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1.
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
2.
P. Vonlanthen J.L. Gavilano B. Ambrosini H.R. Ott Y. Aoki H. Sugawara H. Sato 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(1):15-20
We report the results of 69Ga- and 71Ga-NMR measurements on NdGa2 at temperatures between 0.1 and and in applied magnetic fields between zero and 74 kOe. NdGa2 orders antiferromagnetically below and undergoes several metamagnetic transitions in external magnetic fields. In zero applied magnetic field and below the temperature dependence of the spin-lattice relaxation rate T1
-1
(
T
) shows a large linear-in-T term, about two orders of magnitude higher than for the reference compound LaGa2. This strong enhancement confirms the presence of low-energy excitations in the antiferromagnetic phase of NdGa2 as was previously indicated by specific heat data. Above , T1
-1
(
T
) is dominated by an exponential term, which we associate with excitations between the lowest energy levels of the f-electron system. The separation of these energy levels is determined by exchange, crystal-field and Zeeman interactions.
Received 3 September 1998 and Received in final form 3 November 1998 相似文献
3.
W. Kockelmann M. Hofmann O. Moze S.J. Kennedy K.H.J. Buschow 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):25-32
The element distributions and the magnetic ordering behaviour of compounds RNi10Si2 (R
=
Tb, Dy, Ho, Er, Tm) have been studied by neutron powder diffraction down to temperatures of 1.6 K. The compounds crystallize
in an ordered variant of the ThMn12 structure type in the tetragonal space group P4/nmm. An ordered 1:1 distribution of Ni and Si on sites 4d and 4e, respectively,
corresponds to a modulation vector [0, 0, 1] with respect to the space group I4/mmm of the ThMn12 structure. TbNi10Si2 orders antiferromagnetically below T
N
= 4.5 K with a magnetic propagation vector of [0, 0, 1/2]. The magnetic Tb moments, 8.97(2) /Tb atom at 1.6 K, are aligned along the c-axis. The Ni sites in TbNi10Si2 do not carry any ordered magnetic moments. The compounds with R
=
Dy, Ho, Er, and Tm are paramagnetic down to 1.6 K and 3.0 K, respectively.
Received 10 July 2002 / Received in final form 12 September 2002 Published online 29 October 2002 相似文献
4.
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
5.
H.A. Radovan H.H. Wen P. Ziemann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(4):533-540
Using a specially designed SQUID magnetometer we measured the temperature dependence of the critical current density in a
ring patterned thin film for magnetic fields parallel to the c-axis. In addition, the temporal relaxation of the remanent state as prepared by field cooling in an external field of 100
Oe at different temperatures is determined. The j
c
(
T
) data show a field-dependent anomalous kink close to Tc pointing to reduced dissipation with increasing temperature allowing to construct a corresponding H-T borderline. A similar behavior is observed for the normalized relaxation rate S
(
T
) as extracted from the temporal behavior of the remanent state, which, at low temperatures, exhibits the expected increase
for increasing T-values, while an anomalous decrease of S
(
T
) is found for temperatures above 85 K. While the low-T regime is attributed to creep of 2D pinned single vortex lines, the high-T behavior is suggested to be dominated by collective motion with a more sluggish dynamics. This change in dynamics is also
reflected by the activation barriers for flux creep U
(
j
), which show a corresponding crossover in μ from 0.06 to 0.99. An additional scaling analysis of the E-j characteristics for according to vortex glass theory reveals quasi-2D collective creep behavior with .
Received: 8 April 1998 / Revised: 15 July 1998 / Accepted: 2 September 1998 相似文献
6.
B. Gorshunov C.A. Kuntscher P. Haas M. Dressel F.P. Mena A.B. Kuz'menko D. van der Marel T. Muranaka J. Akimitsu 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(2):159-161
Far-infrared reflectivity studies on the polycrystalline intermetallic compound MgB2 with a superconducting transition temperature T
c
= 39 K were performed at temperatures 20 K to 300 K. We observe a significant raise of the superconducting-to-normal state reflectivity
ratio below 70
cm
-1
, with a maximum at about 25-30
cm
-1
, which gives a lower estimate of the superconducting gap of 2Δ(0)
≈ 3-4 meV.
