above, we have proposed a novel approach (SAAPC) for fMRI data analysis, which combines sparsity, an effective assumption for analyzing fMRI signal, with affinity propagation clustering (APC). 相似文献
16.
The dependence of Co nanoparticle sizes on the ratio of surfactants and the influence of different crystal sizes on magnetic properties 总被引:1,自引:0,他引:1
Y.K. Su C.M. Shen T.Z. Yang H.T. Yang H.J. Gao H.L. Li 《Applied Physics A: Materials Science & Processing》2005,81(3):569-572
Monodisperse cobalt nanoparticles were synthesized by high-temperature reduction of solution-phase cobalt chloride in the presence of a pair of surfactants, oleic acid and triphenylphosphine. Highly ordered two-dimensional superlattices of passivated cobalt nanoparticles were formed by a self-assembly technique. Analysis by X-ray diffraction, UV-vis absorption spectroscopy and transmission electron microscopy demonstrated that the size of the cobalt nanocrystals could be tuned by tailoring the concentration ratio of the two surfactants. In addition, the influence of different crystal sizes on magnetic properties of Co nanocrystals was also investigated. PACS 75.60.Nt; 75.50.Tt 相似文献
17.
Doina Bica Ladislau Vékás Mikhail V. Avdeev Oana Marinică Vlad Socoliuc Maria Bălăsoiu Vasil M. Garamus 《Journal of magnetism and magnetic materials》2007
Magnetic fluids (MFs), prepared by chemical co-precipitation followed by double layer steric and electrostatic (combined) stabilization of magnetite nanoparticles dispersed in water, are presented. Several combinations of surfactants with different chain lengths (lauric acid (LA), myristic acid (MA), oleic acid (OA) and dodecyl-benzene-sulphonic acid (DBS)) were used, such as LA+LA, MA+MA, LA+DBS, MA+DBS, OA+DBS, OA+OA and DBS+DBS. Static light scattering, transmission electron microscopy, small angle neutron scattering, magnetic and magneto-rheological measurements revealed that MFs with MA+MA or LA+LA biocompatible double layer covered magnetite nanoparticles are the most stable colloidal systems among the investigated samples, and thus suitable for biomedical applications. 相似文献
18.
氧化锌(ZnO) 纳米材料因其在UV 激光器、发光二极管、太阳能电池、稀磁半导体、生物荧光标示、靶向药物等领域中的广泛应用而成为最热门的研究课题之一. 调节和优化ZnO 纳米结构的性质是ZnO 的实际应用迫切所需. 在此, 通过发展聚乙烯吡咯烷酮导向结晶法、微波加热强制水解法、表面活性剂后处理法, 成功地制备出了尺寸、表面电荷或成分可调的球、半球、棒、管、T 型管、三脚架、片、齿轮、两层、多层、带盖罐子、碗等一系列ZnO 纳米结构. 通过简单地改变ZnO 纳米粒子的尺寸、形貌和表面电荷或成分, 有效地调控ZnO 本身的发光强度和位置, 并近90 倍地增强了荧光素染料的荧光强度; 诱使了强度可调的室温铁磁性; 实现了对ZnO纳米颗粒的细胞毒性的系统性调控. 相似文献
19.