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1.
M. Gómez Berisso P. Pedrazzini J.G. Sereni O. Trovarelli C. Geibel F. Steglich 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):343-349
We present electrical resistivity and specific heat measurements of alloys on the Rh rich side of the phase diagram of the
Ce(Rh1-xPdx)2Si2 system. We compare these results with those obtained at intermediate and low Rh concentrations. The analysis of the concentration
and temperature dependence of the entropy and of the scaling behaviour of C
el
(
T
) and ρ(
T
) clearly confirm a separation of the magnetic phase diagram into two regions: the region x
≤0.3, showing a concentration independent characteristic temperature for the 4
f-electrons with T
0
≈ 45
K, while for x
> 0.3, T0 decreases to T
0
(
x
= 1) ≈ 15
K. At low Pd-content, TN decreases very rapidly from T
N
= 36
K in pure CeRh2Si2 to T
N
= 18
K at x
= 0.1. With higher Pd concentration TN stabilizes at T
N
≈ 15
K whereas the magnitude of the anomalies in C
el
(
T
) and in the susceptibility around TN are further reduced and disappear at x
≈ 0.3. This differs from the behavior found on the Pd-rich side, where TN decreases continuously to zero with increasing Rh content. The pronounced differences observed between both phase boundaries
and the drastic effect of doping on the Rh rich side suggest an itinerant character in CeRh2 Si2, in contrast with the localized character of CePd2Si2. Further evidence for the itinerant character of CeRh2Si2 is given by the ρ(
T
) dependence observed for x
≤0.3, which scales with ρ(
T
) of the prototype itinerant compound YCo2.
Received 31 December 2001 / Received in final form 6 July 2002 Published online 19 December 2002
RID="a"
ID="a"e-mail: berisso@cab.cnea.gov.ar 相似文献
2.
E.F. Wassermann B. Rellinghaus T. Roessel J. Kästner W. Pepperhoff 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):361-365
We measured the thermal expansion and the specific heat of TixFe100-x alloys with x
= 30.5, 32.5 and 35, all with hexagonal C14 laves phase structure (MgZn2) like TiFe2, and determine the temperature dependence of the magnetic contributions to the thermal expansion and the specific heat cmag. For fixed composition and c
mag
(
T
) show the same type of behavior, demonstrating that both anomalies are of the same microscopic nature. They originate from
moment-volume fluctuations (antiferromagnetic Invar-effect) as a comparison with total energy calculations as a function of
atomic volume and moment for TiFe2 reveals.
Received: 26 January 1998 / Accepted: 17 April 1998 相似文献
3.
P. Bonville E. Vincent E. Bauer 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):363-369
We present measurements in the YbCu5-xAlx series, down to the 50 mK range, using 170Yb M?ssbauer absorption spectroscopy and magnetisation measurements. In this series, the hybridisation between the Yb 4
f electrons and the conduction electrons is known to decrease as the Al content x increases. We apply the variational solution of the impurity Kondo problem to the interpretation of our data. We show that
the Kondo temperature can be derived from the measured 4
f quadrupole moment and, for the magnetically ordered compounds (), we obtain the exchange energy as a function of the Al content. Our findings are in general agreement with Doniach's model
describing the onset of magnetic ordering according to the relative values of the Kondo and exchange energy scales.
Received 16 April 1998 相似文献
4.
M. Brando N. Büttgen V. Fritsch J. Hemberger H. Kaps H.-A. Krug von Nidda M. Nicklas K. Pucher W. Trinkl A. Loidl E.W. Scheidt M. Klemm S. Horn 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):289-298
We present susceptibility, microwave resistivity, NMR and heat-capacity results for Li1-xZnx(V1-yTiy)2O4 with 0 ?
x
? 0.3 and 0 ?
y
? 0.3. For all doping levels the susceptibility curves can be fitted with a Curie-Weiss law. The paramagnetic Curie-Weiss temperatures
remain negative with an average value close to that of the pure compound Θ≈ - 36 K. Spin-glass anomalies are observed in the susceptibility, heat-capacity and NMR measurements for both type of dopants.
From the temperature dependence of the spin-lattice relaxation rate we found critical-dynamic behavior in the Zn doped compounds
at the freezing temperatures. For the Ti-doped samples two successive freezing transitions into disordered low-temperature
states can be detected. The temperature dependence of the heat capacity for Zn-doped compounds does not resemble that of canonical
spin glasses and only a small fraction of the total vanadium entropy is frozen at the spin-glass transitions. For pure LiV2O4 the spin-glass transition is completely suppressed. The temperature dependence of the heat capacity for LiV2O4 can be described using a nuclear Schottky contribution and the non-Fermi liquid model, appropriate for a system close to
a spin-glass quantum critical point. Finally an (
x
/
y
,
T
)-phase diagram for the low-doping regime is presented.
