共查询到20条相似文献,搜索用时 31 毫秒
1.
V. E. Arkhipov V. E. Startsev V. P. Dyakina J. Klamut Ya. M. Mukovskii A. Czopnik 《JETP Letters》1998,68(1):42-46
Magnetization measurements were performed on a lanthanum manganite La0.9Sr0.1MnO3 single crystal in the temperature interval 4.2–300 K and magnetic field interval 50 Oe-55 kOe in two sample cooling regimes:
1) cooling down to 4.2 K in a high (55 kOe) magnetic field, and 2) cooling in a “zero” field. It is shown that the temperature
dependences of the magnetization M(T) are substantially different in these regimes. Pronounced anomalies of M(T) were observed at temperatures T*=103 K and T
c
=145 K. The first anomaly is attributed to a structural transition, while the second one corresponds to a ferromagnet-paramagnet
phase transition. The magnetization of a La0.9Sr0.1MnO3 single crystal in the cooling regimes studied shows typical “spin-glass” behavior.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 39–43 (10 July 1998) 相似文献
2.
J. Kästner W. Petry S.M. Shapiro A. Zheludev J. Neuhaus Th. Roessel E.F. Wassermann H. Bach 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):641-648
The acoustic phonon dispersions of two Invar crystals , one ordered with the () structure, the other disordered fcc, have been investigated between 3.4 K and 470 K by inelastic and elastic neutron scattering.
For the ordered crystal, pronounced softening of the whole
phonon branch is observed on cooling below the Curie temperature. Particularly strong phonon softening at the M-point zone
boundary of the structure leads to a displacive, antiferrodistortive phase transition at low temperatures. For the disordered crystal, much
weaker softening of the
phonons is observed and restricted to the region near the Brillouin zone center, where increasing elastic scattering with
decreasing temperature indicates the growth of local tetragonal strain. This strain is considered as a typical precursor of
the transformation to bct martensite. Specific heat measurements, performed at low temperatures on both crystals confirm the
neutron scattering results and reveal considerable enhancement of the low energy phonon density of states in the ordered crystal.
Received 18 January 1999 相似文献
3.
Inelastic neutron scattering experiments to determine phonon density of states of coherent scattering samples of polycrystalline
complex solids are generally intensity-limited and therefore are feasible only at high flux facilities. Phonon density of
states of the monoclinic phase of tetracyanoethylene at 300 K, obtained using the medium resolution triple axis spectrometer
at the new Indian medium flux reactor Dhruva are reported here. The raw data is converted to the “neutron weighted” phonon
density of states by applying suitable corrections. Comparison made with results from a theoretical calculation based on a
semirigid molecule model of lattice dynamics is fair. Results from Dhruva are also consistent with that obtained (to be published)
at the high flux pulsed neutron source (ISIS) of the Rutherford Appleton Laboratory in United Kingdom. 相似文献
4.
Pencer J Mills T Anghel V Krueger S Epand RM Katsaras J 《The European physical journal. E, Soft matter》2005,18(4):447-458
Using coarse grained models of heterogeneous vesicles we
demonstrate the potential for small-angle neutron scattering
(SANS) to detect and distinguish between two different categories
of lateral segregation: 1) unilamellar vesicles (ULV) containing a
single domain and 2) the formation of several small domains or
“clusters” (~10 nm in radius) on a ULV. Exploiting the
unique sensitivity of neutron scattering to differences between
hydrogen and deuterium, we show that the liquid ordered (lo)
DPPC-rich phase can be selectively labeled using chain deuterated
dipalymitoyl phosphatidylcholine (dDPPC), which greatly
facilitates the use of SANS to detect membrane domains. SANS
experiments are then performed in order to detect and
characterize, on nanometer length scales, lateral heterogeneities,
or so-called “rafts”, in ~30 nm radius low polydispersity
ULV made up of ternary mixtures of phospholipids and cholesterol.
For 1:1:1 DOPC:DPPC:cholesterol (DDC) ULV we find evidence for the
formation of lateral heterogeneities on cooling below 30 °C. These heterogeneities do not appear when DOPC is
replaced by SOPC. Fits to the experimental data using coarse
grained models show that, at room temperature, DDC ULV each
exhibit approximately 30 domains with average radii of ~10 nm. 相似文献
5.
