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1.
S. Rubin M. Holdenried H. Micklitz 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):23-28
Well-defined granular Co/Ag films have been prepared by the co-deposition of in-beam prepared Co clusters and Ag atoms. In
this way we were able to study the giant magnetoresistance (GMR) as a function of mean Co cluster size for a fixed Co cluster volume fraction vcl as well as a function of vcl for a fixed . Mean Co cluster size has been varied between and 6.9 nm, Co cluster volume fraction between 5 and 43%. The GMR was measured in-situ at T=4.2 K in magnetic fields 1.2 T. The analysis of the GMR data obtained from these studies clearly shows that spin-dependent scattering at the Co-cluster/Ag-matrix
interface is the only relevant scattering mechanism causing the GMR in our well-defined samples.
Received: 21 April 1998 / Received in final form: 17 May 1998 /
Accepted: 18 May 1998 相似文献
2.
R. Guirado-López D. Spanjaard M.-C. Desjonquères A.M. Oleś 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):437-446
We analyze the stability of magnetic states obtained within the tight-binding model for cubooctahedral (Oh) and icosahedral (Ih) clusters of early 4d (Y, Zr, Nb, Mo, and Tc) transition metals. Several metastable magnetic clusters are identified which suggests the existence
of multiple magnetic solutions in realistic systems. A bulk-like parabolic behavior is observed for the binding energy of
Oh and Ih clusters as a function of the atomic number along the 4
d-series. The charge transfer on the central atom changes sign, while the average magnetic moments present an oscillatory behavior
as a function of the number of d electrons in the cluster. Our results are in agreement with other theoretical calculations.
Received: 20 November 1997 / Received in final form: 9 March 1998 / Accepted: 30 March 1998 相似文献
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5.
P. Bonville J. A. Hodges Z. Hossain R. Nagarajan S. K. Dhar L. C. Gupta E. Alleno C. Godart 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):377-383
We present magnetic properties of the three-band Hubbard model in the para- and antiferromagnetic phase on a hypercubic lattice
calculated with the Dynamical Mean-Field Theory (DMFT). To allow for solutions with broken spin-symmetry we extended the approach
to lattices with AB-like structure. Above a critical sublattice magnetization one can observe rich structures in the spectral-functions similar to the t-J model which can be related to the well known bound states for one hole in the Neél-background. In addition to the one-particle
properties we discuss the static spin-susceptibility in the paramagnetic state at the points and for different dopings . The -T-phase-diagram exhibits an enhanced stability of the antiferromagnetic state for electron-doped systems in comparison to hole-doped.
This asymmetry in the phase diagram is in qualitative agreement with experiments for high-Tc materials.
Received: 28 May 1998 / Revised and Accepted: 14 September 1998 相似文献
6.
H. Mizuseki Y. Jin Y. Kawazoe L.T. Wille 《Applied Physics A: Materials Science & Processing》2001,73(6):731-735
Thin films obtained by cluster deposition have attracted strong attention both as a new manufacturing technique to realize
high-density magnetic recording media and to create systems with unique magnetic properties. Because the film’s features are
influenced by the cluster properties during the flight path, the relevant physical scale to be studied is as large as centimeters.
In this paper, a new model of cluster growth processes based on a combination of the Direct Simulation Monte Carlo (DSMC)
method and the cluster growth model is introduced to examine the effects of experimental conditions on cluster growth by an
adiabatic expansion process. From the macroscopic viewpoint, we simulate the behavior of clusters and inert gas in the flight
path under different experimental conditions. The internal energy of the cluster, which consists of rotational and vibrational
energies, is limited by the binding energy which depends on the cluster size. These internal and binding energies are used
as criteria of the cluster growth. The binding energy is estimated by surface and volume terms. Several types of size distribution
of generated clusters under various conditions are obtained by the present model. The results of the present numerical simulations
reveal that the size distribution is strongly related to the experimental conditions and can be controlled.
Received: 23 January 2001 / Accepted: 3 May 2001 / Published online: 30 August 2001 相似文献
7.
T. Boutreux 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):419-424
We present the generalization of a theoretical model for segregation of granular mixtures due to surface flows, published
in J. Phys. I France 6, 1295 (1996). Our generalized model is valid for grains differing by their size and/or their surface properties; in the present
paper, we describe the case of two species with the same surface properties but two different sizes. The rolling stream is
assumed to be homogeneous. Exchanges between the grains at rest and the rolling stream are modelized via binary collisions.
The model predicts that during the filling of a two-dimensional silo, continuous segregation appears inside the static phase: small (respectively large) grains tend to stop uphill (respectively downhill), although
both species remain present everywhere. This fits the observations when the size difference between the species is small.
When the size difference is large, a different regime is observed. We argue that in this case, segregation occurs directly inside the rolling stream.
Received: 25 February 1998 / Received in final form and Accepted: 6 July 1998 相似文献
8.