Received 7 March 2001 and Received in final form 18 April 2001 相似文献
7.
J. Dec W. Kleemann Th. Woike R. Pankrath 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):627-632
The complex dielectric susceptibility of Sr
0.61
Ba
0.39
Nb
2
O
6
:Ce
3+
(SBN61:Ce) has been measured at frequencies and temperatures before and after poling. The relaxor behaviour with large polydispersivity observed above the ferroelectric phase transition
temperature, T
c
= 360 and 340 K for x
(Ce) = 0 and 0.0066, respectively, is perfectly modeled within the framework of Chamberlin's dynamically correlated domain approach.
Below T
c
the dynamic nanodomain state crosses over into a ferroelectric state with polydispersive domain wall dynamics at very low
frequencies. Presumably SBN61:Ce belongs to the three-dimensional random field Ising rather than to the dipole glass universality
class.
Received 1 October 1999 相似文献
8.
J. Souletie Y. Tabata T. Taniguchi Y. Miyako 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):43-46
The usual scaling equations at a phase transition, employed out of their usual validity range, with Tc a negative constant, fit properties observed in correlated electron systems with unmatched accuracy. We illustrate this behavior
with our data in Ce(Ru1-xRhx)2Si2 for x
= 0.4 and 0.5 and comment these results and what they imply physically.
Received 22 June 1998 and Received in final form 29 September 1998 相似文献
9.
M. Hervieu A. Barnabé C. Martin A. Maignan F. Damay B. Raveau 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):31-41
Charge ordering phenomena in the manganites Ca1-xSmxMnO3 have been studied for , using electron diffraction and lattice imaging, completed by magnetic and transport measurements. Three domains can be distinguished,
depending on the nature of the structural transitions with temperature. For , the structural transition from a pseudo-tetragonal to a monoclinic form, with decreasing temperature, coincides with the
competition between ferromagnetism and antiferromagnetism that is characterized by the temperature Tpeak on the M
(
T
) curves; short-range charge ordering is observed for manganites. For the second domain, , a structural transition from an orthorhombic to a long-range charge ordered state is clearly observed with decreasing temperature.
The corresponding temperature TCO coincides with the temperature Tpeak deduced from magnetic measurements. This long range charge ordering, which appears along a, is either commensurate or incommensurate depending on the x value, with a modulation vector, q being close to x. These modulated superstructures correspond to a stacking of single Mn3+ stripes with multiple Mn4+ stripes along a, either in a commensurate or in an incommensurate manner. The third domain , is characterized by a transition to a charge ordered state with commensurate superstructure at low temperature. The latter
can be described as a “partially” charge ordered state in which single “Mn3+” stripes alternate with mixed “Mn3+/Mn4+” stripes.
Received 17 June 1998 相似文献
10.
11.
E. Chappel M.D. Núñez-Regueiro F. Dupont G. Chouteau C. Darie A. Sulpice 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):609-614
Magnetisation measurements up to 23 T and submillimeter wave ESR in the frequency region 48-380 GHz have been performed on
NaNiO2 powders at low temperature. Also typical spectra above the Néel temperature are shown. At 4 K the magnetisation shows a spin-flop transition at 1.8 T and saturation at 10 T. /Ni confirms the low spin state of the Ni3+ ions. The susceptibility exhibits a maximum at K with and K. NaNiO2 is an A-type antiferromagnet: we derive K and K for the interactions between Ni ions within and between adjacent layers, respectively. The AFMR spectra yield an energy
gap of 52.5 GHz, in agreement with the spin-flop value derived from the magnetisation. The anisotropy of the g factor observed at 100 K with can be attributed to the Jahn-Teller effect for Ni3+ ions in the low spin state, which stabilises the occupation. We finally comment on the isomorphic controversial Li1-xNi1+xO2 compound.
Received 9 March 2000 and Received in final form 13 July 2000. 相似文献
12.