D. M. Trots A. N. Skomorokhov M. Knapp H. Fuess 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(4):507-512
Results of simultaneous thermal analysis (STA),
synchrotron powder diffraction (in the range 300–973 K) and inelastic
neutron scattering (at 285 and 505 K) on non-superionic β- and
superionic α-AgCuSe are reported. The sample is stable in argon on
heating. The volume change at the superionic phase transition is about
5%. A model for the average structure of α-AgCuSe is proposed. No
anomalies in the temperature dependence of the parameters of the average
structure were revealed. Ionic conductivity in α-AgCuSe can
originate from cation jumps in “skewed” 〈100 〉 directions between
nearest-neighbour tetrahedral sites via the peripheries of the octahedral
cavities. A correlation between the temperature dependence of the cation
redistribution in α-AgCuSe and the temperature dependence of the
ionic conductivity is supposed. Various contributions (anharmonic effects,
time-average static disorder and phonon-phonon scattering) to the widths of
individual phonons upon temperature increase lead to pronounced changes in
the neutron-weighted densities of states of β- and α-AgCuSe
and accompany the superionic phase transition as well. 相似文献
6.
Ola Hartmann Erik Lidström Mikael Ekström Roger Wäppling L. Asch G.M. Kalvius 《Hyperfine Interactions》1997,104(1-4):293-299
The ferromagnetic cone phase of erbium has been studied with μSR. Two precessing muon signals were observed with nearly equal
intensities at T\approx15\ K. At lower temperatures, one of the signals is gradually reduced and disappeared below 5 K. The
two observed muon frequencies and their depolarisation behaviour show that the magnetic structure deduced from neutron and
X‐ray scattering must be modified and that a “squaring up” of the structure is likely to occur as the temperature is lowered.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
Jean-Paul Boucher 《Hyperfine Interactions》1989,49(1-4):423-438
Topological excitations play a crucial role in antiferromagnetic chains. In the present review, we focus on the dynamical
fluctuations induced by these quasi-particles, trying to show how they can be observed experimentally. In particular the pulsed
nuclear magnetic resonance (NMR) technique can probe these fluctuations at very low frequency. In the same context, neutron
spin echo (NSE) measurements are briefly mentioned. A discussion of soliton magnetic resonance (SMR) measurements in also
presented: they reveal the existence of internal precessions in the solitons (Dyons) and they show that the uniform (q=0) soliton modes can be detected directly. The experimental data to be discussed were obtained on three compounds: TMMC which
provides good examples for “broad” solitons and CsCoCl3 for “narrow” solitons. A discussion of NMR data obtained with NENP is given in the context of the Haldane's conjecture.
Member of Equipe de Recherche CNRS no. 216. 相似文献
8.
J.-F. Berret D.C. Roux P. Lindner 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):67-77
We have investigated the simple shear flow behavior of wormlike micelles using small-angle neutron scattering and mechanical
measurements. Ternary surfactant solutions made of cetylpyridinium chloride, hexanol and brine (0.2 M NaCl) and hereafter
abbreviated as CPCl-Hex were studied in the concentrated regime, . In a preliminary report (Berret et al. [#!ref16!#]), the discontinuity of slope observed in the shear stress versus shear rate curve was interpreted in terms of first-order phase transition between an isotropic state and a shear-induced
nematic state ( transition). At the transition rate, , the solution exhibits a macroscopic phase separation into viscous and fluid layers (inhomogeneous shear flow). Above a second
characteristic shear rate, the flow becomes homogeneous again, the sheared solution being nematic only. The neutron patterns
obtained in the two-state inhomogeneous region have been re-examined. Based on a consistent analysis of both orientational
and translational degrees of freedom related to the wormlike micelles, we emphasize new features for the transition. In the present paper, the shear rate variations of the relative proportions of each phase in the two-state region,
as well as the viscosity ratio between isotropic and nematic phases are derived. We demonstrate in addition that slightly
above the transition rate, the shear induced nematic phase is already strongly oriented, with an order parameter P
2
= 0.65. The orientational state is that of a nematic flow-oriented monodomain. Finally, from the locations of the neutron
scattering maxima for each isotropic and nematic contributions, we evaluate the concentrations for each phase and and derived a dynamical phase diagram of CPCl-Hex, in terms of the stress
versus
and . According to the classification by Schmitt et al. [#!ref22!#], the transition observed in CPCl-Hex micellar solutions could result from a positive flow-concentration coupling, in agreement
with the observed monotonically increasing shear stress in the two-phase region.