L. Zhang W. L. Zhong C. L. Wang Y. P. Peng Y. G. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):565-573
The size effect of the dielectric properties and the barrier height was investigated in the ferroelectric solid solution BaxSr1-xTiO3 system. The decrease of the grain size causes the suppression of the ferroelectricity, and the increase of the relaxation
frequency. Barrier heights increase with increasing grain size. The result is analogous to magnetic phase transitions in nanocrystals
and other solid-solid phase transitions in nanocrystals. It suggests a general rule that may be of use in the discovery of
new metastable phases. An explanation of this phenomenon was given by an electric potential model that agrees well with the
experimental results. For BaxSr1-xTiO3 system, the decrease of xcauses the decrease of the barrier height.
Received 3 August 1998 and Received in final form 22 November 1998 相似文献
9.
Y. Shimizu S. Sawada K.S. Ikeda 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):365-372
“Spontaneous alloying” observed by Yasuda, Mori et al. for metallic small clusters is simulated using classical Hamiltonian dynamics. Very rapid alloying occurs homogeneously and
cooperatively starting from the solid phase of the cluster if the heat of solution is negative and the size of cluster is
less than a critical size. Analysis of 2D models reveals that the alloying rate obeys an Arrhenius-type law, which predicts
the alloying time much less than second at room temperature. Evidences manifesting that the spontaneous alloying proceeds in the solid phase without melting are
also presented. The simulation reproduces the essential features of the experiments.
Received: 2 March 1998 / Revised: 21 May 1998 / Accepted: 28 May 1998 相似文献
10.
M.-H. Schaffner F. Patthey U. Heiz W.-D. Schneider O. Kuffer H.-V. Roy P. Fayet J.K. Gimzewski R. Berndt 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(1):79-82
The emission of photons in the visible wavelength range from mass-selected Ag+
n, Cu+
n, Pt+
n and Pd+
n () clusters is observed. Photons are detected 10-4 s after the cluster generation in a sputter source. The emission intensities display distinct variations with cluster size
and material. The observations are interpreted in terms of the decay of metastable states which are excited during the high-energy
sputtering process used for the generation of these clusters.
Received: 28 October 1997 / Revised: 5 January 1998 / Accepted: 30 January 1998 相似文献
11.
In the past different models for the magnetic salt vanadyl pyrophosphate (VO)2P2O7 were discussed. Neither a spin ladder nor an alternating chain are capable to describe recently measured magnetic excitations.
In this paper we propose a 2D model that fits better to experimental observations.
Received: 29 May 1998 / Received in final form: 25 September 1998 / Accepted: 30 September 1998 相似文献
12.
E. Muñoz-Sandoval J. Dorantes-Dávila G.M. Pastor 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(1):89-96
The electronic and magnetic properties of clusters are investigated in the framework of the Hubbard model by treating electron
correlations effects in a saddle-point slave-boson approximation. The size dependent single-particle spectrum is calculated
using a third moment real-space expansion of the local density of states. Results for the magnetic moments, magnetic order,
average number of double occupations and hopping renormalizations are given as a function of the local coordination number
z, for different representative values of the Coulomb interaction strength U/t and band filling n. Several transitions between paramagnetic, ferromagnetic and antiferromagnetic behaviors are obtained as a function of z. The environment dependence of the magnetic behavior and of the degree of electron delocalization is analyzed. Advantages
and limitations of the present approach are discussed.
Received: 8 January 1998 / Revised: 22 June 1998 / Accepted: 6 August 1998 相似文献
13.
G. Chaboussant M.-H. Julien Y. Fagot-Revurat M. Hanson L.P. Lévy C. Berthier M. Horvatic O. Piovesana 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(2):167-181
In a magnetic field, spin-ladders undergo two zero-temperature phase transitions at the critical fields Hc1 and Hc2. An experimental review of static and dynamical properties of spin-ladders close to these critical points is presented. The
scaling functions, universal to all quantum critical points in one-dimension, are extracted from (a) the thermodynamic quantities
(magnetization) and (b) the dynamical functions (NMR relaxation). A simple mapping of strongly coupled spin ladders in a magnetic
field on the exactly solvable XXZ model enables to make detailed fits and gives an overall understanding of a broad class of quantum magnets in their gapless
phase (between Hc1 and Hc2). In this phase, the low temperature divergence of the NMR relaxation demonstrates its Luttinger liquid nature as well as
the novel quantum critical regime at higher temperature. The general behavior close these quantum critical points can be tied
to known models of quantum magnetism.
Received: 13 March 1998 / Received in final form and Accepted: 21 July 1998 相似文献
14.
G. Mattei F. Toigo 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(3):245-256
The effect of non-local norm-conserving pseudo-potentials on the static and dynamic properties of Nan and Lin cluster with n=6,8 is investigated in the frame of self-consistent LDA calculations with spherically averaged ionic density (SAPS model).
