共查询到20条相似文献,搜索用时 15 毫秒
1.
W. Westerburg F. Martin P.J.M. van Bentum J.A.A.J. Perenboom G. Jakob 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(3):509-513
We measured the temperature dependence of the linear high field Hall resistivity of ( K) and ( K) thin films in the temperature range from 4 K up to 360 K in magnetic fields up to 20 T. At low temperatures we find a
charge-carrier density of 1.3 and 1.4 holes per unit cell for the Ca- and Sr-doped compound, respectively. In this temperature
range electron-magnon scattering contributes to the longitudinal resistivity. At the ferromagnetic transition temperature
a dramatic drop in the number of charge-carriers n down to 0.6 holes per unit cell, accompanied by an increase in unit cell volume, is observed. Corrections of the Hall data
due to a non saturated magnetic state will lead a more pronounced charge-carrier density collapse.
Received 22 July 1999 and Received in final form 7 October 1999 相似文献
2.
R. Citro M. Marinaro 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(2):235-242
The spin magnetic susceptibility of the p-d model is calculated by means of a perturbation theory in the hybridization term V through a generalized cumulant expansion (GCE). The analysis is approached from the paramagnetic metallic phase. The results
qualitatively reproduce some unusual magnetic properties in the normal state of the hole-doped cuprates, supporting the scenario
of a Van Hove singularity near the Fermi level.
Received 15 October 1998 and Received in final form 24 March 1999 相似文献
3.
A. Goujon O. Roubeau F. Varret A. Dolbecq A. Bleuzen M. Verdaguer 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):115-124
We studied the photo-excitation process, the relaxation of the photo-excited state towards the stable state, and the photo-induced
magnetic properties of the Prussian blue analogue Rb0.52Co [Fe(CN)6]0.84, 2.3 H2O. Magnetic, M?ssbauer and reflectivity measurements have been performed during and after illumination. The efficiency of
the photo-excitation device is maximum at nm. The process, however, is severely hindered by bulk absorption of the light; it is rapidly completed at the surface of
the sample and then proceeds slowly in the bulk. Under the effect of photo-excitation the system turns from a dia- to a ferri-
magnet, with a value K, indicative of the transformation of the material due to the following optical electron transfer: Thermal relaxation towards the stable electronic state is observed in the 95-110 K temperature interval, obeying a self-accelerated
kinetics. At low temperature, a weak, non-exponential, relaxation is detected. These features are discussed in terms of co-operative
effects in the frontal process of photo- excitation. The peculiarities of a photo-excited state created below the magnetic
ordering temperature are discussed. A metastable magnetic state has been observed in low fields, denoted “Raw Photo-Induced
State" (RPI), with a magnetization curve in-between the field-cooled and zero-field-cooled curves.
Received 12 March 1999 and Received in final form 11 December 1999 相似文献
4.
5.
M. Pinterić T. Vuletić M. Lončarić S. Tomić J.U. von Schütz 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):487-493
We report a detailed characterization of an unique 3-fold commensurate insulating state in single crystals of the organic
– inorganic d hybrid Cu(DMe-DCNQI)2 systems with deuterated and partially deuterated DCNQI ring, by means of low-frequency dielectric spectroscopy. A broad relaxation
mode of strength centred at kHz is observed in the hysteresis temperature region in which the insulating phase coexists with metallic islands. At lower
temperatures, outside the nucleation range, the relaxation narrows, approaching a Debye-like form for an overdamped response
of a system with a single degree of freedom. Both, the relaxation strength and the mean relaxation time () are much larger than that expected for single-particle excitations. These features suggest the origin of the dielectric
relaxation as an intrinsic property of the N = 3 charge density wave state.
Received 1 December 1999 and Received in final form 5 April 2000 相似文献
6.
S. Paschen E. Felder H.R. Ott 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(2):169-176
We present measurements of the specific heat, the electrical resistivity, the Hall effect, and the magnetic susceptibility
of CeAuAl3, a new heavy-electron compound that crystallizes in an ordered derivative of the tetragonal BaAl4-type structure. For comparison we have also done some of these measurements on the isostructural non-magnetic reference compound
LaAuAl3, which appears to be a simple metal. Below K, CeAuAl3 orders antiferromagnetically and below 1K, we encounter Fermi liquid behaviour with considerably enhanced effective masses,
i.e., a quadratic temperature dependence of the resistivity with a large prefactor and a sizable linear-in-T contribution to the specific heat. This linear-in-T contribution increases by more than a factor 50 from its value at to its value at . Consequently CeAuAl3 develops a heavy-electron ground state, coexisting with antiferromagnetic order. The small energy scales involved in the
problem make CeAuAl3 a good candidate for tuning it, by varying external parameters, towards a quantum critical point. At high temperatures we
observe local moment behaviour. From the temperature dependence of the magnetic susceptibility and the specific heat we have
derived the crystalline-electric-field-split level scheme of the J
=5/2 multiplet. Distinct features in the electrical resistivity provide additional evidence for this level splitting.