Received 16 March 2001 and Received in final form 30 October 2001 相似文献
5.
B. Andraka R. Pietri S.G. Thomas G.R. Stewart E.-W. Scheidt T. Schreiner 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):55-59
A comprehensive study of the relationship between the electronic specific heat coefficient () and the temperature square coefficient (A) of the electrical resistivity for a single, cubic, heavy fermion alloy system, UPt5-xAux is presented. In this alloy system, whose low temperature properties are consistent with the Fermi-liquid behavior, varies by more than a factor of 10 while the corresponding A coefficient changes by a factor larger than 200. A tracks changes in fairly well, but , postulated to have a universal value for heavy fermions, is not constant and varies from about 10-6 (x = 0, 0.5) to 10-5
cm (mol K/mJ)2 (x
> 1.1), thus from a value typical of transition metals to that characteristic of other heavy fermion compounds. We have found a
correlation between and magnetic characteristics such as the paramagnetic Curie-Weiss temperature and the low temperature magnetic susceptibility
divided by .
Received 29 January 1999 相似文献
6.
F. Reynaud A.M. Ghorayeb Y. Ksari N. Menguy A. Stepanov C. Delmas 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):83-90
In this work, results of X-band ESR spectroscopy, ac-magnetic susceptibility and X-ray powder diffraction measurements on
Li1-xNi
1+x
O2 (x
= 0.02 and x
= 0.07) are presented and discussed. While the susceptibility of the compound with x
= 0.02 is shown to follow a Curie-Weiss law, with a Weiss temperature of the order of 30 K, the compound with x
= 0.07 is found to order ferromagnetically below K. However, an additional anomaly is observed in the magnetic properties of this latter compound at around 240 K. We attribute this anomaly to the presence of macroscopic Ni-rich regions which order ferrimagnetically below this temperature.
This phenomenon is different from the bulk ferromagnetism that occurs at much lower temperatures, and allows us to discard
earlier suggestions proposed in the literature in which the 240 K anomaly has been considered as denoting an intrinsic phenomenon.
Received 14 May 1999 and Received in final form 5 August 1999 相似文献
7.
R. Calemczuk J. Riera D. Poilblanc J.-P. Boucher G. Chaboussant L. Lévy O. Piovesana 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):171-174
Specific heat (CV) measurements in the spin-1/2 Cu2(C2H12N2)2Cl4 system under a magnetic field up to H
=8.25 T are reported and compared to the results of numerical calculations based on the 2-leg antiferromagnetic Heisenberg ladder.
While the temperature dependences of both the susceptibility and the low-field specific heat are accurately reproduced by
this model, deviations are observed above the critical field HC1 at which the spin gap closes. In this Quantum High Field phase, the contribution of the low-energy quantum fluctuations are
stronger than in the Heisenberg ladder model. We argue that this enhancement can be attributed to dynamical lattice fluctuations.
Finally, we show that such a Heisenberg ladder, for H
>
H
C1, is unstable, when coupled to the 3D lattice, against a lattice distortion. These results provide an alternative explanation
for the observed low temperature ( K-0.8 K) phase (previously interpreted as a 3D magnetic ordering) as a new type of incommensurate gapped state.
Received: 23 July 1998 / Accepted: 24 August 1998 相似文献
8.
U. Köbler A. Hoser H.A. Graf M.-T. Fernandez-Diaz K. Fischer T. Brückel 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(2):217-224
We present a neutron scattering study of the temperature and composition dependence of the MnO-type superstructure reflection
intensities in the diamagnetically diluted antiferromagnetic compounds EuxSr1-xTe. In these materials antiferromagnetic biquadratic and ferromagnetic three-spin interactions have been identified recently.
These fourth-order non-Heisenberg interactions are able to create their own order parameter which is believed to govern the
order of the transverse moment components and which, hence, is directed perpendicular to the common Heisenberg order parameter.
The observed MnO-type diffraction intensities originate in the sublattice magnetizations, , of both order parameters. Due to the different composition dependencies for biquadratic interaction processes and three-spin interaction processes , the ferromagnetic three-spin interactions dominate for x
>
x
c
=0.85, while for x
<0.85 the antiferromagnetic biquadratic interactions dominate. Associated with this sign change in the fourth-order interaction
sum the transverse order parameter changes from the antiferromagnetic MnO type for x
<0.85 to ferromagnetic for x
>0.85. This is noticed as a sudden decrease of the low-temperature MnO scattering intensities at x
c
=0.85. Although susceptibility measurements reveal clearly a ferromagnetic component for x
>0.85 no ferromagnetic Bragg intensities were observed in standard neutron scattering spectra using EuTe powder samples. We explain
this by the competition of antiferromagnetic biquadratic and ferromagnetic three-spin interactions whereby a disturbed ferromagnetic
superstructure may be generated which gives rise also to weak MnO-type diffraction lines. It is found that the resulting obeys a T2 law until a temperature as large as 0.75TN irrespective of the nature of the transverse order parameter. The T2 law must, hence, be common to both types of order parameter showing that the fourth-order interactions re-define the spin
dynamics of both completely. From the linear composition dependence of the normalized T2 coefficient the existence of three-spin interactions is again confirmed.