Y. Kohori Y. Yamato Y. Iwamoto T. Kohara 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(4):601-604
We have carried out 115In nuclear quadrupole resonance (NQR) measurements in CeRhIn5. At ambient pressure, CeRhIn5 undergoes an antiferromagnetic AF phase transition at K. The 115In NQR spectrum has shown the appearance of a small internal field in the direction perpendicular to the tetragonal c-axis. With application of a hydrostatic pressure, the AF state is suppressed and the superconductivity appears just above
the critical pressure (P
= 17 kbar). The nuclear spin lattice relaxation rate 1/T1 of 115In measured at P
= 27 kbar indicates the occurrence of the superconductivity in the nearly AF region. In the superconducting state, 1/T1 has no Hebel-Slichter coherence peak just below of 2 K and has a power law T-dependence (T3) down to 300 mK. This is consistent with anisotropic superconductivity, with line nodes in the superconducting energy gap:
non-s-wave superconductivity occurs in CeRhIn5.
Received 5 July 2000 相似文献
13.
E. García-Matres J.L Martínez J. Rodríguez-Carvajal 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(1):59-70
A neutron diffraction study, as a function of temperature, of the title compounds is presented. The whole family (space group
Immm, a
≈ 3.8?, b
≈ 5.8?, c
≈ 11.3?) is structurally characterised by the presence of flattened NiO6 octahedra that form chains along the a-axis, giving rise to a strong Ni-O-Ni antiferromagnetic interaction. Whereas for Y-compound only strong 1D correlations exist
above 1.5 K, presenting the Haldane gap characteristic of 1D AF chain with integer spin, 3D AF ordering is established simultaneously
for both R and Ni sublattices at temperatures depending on the rare earth size and magnetic moment. The magnetic structures
of R2BaNiO5 ( R
=
Nd, Tb, Dy, Ho, Er and Tm) have been determined and refined as a function of temperature. The whole family orders with a magnetic
structure characterised by the temperature-independent propagation vector
= (1/2, 0, 1/2). At 1.5 K the directions of the magnetic moments differ because of the different anisotropy of the rare earth ions. Except
for Tm and Yb (which does not order above 1.5 K), the magnetic moment of the R3+ cations are close to the free-ion value. The magnetic moment of Ni2+ is around 1.4
, the strong reduction with respect to the free-ion value is probably due to a combination of low-dimensional quantum effects
and covalency. The thermal evolution of the magnetic structures from T
N
down to 1.5 K is studied in detail. A smooth re-orientation, governed by the magnetic anisotropy of R3+, seems to occur below and very close to T
N
in some of these compounds: the Ni moment rotates from nearly parallel to the a-axis toward the c-axis following the R moments. We demonstrate that for setting up the 3D magnetic ordering the R-R exchange interactions cannot
be neglected.
Received 19 July 2001 相似文献
14.
J. Campos-Martínez E. Carmona-Novillo J. Echave M.I. Hernández R. Hernández-Lamoneda J. Palma 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(2):159-168
A reduced dimensionality model is used to study the reaction OO
O
3
(
X1A1
) + O(
3
P
) by means of time-dependent and time-independent quantum-mechanical methods. State-selected probabilities and rate constants
are obtained for the reactive process as well as for the inelastic collision in which the vibrationally excited oxygen loses
one or more quanta. It is found that the experimentally observed jump in depletion rates above a critical value of v could be partially explained by the vibrational relaxation rather than reaction. Reaction only becomes important for relatively
high translational energies and therefore the calculated rates are too small at the temperatures of interest. It is concluded,
however, that the reaction saddle point region in the potential energy surface plays a crucial role in the enhancement of
vibrational relaxation.
Received: 3 February 1998 / Revised: 27 March 1998 / Accepted: 15 May
1998 相似文献
15.
A. Podlesnyak Th. Strässle A. Mirmelstein A. Pirogov R. Sadykov 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(4):547-552
Neutron powder diffraction was employed to study the pressure effect on the magnetic transition in the pseudobinary Laves-phase
compound Er0.57Y0.43Co2 and to determine the magnetic moments of the Er- and Co-subsystems. Our studies reveal that the onset of long-range magnetic
order for both the localized 4
f (Er) and itinerant 3
d (Co) electron moments appears at about the same temperature at ambient pressure. The pressure effect on Tc is found to be negative and equal for both sublattices, namely
T
c
/
p
∼ - 0.4 K/kbar. The values of the magnetic moments of the Er and the Co ions are found
= 5.40±0.15μ
B
/atom,
= 0.50±0.07μ
B
/atom and 5.35±0.15μ
B
/atom, 0.37±0.09μ
B
/atom, for p
= 0 and 6 kbar, respectively. Our experimental results give evidence for short-range magnetic order formation at temperatures
already above Tc and for a coexistence short- and long-range order below Tc down to 4 K.
