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141.
The Ising model with competing interactions is studied in a mean field effective medium approach. The phase diagram of such
model alloys is studied. We conclude that for all ratios of the competing interaction moments, a spin glass phase always exists
at low temperatures for certain concentration regimes. 相似文献
142.
The establishment of atomic short-range order (SRO) has been investigated in CuMn alloys (5, 8,13,16,20 at. % Mn) by measurement of the electrical resistivity during isochronal and isothermal annealing. An increasing degree of SRO is accompanied by a reduction of resistivity; this effect increases with Mn concentration. For 8,13 and 16 at. % Mn SRO kinetics turn out to deviate significantly from single exponential behavior with a maximum at 13 at. % Mn, whereas at 5 and 20 at. % Mn SRO is adjusted in a single exponential process. For data analysis three methods are used: a sum of two and three exponentials as well as a log-normal spectrum of relaxation times. The strong interaction between second-nearest-neighbor atoms in CuMn seems to be essential for SRO kinetics but of minor importance for the value of SRO-induced resistivity change. 相似文献
143.
R. S. Castro S. Prasad R. M. Gomes I. C. E. S. G Lima A. G. Souza T. A. A Melo S. J. G. Lima 《Journal of Thermal Analysis and Calorimetry》2004,75(2):649-654
Co80Nb14B6, Co80Nb12B8 and Co80Nb10B10 amorphous alloys were obtained through the melt-spinning process. The ribbons structure was investigated by X-ray diffractometry
and the crystallization process and the thermal stability were studied by means of differential thermal analysis and thermomechanical
technique. It was observed that the crystallization temperature depends on the alloy composition and occurs in a temperature
range between 420 and 730°C. The coercive field of all alloys was determined by magnetic susceptibility measurements, the
values of which range from 2.78 to 5.95 A m-1.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
144.
A.?CzerwińskiEmail author M.?Grdeń M.??ukaszewski 《Journal of Solid State Electrochemistry》2004,8(6):411-415
The process of hydrogen absorption/desorption in Pd-Pt and Pd-Pt-Rh alloys has been investigated using cyclic voltammetry. Hydrogen absorbed at constant potential was electrooxidized at various scan rates. The charge of hydrogen oxidation has been found to be dependent on the scan rate. The decrease in the oxidation charge observed for low scan rates indicates that, under these conditions, some amount of hydrogen may be removed via a non-electrochemical recombination reaction. The results suggest that the dual mechanism of hydrogen desorption, involving electrochemical oxidation and non-electrochemical recombination, confirmed for pure palladium, is valid also for palladium alloys.Contribution to the 3rd Baltic Conference on Electrochemistry, GDASK-SOBIESZEWO, 23–26 APRIL 2003.Dedicated to the memory of Harry B. Mark, Jr. (February 28, 1934–March 3rd, 2003) 相似文献
145.
Peter D. Mlynek Masaki Kawano Michael A. Kozee Lawrence F. Dahl 《Journal of Cluster Science》2001,12(1):313-338
Reactions of [Ni6(CO)12]2- (1) with CuBr2 have given rise in small yields (10%) to the first example of a close-packed copper-nickel carbonyl cluster; its formulation as [CuxNi35-x(CO)40]5- (with x=3 or 5) is based upon a low-temperature CCD X-ray crystallographic determination coupled with an elemental analysis and X-ray fluorescence measurements. This air-unstable black pentaanion (2) together with one co-crystallized bromide anion, six [NMe4]+ counterions, and one solvated acetone molecule comprise the crystallographic independent part in a monoclinic unit cell of P21/n symmetry (with Z=4). The geometrically unprecedented 35-atom hcp M(A)2M(B)3Ni30 polyhedron of pseudo-D3h symmetry consists of a central 15-atom equilateral 4M(B)3Ni12 triangle that is capped on both sides by two symmetry-related 10-atom equilateral 3M(A)Ni9 triangles. The 35-atom M(A)2M(B)3Ni30 core is encapsulated by 40 COs, whose connectivities, due to an extra CO ligand on one of the three triangular sides, reduce the pseudo D3h symmetry of the metal core to Cs. An elemental analysis via AA and X-ray fluorescence measurements resulted in Cu/Ni ratios of 3.2/31.8 and 3.7/31.3, respectively, that are consistent with the metal core being either Cu5Ni30 (i.e., M(A)=M(B)=Cu) or Cu3Ni32 (i.e., M(A)=Ni; M(B)=Cu). Several attempts to determine the actual stoichiometry of the metal core by use of electrospray FT/MS/ICR measurements were unsuccessful. The maximum metal-core diameter of 2 is ca. 0.41 nm parallel and 0.85 nm perpendicular to the principal 3-fold axis. 相似文献
146.
