共查询到20条相似文献,搜索用时 15 毫秒
1.
Marina Koledintseva James Drewniak James Lenn 《Journal of magnetism and magnetic materials》2009,321(7):730-733
An analytical model for a magneto-dielectric composite material is presented based on the Maxwell Garnett rule for a dielectric mixture, and on Bruggeman's effective medium theory for permeability of a ferrite powder embedded in a dielectric. In order to simultaneously treat frequency-dispersive permittivity and permeability of a composite in a full-wave FDTD code, a new algorithm based on discretized auxiliary differential equations has been implemented. In this paper, numerical examples of modeling structures containing different magneto-dielectric mixtures are presented. 相似文献
2.
Grain size dependence of coercivity and permeability (GSDCP) theory is extended to include grain size distribution in ferromagnets. It is found that the experimental data do not agree with the GSDCP theory on the transition location of different grain size ranges (The GSDCP theory has three different grain size ranges for different magnetization processes.). Correspondingly, including the grain size distribution the GSDCP theory fits the experimental data very well. These results prove that the grain size distribution indeed affects the magnetic properties of nanocrystalline ferromagnets. 相似文献
3.
S. I. Lashkul V. N. Budnikov A. D. Gurchenko E. Z. Gusakov V. V. Dyachenko L. A. Esipov E. R. Its M. Yu. Kantor D. V. Kouprienko K. M. Novik A. Yu. Popov V. L. Selenin A. Yu. Stepanov V. B. Yermolajev S. V. Shatalin E. O. Vekshina 《Czechoslovak Journal of Physics》2002,52(10):1149-1159
Experiments at the FT-2 tokamak had demonstrated effective plasma LH heating, which was accounted for by both direct absorption
of RF power and plasma transport suppression. The improved core confinement accompanied by Internal Transport Barrier (ITB)
formation was observed. The RF pulse switch off is followed by triggering of LH transition and the External Transport Barrier
(ETB) formation near the last closed flux surface. The present paper is devoted to a much more detailed study of the radial
electric fieldE
r behaviour in the region of ITB and ETB and its influence on the tokamak microturbulence in these regions. The new experimental
data were obtained by spatial spectroscopic technique using additional pulse helium puffing in hydrogen plasma. Simultaneously
microscale plasma oscillations in the frequency band (0.01–2) MHz are observed with local enhanced microwave scattering diagnostics
and by x-mode fluctuation reflectometry. Experiments demonstrate that the improved confinement is associated with the modification
of microturbulence by the shear of theE×B poloidal velocity. This conclusion is also confirmed by the data obtained by Langmuir probes in the edge plasma.
Presented at 5th Workshop “Role of Electric Fields in Plasma Confinement and Exhaust”, Montreux, Switzerland, June 23–24,
2002”.
The study was performed with the support of the Ministry of General and Professional Education of RF (TOO-7.4-2797), INTAS-01-2056
and the RFBR Grants 00-02-16927, 01-02-17926 and 02-02-17684. 相似文献
4.
We studied the optical properties of mesoporous aluminosilica incorporated with metal nanoparticles, which can be used to efficiently enhance catalytic activity for CO oxidation. Analysis of the PL spectra indicated that the incorporation of Al greatly enhanced the generation of oxygen related defects. When Au nanoparticles were deposited onto Al-MCM-41, both the PL and PLE spectra suggested that the metal nanoparticles were strongly attracted by the electrostatic force induced by the charged oxygen defects. Electron spin resonance measurement provided further evidence, registering a spike in the intensity following incorporation of the metal particles, as the strong interaction between the F+ center and the metal particles induced electron transfer to the trapped O2 molecule. These discoveries shed further light on the perplexing mechanism by which the Si/Al ratio and metal particles can give rise to dramatic enhancement of the catalytic activity for CO oxidation. 相似文献
5.
R. Serna J. Gonzalo C.N. Afonso J.C.G. de Sande 《Applied physics. B, Lasers and optics》2001,73(4):339-343
Nanocomposite thin films formed by Cu nanocrystals (NCs) embedded in an amorphous aluminium oxide (Al2O3) host have been prepared by alternate pulsed laser deposition. Spectroscopic ellipsometry is used to determine the effective
refractive index (n=n+ik). The extinction coefficient is non-negligible and shows a broad absorption band related to the surface plasmon resonance.
In the neighbourhood of this wavelength, the real part of the refractive index undergoes an anomalous dispersion, leading
to a significant increase of the n value of the composite compared to that of the host. When the Cu content is low enough,
about 2 at. %, the use of an effective medium approach combined with a regression method allows us to determine the metal
content and film thickness from the ellipsometric measurements. For larger concentrations this approach is no longer valid.