Received 23 July 1998 and Received in final form 12 October 1998 相似文献
9.
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
10.
A. Campana R. Cantelli F. Cordero M. Corti A. Rigamonti 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(1):49-54
Anelastic relaxation and 139LaNQR relaxation rates in La2–xSrxCuO4 for Sr content around 2 and 3 percent are discussed in terms of spin and lattice excitations and of the related ordering
processes. It is argued how the phase diagram of La2–xSrxCuO4 at the boundary between the antiferromagnetic (AF) and the spin-glass phase (x
= 0.02) could be more complicate than previously thought, with a transition to a quasi-long range ordered state at K, as indicated by neutron scattering data. On the other hand, the 139LaNQR spectra are compatible with a transition to an AF phase around K, in agreement with the phase diagram commonly accepted in literature. In this case the peaks in NQR and anelastic relaxation
rates around 150 K and 80 K respectively in La1.98Sr0.02CuO4, yield the first evidence of freezing process involving simultaneously lattice and spin excitations, possibly corresponding
to motion of charged stripes.
Received 18 May 2000 and Received in final form 11 July 2000 相似文献
11.
M. Hervieu C. Martin A. Maignan G. Van Tendeloo B. Raveau 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):397-408
The structural transitions that appear in the manganites Ca1-xThxMnO3
versus temperature are studied in connection with their magnetic and transport properties, and compared to those of the Ca1-xLnxMnO3 manganites. An orthorhombic to monoclinic transition is observed for low x values (;this structural distortion, also observed for Ln-doped oxides, is related to the magnetoresistance properties. For higher
x values (), modulated commensurate and incommensurate phases are obtained at low temperature, with , b
=2
a
p and , which are related to Mn3+/Mn4+ charge ordering (CO) phenomena. T values, determined from electron diffraction, are in agreement with those determined from the M
(
T
) curves. The low temperature electron microscopy shows that the CO in those oxides is more complex than in Ln-doped manganites.
In particular, the destabilisation of CO and consequently of the antiferromagnetic interactions is evidenced as the thorium
content increases which may explain the appearance of a spin-glass like behavior for higher x values not seen for Ca1-xSmxMnO3 phases .
Received 2 November 1998 相似文献
12.
13.
S.W.H. Eijt R. Currat J.E. Lorenzo P. Saint-Grégoire B. Hennion Y.M. Vysochanskii 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):169-178
The low frequency lattice dynamics and its relationship to the second order paraelectric-to-ferroelectric transition in Sn2P2S6 is studied. The dispersion branches of the acoustic and lowest lying optical phonons in the a*-c* plane have been obtained in the ferroelectric phase, for x-polarized phonons. Close to the phase transition a considerable softening is found for the lowest optical mode (Px), comparable to the behaviour observed in previous Raman investigations. As found previously in Sn2P2Se6, a strong coupling between the TO(Px) and TA(uxz) phonons is observed, although, apparently, not strong enough to lead to an incommensurate phase. The soft TO(Px) mode at the zone center is observed. The temperature dependence of its frequency and damping shows that the transition is
not entirely displacive. At low temperatures an unusual apparent negative LO-TO splitting is observed which is shown to arise
from the coupling of the x-polarized soft mode to the nearby z-polarized optical phonon. For comparison, the soft TO(Px) dispersion in the a*-b* plane is measured in both the paraelectric and ferroelectric phases. Consistent frequency changes and LO-TO splitting are
observed, revealing a significant interaction between the TA(uyx) and LA(uxx) acoustics branches and the TO and LO soft optic branches, respectively. In contrast, the nearby y-polarized optic branch shows almost no temperature dependence. Finally, the influence of piezoelectric effects on the limiting
acoustic slopes in the ferroelectric phase is discussed.
Received: 11 May 1998 / Revised and Accepted: 15 June 1998 相似文献
14.
F. Tedoldi A. Campana P. Carretta 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):219-223
μSR measurements in the antiferromagnetic (AF) phase of Ni1-xLixO for are reported. While in pure NiO the muon longitudinal depolarization rate is found almost temperature independent, in the Li-doped compounds broad maxima around 130 K are observed. These maxima are
associated with the progressive freezing of the spin fluctuations of S
=1/2 defects induced by the localization of the extra-holes. From the temperature dependence of and the stretched exponential form of the depolarization, insights on the distribution of correlation times for the fluctuating
field at the muon site are derived.
