共查询到20条相似文献,搜索用时 31 毫秒
1.
U. Busolt E. Cottancin L. Socaciu H. Röhr T. Leisner L. Wöste 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):297-300
The diffusion and aggregation of preformed Agn-clusters (
n
= 2-9) deposited onto a highly oriented pyrolytic graphite (HOPG) substrate is studied by two-photon-photoemission (2PPE). The sample
is irradiated with ultrashort laser pulse pairs and the kinetic energy of the emitted photoelectrons is analyzed in a magnetic
bottle type time-of-flight spectrometer. During annealing of the sample from 100 K up to room temperature, nanoparticles are
formed on the surface by diffusion and aggregation of the silver clusters. A steep increase of the total photoelectron yield
at a sample temperature of about 150 K is explained by the excitation of plasmons in the silver nanoparticles. From the kinetic
energy distribution of the photoelectrons we deduce a strong variation of the work function of the sample during the formation
of the nanoparticles, which is attributed to a quantum size effect. 相似文献
2.
Research was carried out to estimate the possibility of determining the direction and strength of the ancient geomagnetic
field (H
an
) by natural remanent magnetization (I
n
) of nine oriented samples from traps of the Minor Botuoba Region (Yakutia) aged 260 Ma. Five samples (Pi-10, K-4, K-6, 315–13,
and Ki-2) are characterized by negative polarity of In, while four samples (nos. 334-5, 331–2, 315–11, 299–2) have positive polarity as does the recent geomagnetic field in this
region. The ferrimagnetic constituent of the samples with reverse I
n
polarity appears to be quite variable: samples K-4 and K-5 are characterized by low Curie points (T
c
≈ 200°C) of the ferrimagnetic phase, sample Ki-2 contains single-phase oxidized titanomagnetite with T
c
≈ 310°C, and the T
c
of the Pi-10 ferrimagnetic phase is 540°C. Hence, it may be concluded that the primary remanent magnetization of the first
two samples was formed in a reverse polarity field. These samples also may be used to determine the paleostrength of the geomagnetic
field. The properties of traps containing single-phase oxidized (sample Ki-2) and disintegrated (sample Pi-10) titanomagnetite
require additional investigation. Samples with positive In polarities are characterized by the self-reversal phenomenon upon thermal demagnetization of the natural remanent magnetization,
which was most likely caused by the occurrence of titanomagnetite exsolution textures in ferrimagnetic grains. The paleoinformation
value of the I
n
of these samples is doubtful. 相似文献
3.
T. Niemöller N. Ichikawa T. Frello H. Hünnefeld N.H. Andersen S. Uchida J.R. Schneider J.M. Tranquada 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(4):509-513
Superstructure reflections due to the ordering of holes into stripes in have been studied with high energy X-ray diffraction. These reflections have been observed clearly for the first time in
a sample which is superconducting at low temperatures ( K). The stripe peaks vanish above 62(5) K whereas the magnetic signal of the stripe ordering which has been seen with neutrons
before is already suppressed at K. Our results confirm that the ordering of spins and holes is driven by the charges as it is found in the case of La1.6-xNd0.4SrxCuO4 at the doping level of x
=0.12.
Received 27 April 1999 相似文献
4.
J. Kortus M.R. Pederson C.S. Hellberg S.N. Khanna 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):177-180
Based on first-principles all-electron density-functional calculations we report the electronic structure and magnetic ordering
of the molecular magnet Fe8 and the V15 spin system. The ferrimagnetic ordering with total spin S
= 10 of the eight iron atoms in the Fe8 cluster agrees well with experimental results from polarized neutron data. In comparison the low spin system V15 shows a spin S
= 1/2 ground state which is also found from our calculations.
Received 30 October 2000 相似文献
5.
M.S. Wertheim 《Molecular physics》2013,111(1):211-223
The theory of the static dielectric constant of non-polar fluids is re-examined using graph-theoretical techniques. A sample of arbitrary shape in an applied static electric field E 0 is considered. The non-local tensor which transforms from E 0 to the electrostatic polarization P is expressed as a sum of graphs. The relation appears simpler in terms of the inverse tensor, which is also obtained as a sum of graphs. Agreement with classical electrostatics is then manifest, and the shape-independence of the dielectric constant follows. An approximation suitable for numerical work is formulated, and a simplified version is solved analytically. The results are similar to those for fluids of rigid polar molecules in the Mean Spherical Model approximation. Reasons for both the similarities and the differences are given. 相似文献
6.