Received: 31 July 2001 / Revised version: 21 September 2001 / Published online: 15 October 2001 相似文献
6.
Large third-order nonlinear optical susceptibility of Au-Al2O3 composite films near the resonant frequency 总被引:2,自引:0,他引:2
2 O3 composite films with high Au concentrations (30%–60% in volume fraction) were prepared by reactive co-sputtering and post
rapidly thermal annealing. The structure of the films and the size distributions of the Au nanoclusters were examined by TEM,
and the third-order nonlinear optical susceptibility χ(3) was measured by degenerated four-wave mixing using a 70-ps pulse laser at 532 nm. The maximum value of the χ(3) was about 1.2×10-6 esu in the annealed films and occurred at around 45% Au concentration. The figure of merit, χ(3)/α (α is the absorption coefficient), has a value of 7×10-12 esu cm over a wide range of Au concentrations.
Received: 23 July 1997 相似文献
7.
Christina H. Chen Ashil K. Higgins Reinhold M. Strnat 《Journal of magnetism and magnetic materials》2008
The effect of specimen geometry on magnetization distortion in closed-circuit measurements is reported in this letter. The degree of the distortion increases as the ratio of length to diameter (L/D) of specimen decreases, and the distortion can reduce the magnetization values as much as 42% when the applied magnetic field is 24 kOe and the L/D is 0.28. The type of magnetic material also affects the distortion. Although the phenomenon seems to be similar to the “image effect” that occurs in open-circuit measurements, reports of this effect in closed-circuit measurements have not been found in the literature. Further research effort, including 3D computer modeling, for understanding this magnetic phenomenon is underway and will be reported later. 相似文献
8.
Yakov M. Strelniker David J. Bergman 《Journal of magnetism and magnetic materials》2009,321(7):814-817
The strong-field magneto-transport in a generic three-dimensional composite with a periodic microstructure where all the constituents are normal metals is considered. The macroscopic response in such systems turns out to be considerably simpler than it is in the absence of a magnetic field. Closed form asymptotic expressions are found for the microscopic current distributions and macroscopic effective magneto-resistivity tensor components. Numerical calculations of the current distributions and effective magneto-resistivity tensor components are also performed and compared with the closed form asymptotic expressions. A new critical point is identified. 相似文献
9.
R.L. Smith 《Ultrasonics》1982,20(5):211-214
An expression has been derived for the effect of the grain size distribution in polycrystalline materials on the frequency dependence of the ultrasonic attenuation. It has been shown that two specimens with the same mean grain size can have significantly different ultrasonic attenuations if their grain size distributions are different and that no unique solution in terms of the grain size exists for a particular ultrasonic attenuation against frequency curve. Qualitative agreement has been found between the theory and some of the experimental data available. 相似文献
10.
Helical polyurethane@attapulgite (HPU@ATT) composites were prepared after the surface modification of the rod-like attapulgite (ATT). HPU@ATT composites based on S-1,1′-binaphthyl-2,2′-diol (S-BINOL) with different optical purity (O.P.) were characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The results indicate that the helical polyurethane has been successfully grafted onto the surfaces of the modified ATT without destroying the original crystalline structure of ATT. The rod-like nanoparticles were confirmed by transmission electron microscopy (TEM). Infrared emissivity values of HPU@ATT composites have been investigated, and the results indicate that the optical purity of monomer plays a very important role in the infrared emissivity for HPU@ATT owing to the effect of helical conformation and interchain hydrogen bonds. Along with the increased optical purity of S-BINOL, the infrared emissivity of HPU@ATT is reduced evidently. Infrared emissivity value of HPU@ATT based on S-BINOL with 100% optical purity is the lowest one (0.431). 相似文献
11.
B. Ya. Balagurov 《Technical Physics》2012,57(8):1051-1057
The influence of the shape of inclusions on the conductivity of composites, including critical concentration N c (percolation threshold), is considered using 2D models as an example. A relationship between constant N I , which characterizes effective conductivity ?? e for low concentrations N of inclusions and percolation threshold N c is established. 相似文献
12.