Received: 16 February 1998 / Revised: 18 February 1998 /
Accepted: 24 May 1998 相似文献
9.
The results of measurements of the time dependences of the dielectric constant of TlGaSe2 in the commensurate ferroelectric phase are presented. From the result of the observation of the decay of ε at different stabilized temperatures below the commensurate phase transition temperature after cooling from the incommensurate phase, the presence of two different characteristic relaxation time constants with the same temperature behaviour has been revealed. This peculiarity is considered as a result of a coexistence of two polar sublattices in the temperature range below 110 K. According to these results, the previously reported dielectric anomaly at about 103 K is considered as a final lock-in phase transition accompanied by the forming of the antiferroelectric state in TlGaSe2. 相似文献
10.
It has been shown that the dynamic superlattice of pulsed complexes of soliton vibrations or, actually, a “soliton crystal”
is self-organized in crystalline materials at high levels of thermal and dynamic excitations of atomic vibrations. The results
obtained have been adapted to the alpha uranium crystal system. It has been demonstrated that the atom bombardment of crystalline
materials leads to the generation of beams of nonlinear subsonic and supersonic soliton and breather waves. The breathers
and solitons initiate threshold kinetic processes of defect formation, such as surface vibrations and evaporation of surface
atoms, multiple reflection of bombarding atoms, and restructuring of nanocrystals. The results obtained can be used in experimental
investigations of microdynamics of materials under high dynamic and temperature loads by the neutron and ion scattering methods. 相似文献
11.
We study the forced aspiration of small ( mm) and large ( cm) liquid drops, deposited on prewetted porous membranes, and pumped mechanically with a constant current J. Two kinds of membranes are used where the pores are i) disconnected, cylindrical and calibrated or ii) interconnected “sponge-like”.
Whatever the size of the drops and the intensity J of the current, two suction regimes are observed versus time: 1) a “locked” regime, when the drop is pinned, with a dynamic contact angle decreasing from advancing () to finite receding () contact angle; 2) an “unlocked” regime, where the contour line recedes with a constant contact angle closed to . In both regimes, the shape of the drop remains quasistatic, during the suction process, i.e. a spherical cap for small drops and a flat “gravity pancake” for large ones.
Received 19 January 2000 相似文献
12.
?mer Kavaklolu Baruch Schneider 《International Journal of Infrared and Millimeter Waves》2008,29(4):329-352
A rigorous analytical representation for the multiple scattering coefficients of the fields radiated by an infinite grating
of dielectric circular cylinders excited by an obliquely incident plane electromagnetic wave is derived in terms of the “well-known
scattering coefficients of an isolated dielectric cylinder at oblique incidence” and “Schl?milch series”. In addition, a generalized
sum-integral grating equation is acquired for the multiple scattered amplitude of a cylinder at oblique incidence in the grating
in terms of the scattering coefficients of the insulating dielectric circular cylinder at oblique incidence.
相似文献
13.
L. Elcoro J.M. Perez-Mato 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(1):85-89
The diffraction properties of a quenched Al-Mg alloy which has been recently termed as a “cubic quasicrystal” are quantitatively
reanalyzed. It is shown that the phase can be interpreted within the superspace formalism as an ordinary incommensurately modulated structure. The cubic six-dimensional superspace group that describes its symmetry properties has
been determined. The additional inflation symmetry features exhibited by the diffraction diagram can be summed up by its invariance
for the inflation factor , but this property has its origin in the specific value of the modulus of the modulation wave vectors, which is composition
dependent. Other particular values of this modulus can give rise to similar scaling properties. Further experiments are required
to ellucidate if the mentioned inflation symmetry is a fortuitous situation in a composition dependent wave vector, or has
indeed the physical significance which would allow to describe the system as a “cubic quasicrystal”.