A comparison with previous calculations which use local pseudo-potentials as well with uniform averaged non-local pseudo-jellium
calculation has been carried out. A better quantitative agreement with experiments has been found in the calculation of the
photoresponse cross-section with respect to either simple jellium or pseudo-jellium model, even in very small clusters, where
deviations from sphericity are not negligible.
Received: 3 March 1998 / Received in final form and Accepted: 2 June 1998 相似文献
15.
P. Schieffer C. Krembel M.-C. Hanf M.-H. Tuilier P. Wetzel G. Gewinner K. Hricovini 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(2):165-168
We studied the magnetic properties of ultra-thin Mn films deposited on Ag (001) held at 80 K with soft X-ray absorption and
magnetic circular dichroism. The observed shape and branching ratio of the Mn 2p absorption edge as a function of Mn coverage demonstrate that, up to , the Mn adopts a stable high spin state similar to the Mn atom Hund's rule 6
S
5/2
ground state. Above this coverage a rapid transition from localized high spin to itinerant low spin behavior of the Mn 3d electrons is evidenced. Magnetic circular dichroism shows no sign of long range ferromagnetic order in these films at 80
K. The data, first confirm the large atomic-like local magnetic moment, and second are in line with the in-plane antiferromagnetic order, reported recently (Phys. Rev. B 57, 1141 (1998)), for Mn in the nearly ideal on-top Mn monolayer formed by 0.9 ML deposited at 80 K.
Received: 4 May 1998 相似文献
16.
T. Schenkel A.V. Barnes A.V. Hamza D.H. Schneider 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(3):297-302
Cluster ion emission from a variety of surfaces upon impact of highly charged ions is investigated by time-of-flight secondary
ion mass spectrometry. The yield of cluster ions as a function of cluster size for and surface follow a power law decline with exponent approaching the -2 limit of the ”equilibrium” and ”shock wave” cluster emission
models. While the decline of the cluster ion emission with cluster size is an exponential decay for highly oriented pyrolytic
graphite upon impact, the decline is more gradual than for impact, such that at the relative cluster yield is 1000 times higher.
Received: 22 April 1997 / Revised: 29 December 1997 / Accepted: 19 January 1998 相似文献
17.
L. Benguigui F. Boué 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):439-444
Small angle neutron scattering of polyacrylamide solutions and gels is presented for different polymer and cross link concentrations.
The gels are analyzed in connection with their elastic properties. For less than 11% of polymer concentration and for small
cross link contents , it was found that the gels are no more heterogeneous than the solutions. This corresponds to the range of where the elastic modulus increases with . For larger cross link contents when the elastic modulus decreases if increases, the sample appears to be strongly heterogeneous with a large size distribution of the inhomogeneities. The results
are compared with the recent model of Oshmyan and Benguigui of the elastic properties of the polyacrylamide gels. Thus a relation
can be proposed between the observation of the inhomogeneities by scattering and the mechanical properties
Received 30 December 1997 and Received in final form 26 June 1998 相似文献
18.
J.M. Mestdagh M. Berdah N. Auby C. Dedonder-Lardeux C. Jouvet S. Martrenchard-Barra D. Solgadi J.P. Visticot 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):291-302
The photodissociation of a chlorine molecule in the environment of a xenon cluster has been studied experimentally using the
real time pump and probe technique through the formation of an XeCl reaction product. The photodissociating system is probed
in such a way that the movement of a single chlorine atom in the xenon environment is detected. Various XenCl2 cluster sizes have been investigated leading to the distinction between uncapped, half-capped and doubly capped structures
for these clusters. These structures have a profound influence on the photodissociation dynamics. Retrapping of one chlorine
atomic fragment and stabilization of the XeCl reaction product is only observed for the half and doubly capped clusters. The
experimental work is complemented by classical molecular dynamics calculations to get a full picture of the photodissociation.
Received: 17 February 1998 / Received in final form and Accepted: 28 July 1998 相似文献
19.
E. Rastelli A. Tassi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):285-289
Dipolar spin-spin interactions play a crucial role as for the magnetic order in the compounds of the RBa2Cu3O6+x family, (R = Dy, Er, Nd). However, inelastic neutron scattering data observed in ErBa2Cu3O7 can be explained only if exchange interactions in addition to dipolar ones are taken into account.
Received: 12 January 1998 / Received in final form: 26 March 1998 / Accepted: 10 April 1998 相似文献
20.
P. Entel R. Meyer K. Kadau H.C. Herper E. Hoffmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):379-388
Results are presented of first-principles total-energy calculations and molecular-dynamics simulations of structural transformations
in magnetic transition metal alloys like Fe1-xNix. While first-principles calculations allow to identify those structures having the lower total energy, molecular-dynamics
simulations can be used to trace out the dependence of the transformation on temperature, composition, concentration of defects
etc. We have used the method of the semi-empiric embedded-atom potential in the molecular-dynamics simulations which yields remarkable
good results for the structural changes.
Received: 3 February 1998 / Revised: 4 May 1998 / Accepted: 24 June 1998 相似文献