Received: 6 November 1997 / Accepted: 17 November 1997 相似文献
7.
C. Stockinger W. Markowitsch W. Lang W. Kula R. Sobolewski 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):301-311
We report our studies on the superconducting and normal-state properties of metallic thin films ( 52 K) exposed to long-term white-light illumination (photodoping). It was observed that the effects of photoexcitation strongly
depended on the temperature at which the photodoping was performed. At low temperatures, both the Hall mobility and the Hall
number were photoenhanced, whereas, at temperatures slightly below room temperature, the Hall mobility initially showed an
abrupt increase followed by a long-term decrease, and the Hall number increased even stronger than at low temperatures. The
enhancement of the film's superconducting transition temperature Tc, caused by photodoping, exhibited the same temperature dependence as the enhancement of the Hall number, being largest ( 2.6 K) at high temperatures. From the asynchronous behavior of the Hall quantities, we conclude that both the photoassisted
oxygen ordering and charge transfer mechanisms contribute to photodoping. The relative contributions of both mechanisms and,
thus, the electronic properties of the photoexcited state are strongly temperature dependent. Studies of the relaxation of
the photoexcited state at 290 K showed an unexpectedly short relaxation time of the Hall mobility after termination of the
illumination. The relaxation saturated somewhat below the initial, undoped value, similarly to the decrease of the Hall mobility,
observed upon long illumination. These latter findings give evidence for a competition between the oxygen ordering and thermal
disordering processes during and after the photoexcitation in the high-temperature range.
Received: 13 October 1997 / Accepted: 19 November 1997 相似文献
8.
Magnetoresistances and magnetic entropy changes associated with negative lattice expansions in NaZn13-type compounds LaFeCoSi 下载免费PDF全文
Magnetoresistances and magnetic entropy changes in NaZn13-type compounds La(Fel-xCox)11.9Si1.1 (x=0.04, 0.06, and 0.08) with Curie temperatures of 243 K, 274 K, and 301 K, respectively, are studied. The ferromagnetic ordering is accompanied by a negative lattice expansion. Large magnetic entropy changes in a wide temperature range from ~230 K to ~320 K are achieved. Raising Co content increases the Curie temperature but weakens the magnetovolume effect, thereby causing a decrease in magnetic entropy change. These materials exhibit a metallic character below Tc, whereas the electrical resistance decreases abruptly and then recovers the metal-like behaviour above Tc. Application of a magnetic field retains the transitions via increasing the ferromagnetic ordering temperature. An isothermal increase in magnetic field leads to an increase in electrical resistance at temperatures near but above Tc, which is a consequence of the field-induced metamagnetic transition from a paramagnetic state to a ferromagnetic state. 相似文献
9.
A. E. Kar’kin V. V. Shchennikov B. N. Goshchitskii S. E. Danilov V. L. Arbuzov 《Journal of Experimental and Theoretical Physics》1998,86(5):976-982
Using single-crystal samples of Bi2Te3 bombarded by 5-MeV electrons at a temperature of 250 K, we study the electrical resistivity and the Hall effect in the temperature
range 1.7–370 K and the Shubnikov-de Haas effect at T=4.2 K in magnetic fields up to 14 T. We find that electron bombardment of Bi2Te3 crystals results in a transition from the metallic p-type state to the metallic state with a Fermi surface. Annealing at 350 K eliminates the radiation defects and restores the
p-type metallic conductance.
Zh. éksp. Teor. Fiz. 113, 1787–1798 (May 1998) 相似文献
10.
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
11.
A. T. Zheleznyak V.M. Yakovenko 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):385-399
We present a heuristic, semiphenomenological model of the anomalous temperature (T) dependence of resistivity recently observed experimentally in the quasi-one-dimensional (Q1D) organic conductors of the family in moderately strong magnetic fields. We suggest that a Q1D conductor behaves like an insulator (), when its effective dimensionality is one, and like a metal (), when its effective dimensionality is greater than one. Applying a magnetic field reduces the effective dimensionality of
the system and switches the temperature dependence of resistivity between the insulating and metallic laws depending on the
magnitude and orientation of the magnetic field. We critically analyze whether various microscopic models suggested in literature
can produce such a behavior and find that none of the models is fully satisfactory. In particular, we perform detailed analytical
and numerical calculations within the scenario of magnetic-field-induced spin-density-wave precursor effect suggested by Gor'kov
and find that the theoretical results do not agree with the experimental observations.