Received: 25 June 1998 / Received in final form and Accepted: 23 September 1998 相似文献
14.
This letter reports microwave dielectric measurements performed in the antiferroelectric phase of NaNbO3 ceramics from 100 to 450 K. Remarkable dielectric relaxation was found within the antiferroelectric phase and in the vicinity of the ferroelectric-antiferroelectric phase transition. Such dielectric relaxation process was associated with relaxations of polar nanoregions with strong relaxor-like characteristic. In addition, the microwave dielectric measurements also revealed an unexpected and unusual anomaly in the relaxation strength, which was related to a disruption of the antiferroelectric order induced by a possible AFE-AFE phase transition. 相似文献
15.
M. Geoghegan F. Boué G. Bacri A. Menelle D.G. Bucknall 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(1):83-96
We have used neutron reflectometry to measure interfacial widths between two polystyrene films, where either one or both films
are crosslinked. The observed interfacial width between two networks is larger than the size expected for “dangling ends”,
which suggests motion of heterogeneous regions of the networks. In the case when one of the networks is replaced by a linear
polymer, the interfacial profile can be asymmetric with a diffusion “front” of linear polymer penetrating the network to a
length scale of up to 200 ?. In the case of a more densely crosslinked network and a high molecular weight linear polymer
the interface is symmetric implying negligible penetration.
Received: 4 December 1996 / Revised: 13 October 1997 / Accepted: 23 December 1997 相似文献
16.
É. Falcon S. Fauve C. Laroche 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):183-186
We report experimental results on the behavior of an ensemble of inelastically colliding particles, excited by a vibrated
piston in a vertical cylinder. When the particle number is increased, we observe a transition from a regime where the particles
have erratic motions (“granular gas”) to a collective behavior where all the particles bounce like a nearly solid body. In
the gas-like regime, we measure the density of particles as a function of the altitude and the pressure as a function of the
number N of particles. The atmosphere is found to be exponential far enough from the piston, and the “granular temperature”, T, dependence on the piston velocity, V, is of the form , where is a decreasing function of N. This may explain previous conflicting numerical results.
Received 1 February 1999 相似文献
17.
18.
E. Kogan M. Auslender M. Kaveh 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):373-376
Localization and dephasing of conduction electrons in a low carrier density ferromagnet due to scattering on magnetic fluctuations
is considered. We claim the existence of the “mobility edge”, which separates the states with fast diffusion and the states
with slow diffusion; the latter is determined by the dephasing time. When the “mobility edge” crosses the Fermi energy a large
and sharp change of conductivity is observed. The theory provides an explanation for the observed temperature dependence of
conductivity in ferromagnetic semiconductors and manganite pyrochlores.
Received 17 January 1999 and Received in final form 12 March 1999 相似文献
19.
Three related aspects of the magnetic phase diagram are presented here: the first deals with the disruption of the antiferromagnetic
order in the electron rich phase obtained by Ce doping, the second concern the role of Bi planes as a sink-buffer of carriers,
the third focuses the magnetization vs. temperature curves in a variety of different bilayer materials as seen by the muons
and discusses the “anomalous” behaviour in relation to theoretical predictions and neutron scattering data. 相似文献
20.
E. Holland-Moritz W. Weber G. Michels W. Schlabitz A. Mewis Ch. Sauer H. Mutka 《Zeitschrift für Physik B Condensed Matter》1989,77(1):105-110
We report on inelastic neutron scattering experiments on EuNi2P2 prepared from153Eu-isotopes. The sample was checked by Mössbauer spectroscopy; a satellite phase of about 4% was found. The neutron scattering experiment was performed with thermal neutrons. AboveT=50 K a strong quasielastic magnetic line was detected with a nearly temperature independent width of about 6 meV. At low temperatures the spectrum changes to an inelastic character with a distinctQ-dependence in the intensity. For comparison static susceptibility and magnetization measurements were performed down to 250 mK. 相似文献