Received 20 December 2001 / Received in final form 12 June 2002 Published online 31 October 2002
RID="a"
ID="a"e-mail: andrew.podlesnyak@psi.ch 相似文献
16.
P. Lehnen W. Kleemann Th. Woike R. Pankrath 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):633-637
The linear birefringence (LB) of Sr
0.61-x
Ba
0.39
Nb
2
O
6
:Ce
3+
x (SBN61:Ce) has been measured as a function of temperature within the range of . Large tails have been observed above the ferroelectric phase transition temperatures T
c
= 350, 328, 320 and 291 K for the concentrations x
= 0, 0.0066, 0.0113 and 0.0207, respectively. Within an Ornstein-Zernike analysis the critical exponents , and are determined. It suggests that pure SBN61 belongs to the 3D Ising universality class. Doping with Ce
3+
ions, which seem to act as random fields, enhances the relaxor properties. The critical exponents and of SBN61:Ce shift against those of the three-dimensional random-field Ising model.
Received 1 October 1999 相似文献
17.
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
18.
19.
K. Sparta G.J. Redhammer P. Roussel G. Heger G. Roth P. Lemmens A. Ionescu M. Grove G. Güntherodt F. Hüning H. Lueken H. Kageyama K. Onizuka Y. Ueda 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(4):507-516
A displacive, 2nd order structural phase transition at T
s
= 395 K from space group I
2 m below T
s
to I 4/m c m above T
s
has been discovered in the two-dimensional spin dimer compound SrCu2(BO3)2. The temperature evolution of the structure in both phases has been studied by X-ray diffraction and Raman scattering, supplemented
by differential scanning calorimetry and SQUID magnetometry. The implications of this transition and of the observed phonon
anomalies in Raman scattering for spin-phonon and interlayer coupling in this quantum spin system will be discussed.
Received 24 July 2000 and Received in final form 2 November 2000 相似文献
20.
D. Ashkenasi S. Kröger H.-D. Kronfeldt 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(2):197-205
The isotope shift (IS) and hyperfine structure (hfs) of nine levels (31720 to 38921 cm-1) assigned to the configuration 4
f
12
6
s
7
s in neutral erbium have been determined experimentally using Doppler-reduced saturation absorption spectroscopy in a gas discharge.
We performed a fine structure analysis in the SL-coupling scheme of the single configuration 4
f
12
6
s
7
s, confirming and extending the classification of even parity Er I levels. We discriminated the different hfs contributions
of the 4f12 core and the (6
s
+7
s) outer electrons of the shell in a non-relativistic JJ-coupling approach and in the relativistic effective tensor operator formalism in SL-coupling. The relativistic one-electron parameters of the hfs for 167Er were fitted to the experimental data by a least squares fit procedure: [0pt] a
01
4f
=-147(3) MHz, [0pt] a
10
6s
+
a
10
7s
=-1840(30) MHz, [0pt] b
02
4f
=6560(80) MHz. The level dependencies of the isotope shift were evaluated based on crossed second order (CSO) effects. We obtained
the following results for the CSO parameters for the isotope pairs 170-168Er: d
6s7s
=-740(30) MHz, z
4f
= 0(5) MHz, (
g
3,6s
(
f
, 6
s
)+
g
3, 7s
(
f
, 7
s
))= -24(15) MHz and for 170-166Er: d
6s7s
=-1500(50) MHz, z
4f
=0(10) MHz, (
g
3,6s
(
f
,6
s
)+
g
3,7s
(
f
+7
s
))=-50(29) MHz. The resulting parameters for the hfs are compared with those known for other configurations of the Er atom and ion.
Received 16 May 1999 and Received in final form 31 January 2000 相似文献