Received 20 October 1998 相似文献
12.
Th. Brückel D. Hupfeld J. Strempfer W. Caliebe K. Mattenberger A. Stunault N. Bernhoeft G.J. McIntyre 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(4):475-490
We report on X-ray resonance exchange and neutron scattering of metallic GdS. At the LII and L III absorption edges of Gd, resonance enhancements of more than two orders of magnitude over the non-resonant magnetic scattering
are observed. Polarisation analysis proves that these enhancements are due to dipolar transitions from the 2p to the 5d states. The branching ratio between the LII and L III edges of 2.5 suggests a polarisation of the 5d electrons in the ground state. The antiferromagnetic order is of type II in the fcc lattice. Single crystal diffraction of
hot neutrons suggests that the spin direction lies within the (111) planes with a value for the sublattice magnetisation of
6.51(3) . The critical exponent for the sublattice magnetisation has a value of β = 0.38(2) in agreement with a pure Heisenberg model.
Above T
N, a sharp component persists in the critical diffuse scattering. Lattice distortions give indications for two additional low-temperature
phase transitions at about 49 K and 32 K. We argue that these transitions are not connected to spin reorientations and discuss
the possible influence of fourth-order exchange interactions.
Received 19 November 1999 and Received in final form 12 December 2000 相似文献
13.
L. Brossard R. Clerac C. Coulon M. Tokumoto T. Ziman D.K. Petrov V.N. Laukhin M.J. Naughton A. Audouard F. Goze A. Kobayashi H. Kobayashi P. Cassoux 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(4):439-452
In order to understand the magnetic field-induced restoration of a highly conductive state in , static (SQUID) and dynamic (ESR and AFR) magnetization measurements were performed on polycrystalline samples and single
crystals, respectively. In addition, cantilever and resistivity measurements under steady fields were performed. While the
metal-insulator transition curve of the () phase diagram exhibits a first order character, a “spin-flop” transition line divides the insulating state when the magnetic
field is applied along the easy axis of magnetization. The effects of a RKKY-type indirect exchange and of applied magnetic
field are described within the framework of a generalized Kondo lattice, namely two chains of localised spins coupled through the itinerant spins of the 2D sheets of BETS. The calculations, which can incorporate intramolecular
electron correlations within a mean field theory, are in qualitative agreement with the field induced transition from the
antiferromagnetic insulating ground state to a canted one, i.e. a not fully oriented paramagnetic, but metallic state.
Received: 6 August 1997 / Received: 5 November 1997 / Accepted: 10 November 1997 相似文献
14.
T. Kodaira S. Inoue Y. Murakami 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):267-270
Arrayed cationic K clusters including one 4s-electron in each cluster, i.e., Km+1
m+, were incorporated into α-cages of zeolite LTA with Si/Al=1.5. Although no magnetic phase transition was observed regarding
the temperature (T) dependence of magnetic susceptibilities originating from the 4s-electron spins (χspin) between 2 and 300 K, the χspin-T curve could be fitted by the sum of magnetic susceptibilities based on the Curie-Weiss law and Pauli paramagnetism. A possible
explanation of this behavior is the existence of a narrow energy band formed out of 1s-cluster orbitals of arrayed K clusters,
and the existence of a finite density of state at the Fermi energy. 相似文献
15.
J.W. Taylor T.J. Smith K.H. Andersen H. Capellmann R.K. Kremer A. Simon O. Schärpf K.-U. Neumann K.R.A. Ziebeck 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(2):199-207
The magnetic response in V
2
O
3
has been investigated using polarised neutron scattering with polarisation analysis. Measurements were carried out at three
temperatures corresponding to the antiferromagnetic insulating ground state, the metallic phase and the high temperature metallic
phase. At the first order metal insulator transition there is a dramatic change in the magnetic response with the metallic
and high temperature metallic phases being characterised by ferromagnetic spatial correlations of the paramagnetic response.
The establishment of ferromagnetic correlations at the metal insulator transition accounts for the abrupt jump in the uniform
susceptibility. It is proposed that the differentiation of the V-V distances across the edges of VO
6
octahedra is of critical importance for the change in electronic conductivity but also for the establishment of the spatial
correlations. The gradual high temperature evolution of the conductivity then occurs by the reduction in the vanadium d overlap
brought about by thermal expansion. The first order reduction in atomic volume which occurs on the establishment of the metallic
phase results from an instability of the vanadium local moment arising from the change in electronic structure.