《Composite Interfaces》2013,20(7):425-432
Abstract ZnS nanoparticles and Mn2+-doped ZnS nanoparticles were prepared by a reverse micelle reaction system. In addition, ZnS and Mn2+-doped ZnS nanoparticles were modified with poly(vinyl alcohol) (PVA) and 1-dodecanethiol (C12H25SH). The average particle size of the ZnS sample is determined around 2.3 nm by using the well-known Scherrer equation, which is in accordance with the results obtained from UV–vis and TEM analysis. Fluorescence intensity of the Mn2+-doped ZnS nanoparticles increases with increasing Mn2+ content compared with undoped ZnS nanoparticles, and coating PVA can also make fluorescence intensity increase. Different Zn2+/S2- or C12H25SH/Zn2+ can affect intensity of PL emission peak and its position, which is discussed in this paper. 相似文献
7.
The thermopower in the YBa2−x
LaxCu3Oy system (x=0–0.5) has been studied. An analysis made in terms of the narrow-band model revealed trends in the variation of the main
band parameters with increasing lanthanum concentration. The dependence of the conduction band width on lanthanum concentration
was found to pass through a weak minimum at x=0.05–0.1, which correlates in position with the maximum in the concentration dependences of the critical temperature and
degree of sample orthorhombicity. The results obtained and their comparison with Fe, Co→Cu substitution data permit a conclusion
that the main factor affecting the properties of the YBa2Cu3Oy system under nonisovalent substitution of various cations is the increasing disorder in the chain-oxygen subsystem caused
by increasing impurity content.
Fiz. Tverd. Tela (St. Petersburg) 40, 17–22 (January 1998) 相似文献
8.
S. Sadewasser J.S. Schilling A. Knizhnik G.M. Reisner Y. Eckstein 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):15-20
Hydrostatic pressure studies on the tetragonal 123 superconductor (La1-xCax) (Ba1.75-xLa0.25+x)Cu3Oy for x
=0.1 and variable oxygen content y show that increases rapidly under pressure (+5 K/GPa) for underdoped, optimally doped and overdoped samples. This points to a common cause for the pressure-induced changes
in the superconductivity at all levels of doping, with negligible effects from charge transfer. Weak relaxation behavior in
is observed only for the most underdoped sample.
Received 26 August 1999 相似文献
9.
C. Langhammer F. Steglich M. Lang T. Sasaki 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):413-416
We report low-temperature measurements 0.07
K
?
T
? 2 K of the specific heat, C, of the perovskite superconductor Sr2RuO4. Based on a detailed analysis of our data with respect to both sample quality (as measured by T
c
= 0.43
K
- 1.17 K) and magnetic-field dependence, it is shown that the electronic contribution to the specific heat, which contains the desired
information on the gap structure, is superimposed by at least two additional contributions: a Schottky-type hump at T
≈ 0.1 - 0.2 K and a low-temperature upturn in C
/
T at T
< 0.1 K. We discuss possible origins of these additional contributions and their implications for the interpretation of low-temperature
C
(
T
) data.
Received 23 August 2001 相似文献
10.
A. Bombardi N. Kernavanois P. Dalmas de Réotier G.H. Lander J.P. Sanchez A. Yaouanc P. Burlet E. Lelièvre-Berna A. Rogalev O. Vogt K. Mattenberger 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):547-552
In the UxLa1-xS system there is an abrupt loss of the long-range ferromagnetic ordering found in pure US at a critical concentration x
c
∼ 0.57, which is far above the percolation limit. As the magnetic ground state in such a system can be strongly affected by small
variations of the 5f localization, we have investigated a set of samples with different x by polarized neutron diffraction and X-ray magnetic circular dichroism (XMCD). The neutron results are consistent with early
measurements performed on pure US. Even at the lowest U content (x
= 0.15, below x
c
) the shape of the induced form factor (f
(
Q
)) is comparable with that found for x
= 1 and is well reproduced by either a U4+ or a U3+ state. The ratio between the orbital and the effective spin moments in the XMCD measurements confirms this result, but the
evolution of the shape at the M5 edge suggests an abrupt change in the distribution of the electrons (holes) in the 5
f density of states around x
c
.
Received 31 January 2001 相似文献
11.