A.A. Zvyagin 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):351-360
The behavior of charge and spin persistent currents in an integrable lattice ring of strongly correlated electrons with a
magnetic impurity is exactly studied. Our results manifest that the oscillations of charge and spin persistent currents are
similar to the ones, earlier obtained for integrable continuum models with a magnetic impurity. The difference is due to two
(instead of one) Fermi velocities of low-lying excitations. The form of oscillations in the ground state is “saw-tooth”-like,
generic for any multi-particle coherent one-dimensional models. The integrable magnetic impurity introduces net charge and
spin chiralities in the generic integrable lattice system, which determine the initial phase shifts of charge and spin persistent
currents. We show that the magnitude of the charge persistent current in the generic Kondo situation does not depend on the
parameters of the magnetic impurity, unlike the (magneto)resistivity of transport currents.
Received 30 January 2003 / Received in final form 12 March 2003 Published online 11 April 2003
RID="a"
ID="a"e-mail: zvyagin@fy.chalmers.se 相似文献
147.
L. A. Bulavin V. G. Kravets K. L. Vinnichenko D. Yu. Man'ko 《Journal of Applied Spectroscopy》2001,68(5):783-790
The optical properties of amorphous and nanocrystalline tapes of CoFeNiSiB alloys and the ac magnetoresistive effect in them have been investigated. It is shown that the magnetoresistive effect in these alloys increases by about a factor of two after lowtemperature treatment and subsequent laser annealing of these tapes in an external magnetic field. Correlation between the anomalous behavior of the dielectric function of these alloys in the IR region of the spectrum and their magnetoresistive characteristics after thermal annealings has been established. The interrelation between the density of localized electronic states near the Fermi level and the value of the magnetoresistive effect has been revealed. The influence of the induced magnetic anisotropy on the transverse permeability in amorphous and nanocrystalline CoFeNiSiB alloys and, consequently, also on the magnetoresistive effect has been analyzed. 相似文献
148.
Fe
x
Cu100–x
magnetoresistive alloys were produced by mechanical alloying. X-ray diffraction shows fcc structure. The room-temperature Mössbauer spectra evolves from an asymmetrical doublet below x=25%, to a broad magnetic hyperfine field distribution above this concentration. Quadrupole splitting of the doublet varies between 0.48 and 0.57 mm/s, and its isomer shift from 0.16 to 0.29 mm/s. Low-temperature Mössbauer spectroscopy displays a B
hf distribution. Magnetization measurements display different features depending on concentration, from mictomagnetism to ferromagnetism. Low-temperature magnetoresistance is measured. Samples with x20% exhibit larger magnetoresistivity ratios. Bulk and hyperfine magnetic properties are correlated in order to explain magnetoresistivity features of these samples. 相似文献
149.
Characterisation of precipitate phases in magnesium alloys using electron microdiffraction 总被引:1,自引:0,他引:1
Recent results of the characterisation of the structure, morphology and orientation of fine-scale, strengthening precipitate phases in selected magnesium alloys using transmission electron microscopy and microdiffraction are reviewed. The strengthening precipitate phases in Mg–Y–Nd alloys, aged to maximum hardness at 250°C, have been found to include two metastable precipitate phases β′ and β1, and the equilibrium precipitate β. The β′ phase has a globular form, a base-centred orthorhombic structure (potential point group of mmm), and an orientation relationship such that (100)β′//(1
10)α, [001]β′//[0001]α. The β1 phase has an f.c.c. structure (space group
and an orientation relationship that may be described by
(100)β1//[0001]α, and forms as plates parallel to
The β phase has an f.c.c. structure (space group
) and also forms as plates on
with an orientation relationship with the matrix phase that is identical to that observed for β1 phase. Precipitates in Mg–Al alloys, aged isothermally at 200°C, invariably have the b.c.c. structure of the equilibrium precipitate phase β (Mg17Al12). Three orientation relationships have been observed between β and the matrix phase. Most precipitates have an irrational orientation relationship that approximates to the Burger's relationship, (001)β//(0001)α,
and a faceted lath morphology with habit plane parallel to (0001)α. A minor fraction of precipitates posses an orientation relationship that is of the form
and have a prismatic rod morphology. The long axes of these rods are parallel to [0001]α, and their faceted surfaces are parallel to
A few precipitates are observed to have an orientation relationship such that
and a rod shape, with their long axes apparently inclined with respect to [0001]α. 相似文献
Full-size image
Full-size image
150.
P. Billaud J.-R. Huntzinger E. Cottancin J. Lermé M. Pellarin L. Arnaud M. Broyer N. Del Fatti F. Vallée 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):271-274
The extinction spectrum of single silver nanoparticles
with size ranging from 20 to 80 nm is investigated with the spatial
modulation spectroscopy technique using either a tunable laser or a white
lamp as the broadband source. Results are in good agreement with the
prediction of the Mie theory, permitting to extract the nanoparticle size
from the measured absolute value of the optical extinction cross-section. In
contrast, the deduced refractive index of the nanoparticle environment and
the reduction of the electron mean free path show a large dependence on the
precise value of the bulk silver dielectric function. 相似文献