Received: 27 April 1998 / Received in final form and Accepted: 21 August 1998 相似文献
15.
I. Souza Azevedo E. Baggio Saitovitch M. Hücker B. Büchner H. Micklitz 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):313-315
57Fe M?ssbauer effect studies of La1.65Eu0.20Sr0.15CuO4 doped with 0.5 at% 57Fe performed in the temperature region 300 K >
T
> 4.2 K give an onset temperature for magnetic ordering of K. This temperature practically is the same as that found in Nd doped La2-xSrxCuO4. It indicates that the magnetic ordering temperature in the LTT phase of rare earth (RE) doped La2-xSrxCuO4 is independent of the RE moment. The direction of the 57Fe magnetic moment in the magnetically ordered state is within the CuO2 plane, while it has been found to be parallel to the c-axis in Nd doped La2-xSrxCuO4.
Received: 23 June 1998 / Accepted: 14 July 1998 相似文献
16.
P. Estrela A. de Visser T. Naka F.R. de Boer L.C.J. Pereira 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(4):449-454
The effect of hydrostatic pressure ( p
? 1.8 GPa) on the non-Fermi liquid state of U2Pt2In is investigated by electrical resistivity measurements in the temperature interval 0.3-300 K. The experiments were carried
out on single-crystals with the current along (
I
||
c
) and perpendicular (
I
||
a
) to the tetragonal axis. The pressure effect is strongly current-direction dependent. For I
||
a we observe a rapid recovery of the Fermi-liquid T2-term with pressure. A comparison of the data with the magnetotransport theory of Rosch provides evidence for the location
of U2Pt2In at an antiferromagnetic quantum critical point. For I
||
c the resistivity increases under pressure, indicating the enhancement of an additional scattering mechanism.
Received 2 March 2001 and Received in final form 29 June 2001 相似文献
17.
H. von Löhneysen A. Neubert T. Pietrus A. Schröder O. Stockert U. Tutsch M. Loewenhaupt A. Rosch P. Wölfle 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):447-455
We report on extensive elastic neutron scattering to determine the wave vector of the magnetic order in CeCu6-xAux single crystals for x
> 0.1. For all values of x investigated (0.2, 0.3, 0.5, 1.0) we find long-range incommensurate antiferromagnetic order with an ordering vector (0.625
0.275) for x
=0.2, nearly unchanged for x
=0.3, and (0.59) for x
=0.5, staying roughly the same for x
=1.0. In addition, short-range correlations are observed for x
=0.2, reminiscent of those found previously for x
=0.1. The ordered magnetic moment is found to increase rapidly for small x, and more slowly for the larger x values. The increase of the specific-heat anomaly at the ordering temperature with x is in qualitative accord with this behavior. Finally, data of the electrical resistivity for current flow along the three
crystallographic directions are presented, showing a clear signature of the magnetic order. A theoretical interpretation of
the interplay of magnetic order and transport in terms of (i) the partial suppression of the Kondo effect by the staggered
magnetization and (ii) the anisotropic band structure induced by the staggered field is shown to account well for the data,
provided the ordering vector is close to 2
k
F, where k
F is a typical Fermi momentum.
Received: 20 February 1998 / Accepted: 17 April 1998 相似文献
18.
Z. Kovacevic R. Hayn N.M. Plakida 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):487-495
In the framework of the cell-perturbation method for the original p-d model an effective two-band Hubbard model for the CuO2 plane with Zn impurities is derived. Zn impurities are modelled by Wannir oxygen one-hole states at vacant Cu sites. The model is based on the results of band structure calculations carried out
within the local-density approximation. Further reduction to an extended t-J model shows a large ferromagnetic superexchange interaction between the Cu spin with the nearest virtual oxygen spin in the
Zn cell.
Received 17 November 1998 相似文献
19.
M.B. Zölfl Th. Maier Th. Pruschke J. Keller 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):47-53
We study one-particle spectra and the electronic band-structure of a CuO
2
-plane within the three-band Hubbard model. The Dynamical Mean-Field Theory (DMFT) is used to solve the many particle problem.
The calculations show that the optical gap is given by excitations from the lower Hubbard band into the so called Zhang-Rice singlet band. The optical gap turns out to be considerably smaller than the bare charge transfer energy () for a typical set of parameters, which is in agreement with experiment. We also investigate the dependence of the shape
of the Fermi surface on the different hopping parameters t
CuO and t
OO. A value t
OO
/
t
CuO
>0 leads to a Fermi surface surrounding the M point.
Received 21 September 1998 and Received in final form 8 June 1999 相似文献
20.
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