I. F. Voloshin A. V. Kalinov L. M. Fisher K. I. Kugel’ A. L. Rakhmanov 《Journal of Experimental and Theoretical Physics》1997,84(6):1177-1185
Measurements of the imaginary part of the ac magnetic susceptibility of single crystals and melt-textured samples of YBa2Cu3Ox (YBCO) at T=77 K in a magnetic field ranging between 1 and 20 kOe are reported. If the dc magnetic field H
dc is rotated in the ab plane of the sample, the magnetic susceptibility and critical current density j
c have peaks corresponding to the magnetic field aligned with twin boundaries. Peaks in the curve of j
c versus magnetic field are observed at angles corresponding to these peaks, where
AH
dc in a wide range of magnetic fields. The results have been interpreted in terms of the theory describing twin boundaries as
a system of quasi-planar pinning sites. The pinning is strong if the elastic displacements of flux lines are of the order
of the vortex lattice constant d
f. These displacements decrease with the magnetic field because of the decrease in d
f, and the contribution of the elastic energy to the Gibbs potential is reduced accordingly, which is the cause of the peak
effect.
Zh. éksp. Teor. Fiz. 111, 2158–2174 (June 1997) 相似文献
12.
M. A. Zelikman 《Technical Physics》1997,42(9):1019-1026
The behavior of planar (laminar) vortices in a three-dimensional, ordered Josephson medium as a function of the parameter
I, which is proportional to the critical junction current and the cell size, is investigated with allowance for pinning due
to the cellular structure of the medium. The minimum possible distances between two isolated vortices are calculated. A system
of vortices formed in a sample in a monotonically increasing external magnetic field is analyzed. The minimum distance from
the outermost vortex to the nearest neighbor is proportional to I
−1.1. For I⩽1.3 each vortex contains a single flux quantum Φ0, and the distance between them does not decrease in closer proximity to the boundary but remains approximately constant,
implying that the magnetic field does not depend on the coordinate in the region penetrated by vortices. These facts contradict
the generally accepted Bean model. The sample magnetization curve has a form typical of type II superconductors. Allowance
for pinning raises the critical field H
c and induces a sudden jump in the curve at H=H
c.
Zh. Tekh. Fiz. 67, 38–46 (September 1997) 相似文献
13.
R.M. Mueller U. Köbler K. Fischer 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(2):207-216
For the ferromagnets EuS and GdMg, in which fourth-order exchange interactions (i.e. biquadratic, three-spin and four-spin interactions) have been identified, the deviation of the spontaneous magnetization
with respect to the T
=0 value is shown to follow a T2 law instead of the famous T3/2 law expected for a Heisenberg ferromagnet. Moreover, the observed T2 law holds for temperatures as large as 0.8TC and the extrapolated magnetization value for does not conform to ferromagnetic saturation. This is because the fourth-order exchange interactions generate a second order-parameter
which is assumed to govern the order of the transverse moment components. These moment components have a finite expectation
value for at the expense of the Heisenberg order parameter. Like the spontaneous magnetization, the critical field curves B
c
(
T
) of the metamagnet EuSe and the antiferromagnet EuTe also start decreasing with a T2 term for . It is argued that the T2 law is a consequence of the fourth-order exchange interactions. This is shown experimentally by a study of the critical field
curves [0pt] pertinent to the longitudinal (Heisenberg) order-parameter in the diamagnetically diluted antiferromagnets EuxSr1-xTe. In this solid solution series a particular composition of x
c
=0.85 exists at which the different fourth-order interaction processes compensate each other in the high temperature average. As
a consequence, an EuxSr1-xTe sample with x
=0.85 meets the requirements of a Heisenberg antiferromagnet at least if a quantity is considered for which the high-temperature
average over all fourth-order interactions is decisive. This seems to be the case for the critical field curve [0pt] which
gives the phase boundary to the paramagnetic phase. In fact, a crossover from a T2 to a T3/2 law is observed for [0pt] on approaching xc. This, we believe, shows the frequently observed T2 law is caused by the fourth-order interactions.
Received 23 July 1998 and Received in final form 12 October 1998 相似文献
14.
Abstract When tracing the fluxes of N compounds (especially N oxides) and carbon dioxide in the system soil-atmosphere and applying 15N and 13C, it is necessary to simultaneously determine both the concentration of the substances and their isotopic composition. GC separation (packed column) was coupled to a mass spectrometer by a special interface. Variable sample volumes can be delivered by changing the split by means of the interface in front of the MS. Thus, both the concentration of a gaseous compound and its 15N content can be measured. Supplying sample volumes in a range between 5 μl and 5 ml, it is possible to measure both components of high content (e.g., nitrogen) and at the lower ppm(v)-content (e.g., dinitrogen oxide) in the air. Measurements of N2, N2O, NO and CO2 are demonstrated, too. 相似文献
15.