Received 7 April 1999 相似文献
16.
The magnetic susceptibility of hydrogen-doped partially crystalline (Zr76Ni24)1−xHx metallic glasses
I. Kokanovi? 《Journal of magnetism and magnetic materials》2009,321(13):1985-1989
The magnetizations of Zr76Ni24 metallic glass and hydrogen-doped partially crystalline (Zr76Ni24)1−xHx metallic glasses have been measured in the temperature range 10-300 K and magnetic fields up to 2 T for various dopant concentrations (x=0, 0.024, 0.043, 0.054). It is found that the samples are paramagnetic and magnetic susceptibility at room temperature, χ(300 K), shows a nonmonotonic behaviour upon hydrogenation. The values of χ(300 K) of the hydrogen-doped partially crystalline (Zr76Ni24)1−xHx metallic glasses are reduced with increase in hydrogen content up to x=0.043, whereas for x=0.054, an enhancement of χ(300 K) has been revealed. The magnetic susceptibility is weakly temperature dependent down to 110 K, below which an increase is observed. A shallow minimum exists between 90 and 120 K. The form and magnitude of the observed temperature dependence of the magnetic susceptibility are well accounted for by the sum of the quantum corrections to the magnetic susceptibility. Hydrogen reduces the electronic diffusion constant and influences strongly the quantum interference at defects, slowing down the spin diffusion and enhancing the magnetic susceptibility in the temperature range from 110 down to 10 K. 相似文献
17.
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
18.
The Hubbard model on fcc-type lattices is studied in the dynamical mean-field theory of infinite spatial dimensions. At intermediate
interaction strength finite temperature Quantum Monte Carlo calculations yield a second order phase transition to a highly
polarized, metallic ferromagnetic state. The Curie temperatures are calculated as a function of electronic density and interaction
strength. A necessary condition for ferromagnetism is a density of state with large spectral weight near one of the band edges.
Received: 6 August 1997 / Accepted: 20 August 1997 相似文献
19.
Structure and properties of some glass-forming liquid alloys 总被引:1,自引:0,他引:1
U. Dahlborg M. Calvo-Dahlborg P.S. Popel V.E. Sidorov 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):639-648
Some physical properties (kinematic viscosity, surface tension and magnetic susceptibility) of some Fe-based metallic melts
of easily glass-forming alloys have been measured during heating and subsequent cooling. The results indicate that molten
liquid metallic alloys undergo a number of structural transformations ranging from the initial microheterogeneous state formed
after melting up to the true solution state. Studies by small angle neutron scattering on a eutectic SnPb melt confirm this
conclusion in that two families of different sizes have been seen, one in the range 1 to 2 nm and one of size larger than
100 nm. Both kind of particles have relatively sharp interfaces and the size of the smaller particles is found to depend on
temperature.
Received 25 February 1999 and Received in final form 28 October 1999 相似文献
20.
M. Pinterić M. Miljak N. Biškup O. Milat I. Aviani S. Tomić D. Schweitzer W. Strunz I. Heinen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(2):217-225
We report a detailed characterization of the magnetism and AC transport in single crystals of the organic conductor -(BEDT-TTF)2Cu[N(CN)2]Cl by means of magnetic anisotropy measurements and low-frequency dielectric spectroscopy. Magnetic anisotropy obeys Curie-Weiss
law with negative Curie-Weiss temperature in the temperature range 300 K-70 K. An antiferromagnetic transition with concomitant
canted antiferromagnetic state is established at 22 K. A large hysteresis in the spin-flop transition and magnetic field reversal
of the weak ferromagnetic magnetization are documented for the first time. A broad dielectric relaxation mode of moderate
strength () emerges at 32 K, and weakens with temperature. The mean relaxation time, much larger than that expected for single-particle
excitations, is thermally activated in a manner similar to the DC conductivity and saturates below 22 K. These features suggest
the origin of the broad relaxation as an intrinsic property of the weak ferromagnetic ground state. We propose a charged domain
wall in a random ferromagnetic domain structure as the relaxation entity. We argue that the observed features might be well
described if Dzyaloshinsky-Moriya interaction is taken into account. A Debye relaxation with similar temperature dependence
was also observed and seems to be related to an additional ferromagnetic-like, most probably, field-induced phase. We tentatively
associate this phase, whose tiny contribution was sample dependent, with a Cu2+ magnetic subsystem.
Received 15 June 1998 and Received in final form 1 February 1999 相似文献