Bin Li Yan Liu Zhongwei Tan Huai Wei Yanhua Wang Wenhua Ren Shuisheng Jian 《Optics Communications》2008,281(6):1492-1499
A novel method of adjusting the dispersion of fiber Bragg grating is proposed using the non-uniform stress effect. By loading the axial stress on the fiber grating coated with non-uniform copper thin-film, the induced non-uniform stress effect can realize the tunable dispersion of grating. The non-uniform copper films are plated on the outer cladding of fiber grating and the thickness of the copper film gradually changes along the grating length. Numerical models are established to analyze the dynamic tunable characteristics of such grating when loading different axial stresses on it. The model is verified by experiments. 相似文献
13.
In the investigations of antiferromagnetic (AF)/ferromagnetic (FM) bilayer samples, often distinct experimental techniques yield different values for the measured exchange anisotropy field (HE). We propose that the observed discrepancy may be accounted in part by the dependence of the unidirectional anisotropy with the value of the externally applied cooling field (h). Using a simple microscopic model for representing the AF/FM interface, which incorporates the effect of interface roughness, we show that the interface energy between the AF and FM layer indeed varies with h, as recently observed in anisotropic magnetoresistance measurements, lending support to our proposal. 相似文献
14.
C.H. Chia C.T. Yuan S.L. Yang J.Y. Juang K.C. Chiu S.Y. Jeng 《Journal of luminescence》2008,128(1):123-128
A detailed photoluminescence investigation of the thermal redshift and broadening of the excitonic line of cubic CdSe film grown by molecular beam epitaxy is presented. Free excitonic emission from the cubic CdSe film was observed at low temperature. Temperature-dependent measurement was performed to obtain material parameters related to exciton-phonon interaction by fitting the experimental data to the phenomenological model. The relative contribution of both acoustic and optical phonon to the band gap shrinkage and exciton linewidth broadening are discussed. Exciton binding energy of 16±1.5 meV was determined from the Arrhenius analysis. 相似文献
15.
It is shown that the relations generally used for interpreting the frequency dependence of complex susceptibility caused by magnetic after-effect differ from those obtained by consistent application of the Néel theory. These more exact expressions are derived and it is shown that they represent the measured dependence better. 相似文献
16.
M. A. Ormont 《Moscow University Physics Bulletin》2011,66(2):162-168
The effect of electron state hybridization on phononless hopping conductivity in a disordered system of point localization
centers in the intermediate frequency range corresponding to electron transitions to distant centers is discussed. When the
basis of the atom-type localized functions is applied, with the hybridization of the wave functions of the distant centers
not being taken into account, the frequency dependence of phononless conductivity is shown to be superlinear and monotonic
in a wide frequency range. In this case, the kink in the vicinity of a crossover from a linear to a quadratic frequency dependence
of the conductivity turns out to be sharper as distinct from the standard theory. 相似文献
17.
We present study of the anisotropic magnetocaloric effect in DyNiAl. This compound crystallizes in the hexagonal ZrNiAl-type structure, orders magnetically below and undergoes a further magnetic phase transition at . The Dy-moments are aligned ferromagnetically along the hexagonal c-axis below TC, the additional antiferromagnetic component develops within the basal plane below T1. The magnetocaloric effect was evaluated from the magnetization measurements with field applied along the c-axis and perpendicular to it. Our data reveal a strong anisotropy of the magnetocaloric effect. The large effect occurs for field applied along the c-axis whereas the entropy change is small for the perpendicular field direction. 相似文献
18.
Influence of shape anisotropy on microwave complex permeability in carbonyl iron flakes/epoxy resin composites
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To explore the mechanism of carbonyl iron flake composites for microwave complex permeability, this paper investigates the feature of the flakes. The shape anisotropy was certified by the results of the magnetization hysteresis loops and the Mossbauer spectra. Furthermore, the shape anisotropy was used to explain the origin of composite microwave performance, and the calculated results agree with the experiment. It is believed that the shape anisotropy dominates microwave complex permeability, and the natural resonance plays main role in flake. 相似文献
19.
20.
A. Pérez-Junquera J.I. Martín J.V. Anguita G. Rodríguez-Rodríguez M. Vélez H. Rubio L.M. Alvarez-Prado J.M. Alameda 《Journal of magnetism and magnetic materials》2007
Diluted arrays of elliptical antidots have been fabricated by optical lithography, electron beam lithography and plasma etching on amorphous Co74Si26 magnetic films with a well-defined uniaxial anisotropy. The magnetic behavior of two identical antidot arrays but with different hole depth in comparison with film thickness has been studied by transverse magneto-optical Kerr effect. Significant differences appear in the coercivity depending on whether the magnetic film is completely perforated or not, indicating a much more effective domain wall pinning process when the depth of the holes is smaller than the magnetic film thickness. 相似文献