V. F. Gantmakher V. V. Sinitsyn G. É. Tsydynzhapov N. A. Doroshenko V. P. D’yakonov 《JETP Letters》1997,65(6):502-508
An initially nonsuperconducting ceramic sample with the composition NdBa2Cu3O6+x
is brought, by means of pressure and quenching, to a state with a high carrier density and a superconducting transition,
after which it is returned to the initial state by gradual annealing in several steps. The evolution of the magnetoresistance
of the sample showed that even in the most resistive state realized in the experiment the superconducting interaction influences
the resistance of the sample at fields all the way up to 5–6 T. In an 8 T field the change in resistance in this state in
the temperature interval from 0.4 K to 20 K is described well by a logarithmic law ΔR∝ logT.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 6, 475–480 (25 March 1997) 相似文献
16.
T.J. Smith H. Capellmann R.K. Kremer K-U. Neumann K.R.A. Ziebeck 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):341-347
A polarised neutron scattering investigation has been carried out on a powder sample of CuGeO3 within the temperature range of 1.5 K to 600 K. The magnetic scattering has been separated from all other contributions by
using polarised neutrons and polarisation analysis and placed onto an absolute scale. At low temperatures the long wavelength
components of the paramagnetic response are suppressed consistent with the formation of Cu dimers in which the magnetic moments
are correlated antiferromagnetically. This form of the scattering persists to temperatures well above the dimerisation temperature
T
sp
∼ 14 K. However as the temperature is raised the intensity of the long wavelength spin fluctuations increases and above ∼150 K they are the dominant feature in the wave vector dependence of the response. At all temperatures the observed scattering
extrapolates smoothly to the Q
= 0 value given by the uniform susceptibility. Consequently the thermal variation of the uniform susceptibility arises from the
evolution of the long wavelength magnetic fluctuations. At large wave vectors the energy dependence of the scattering revealed
that the response occurs below 16 meV in agreement with the reported maximum magnetic excitation energy at the zone boundary
in the ground state. However the total magnetic scattering is significantly less than that expected for a local moment system
suggesting that the spectrum of thermal and quantum fluctuations overlap.
Received 30 May 2000 and Received in final form 22 March 2001 相似文献
17.
Abstract Onset of electric current has been detected on illuminating the near–contact regions of RbAg4I5 crystals. The spectral and temperature characteristics of this current have been studied. A method is proposed for studying the spectrum of electronic states in the α-phase of the RbAg4I5 crystal. The dependence of the magnitude of the current and its spectral characteristics on the particular region of the RbAg4I5 crystal which is exposed to the light was used for the analysis of the variations in the distribution of defects along the length of the sample and the processes which occur near the electrode-(solid electrolyte) junctions. 相似文献
18.
A study is made of the x-ray photoemission spectra of low-energy electrons (E
kin=0–30 eV) and its dependence on the way in which the potentials are applied to the entrance system of the analyzer. It is
shown that under certain experimental conditions the spectrum consists solely of electrons emitted from the sample. The x-ray
photoemission spectrum of pure silver is found to have a fine structure, which disappears when a surface layer of carbon or
oxygen is deposited on the surface. The spectrum then takes on the “cascade” form. A possible interpretation of the fine structure
is suggested in the framework of band theory.
Zh. Tekh. Fiz. 67, 73–77 (March 1997) 相似文献
19.
Abstract The correlation time τD of the rotational motion of OH? centers in NaCl was studied for two different OH?-concentrations (44 ppm and 220 ppm) between 0.5 K and 16 K by 23Na nuclear spin relaxation measurements. The correlation time in the sample containing 44 ppm OH? is given by phonon-assisted tunneling of isolated defects, whereas the OH?-motion in the sample containing 220 ppm can be described by a coupled ensemble of quantum mechanical hindered rotators below a critical temperature which is determined by the strength of the interaction between the OH? dipoles. 相似文献
20.
M. Jourdan N. Blümer H. Adrian 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):25-30
Superconducting SrTiO
3 - δ
was obtained by annealing single crystalline SrTiO3 samples in ultra high vacuum. An analysis of the V
(
I
) characteristics revealed very small critical currents I
c
which can be traced back to an unavoidable doping inhomogeneity. R
(
T
) curves were measured for a range of magnetic fields B at I
≪
I
c
, thereby probing only the sample regions with the highest doping level. The resulting curves B
c2
(
T
) show upward curvature, both at small and strong doping. These results are discussed in the context of bipolaronic and conventional
superconductivity with Fermi surface anisotropy. We conclude that the special superconducting properties of SrTiO
3 - δ
can be related to its Fermi surface and compare this finding with properties of the recently discovered superconductor MgB2.
Received 4 December 2002 / Received in final form 10 March 2003 Published online 23 May 2003
RID="a"
ID="a"e-mail: jourdan@uni-mainz.de 相似文献