共查询到20条相似文献,搜索用时 15 毫秒
1.
Ch. Binek T. Kato W. Kleemann O. Petracic D. Bertrand F. Bourdarot P. Burlet H. Aruga Katori K. Katsumata K. Prokes S. Welzel 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):35-40
In order to clarify the nature of the additional phase transition at H
1
(
T
) <
H
c
(
T
) of the layered antiferromagnetic (AF) insulator FeBr
2
as found by Aruga Katori et al. (1996) we measured the intensity of different Bragg-peaks in different scattering geometries. Transverse AF ordering is observed
in both AF phases, AF I and AF II. Its order parameter exhibits a peak at T
1
=
T
(
H
1
) in temperature scans and does not vanish in zero field. Possible origins of the step-like increase of the transverse ferromagnetic
ordering induced by a weak in-plane field component when entering AF I below T1 are discussed.
Received 27 September 1999 and Received in final form 6 December 1999 相似文献
2.
Y.S. Lee M. Greven B.O. Wells R.J. Birgeneau G. Shirane 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):15-22
We report a neutron scattering study of the instantaneous spin correlations in the two-dimensional spin S
=5/2 square-lattice Heisenberg antiferromagnet Rb2MnF4. The measured correlation lengths are quantitatively described, with no adjustable parameters, by high-temperature series
expansion results and by a theory based on the quantum self-consistent harmonic approximation. Conversely, we find that the
data, which cover the range from about 1 to 50 lattice constants, are outside of the regime corresponding to renormalized
classical behavior of the quantum non-linear model. In addition, we observe a crossover from Heisenberg to Ising critical behavior near the Néel temperature; this crossover
is well described by a mean-field model with no adjustable parameters.
Received: 3 March 1998 / Received in final form: 4 May 1998 /
Accepted: 19 May 1998 相似文献
3.
J. Strempfer Th. Brückel W. Caliebe A. Vernes H. Ebert W. Prandl J.R. Schneider 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):63-72
Results of high-energy magnetic X-ray diffraction on pure antiferromagnetic chromium are presented. The temperature dependence
of the propagation vector of the spin-density wave (SDW) and the strain-wave (SW) could be reproduced. The temperature dependence
of the magnetic integrated intensity could be measured in the transversally as well as in the longitudinally polarised SDW
phase. The magnetic form-factor has been determined in the transversally polarised SDW phase with five magnetic satellites.
For the first time a spin-orbit separation has been performed by comparing X-ray to neutron data. The small orbital contribution
to the magnetisation density turns out to be negligible, in agreement to our relativistic band-structure calculations. In
addition, measurements of strain-wave reflections have been undertaken, and the results complement previous studies.
Received 17 August 1998 and Received in final form 10 August 1999 相似文献
4.
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
5.
A. Sundaresan J.L. Tholence A. Maignan C. Martin M. Hervieu B. Raveau E. Suard 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(3):431-438
Neutron and electron diffraction, electrical transport and magnetic measurements have been carried out on a newly synthesized
electron doped Sr1-xCe
x
MnO3 (x = 0.1, 0.2, 0.3 and 0.4) system. For x=0.1, while cooling, it undergoes a first-order metal-insulator transition at 315 K which is associated with a structural
transition from cubic (Pm3m) to tetragonal (I4/mcm) due to Jahn-Teller ordering () which stabilizes a chain like (C-type) antiferromagnetic ground state with . The antiferromagnetic insulator state is insensitive to an applied magnetic field of 7 T. With increase of x, while the nuclear structure at room temperature for x=0.2 and 0.3 remains tetragonal, for x=0.4 it becomes orthorhombic (Imma) where the doping electrons seem to occupy mainly the d
x2-y2 symmetry. Further, the JT distortion and the antiferromagnetic interactions decrease with doping and a small negative magnetoresistance
appears for . Magnetic measurements show that the dilution of antiferromagnetic interaction results into a spin glass like behaviour at
low temperature for the samples with x=0.3 and 0.4. This behaviour is in contrast with the CMR properties of calcium based electron doped systems and hole doped
manganites. The stability of C-type antiferromagnetic ordering in the electron doped system with large A-site cationic size
may be responsible for the absence of double exchange ferromagnetism and CMR effect.
Received 10 September 1999 相似文献
6.
J.I. Espeso J. García Soldevilla J.A. Blanco J. Rodríguez Fernández J.C. Gómez Sal M.T. Fernández Díaz 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(4):625-632
The ground state of the strongly correlated electron CeNi1-xCux compounds has been investigated by means of neutron scattering experiments. Thus, magnetic diffraction was performed for
compounds showing long-range magnetic order (x
> 0.2). An evolution from a collinear ferromagnetic structure for x
=0.6 to a simple antiferromagnetic one for CeCu takes place through some more complex magnetic structures for intermediate compositions.
The magnetic moments are continuously reduced when the Ni content increases reflecting the progressive enhancement of the
Kondo screening. The large reduction found for x
=0.6 compound is discussed and the existence of a spin glass like component of the magnetic moment cannot be discarded. From the
quasielastic spectra, we have obtained the Kondo temperatures which are close to the magnetic ordering ones. The quasielastic
line-width evolves from a linear temperature dependence to a T
1/2
behaviour when approaching the non-magnetic limit. Then, this system provides an interesting example for the evolution of
unstable 4
f shell relaxation regimes when modifying the hybridisation strength.
Received 22 May 2000 相似文献
7.
V.I. Nizhankovskii A.I. Khar'kovskii A.J. Zaleski 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):761-766
Spontaneous magnetisation of (100) and (010) surfaces of single crystal MnF2 in the antiferromagnetic state has been discovered. The sign of the surface magnetisation is determined by the difference
in dielectric constants of MnF2 and ambient matter: magnetisation is directed to the substance with smaller .
Received 28 August 1998 and Received in final form 15 December 1998 相似文献
8.
F. Semadeni A. Amato B. Roessli P. Böni C. Baines T. Masuda K. Uchinokura G. Shirane 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):307-311
The temperature-concentration phase diagram of the Si-doped spin-Peierls compound CuGeO3 is investigated by means of neutron scattering and muon spin rotation spectroscopy in order to determine the microscopic
distribution of the magnetic and lattice dimerised regions as a function of doping. The analysis of the zero-field muon spectra
has confirmed the spatial inhomogeneity of the staggered magnetisation that characterises the antiferromagnetic superlattice
peaks observed with neutrons. In addition, the variation of the macroscopic order parameter with doping can be understood
by considering the evolution of the local magnetic moment as well as of the various regions contributing to the muon signal.
Received 6 September 2000 and Received in final form 29 January 2001 相似文献
9.
O. Toulemonde F. Studer A. Barnabé B. Raveau J.B. Goedkoop 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):233-240
X-ray absorption spectroscopy (XAS) and soft-X-ray magnetic circular dichroism (SXMCD) at the Mn L2,3-, Cr L2,3- and O-K edges of Sm0.5Ca0.5Mn1-xCrxO3 () bulk polycrystalline samples have been performed at T=20 K below the ferromagnetic Curie temperature. We show the existence of a magnetic sublattice on each of the probed cations.
Considering an electronically phase-separated system, results are compared with magnetization and resistivity measurements
and a tentative correlation with magnetoresistance properties on such doped compounds is discussed.
Received 7 January 2000 相似文献
10.
D. Mannix P.C. de Camargo C. Giles A.J.A. de Oliveira F. Yokaichiya C. Vettier 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):19-25
We report on X-ray magnetic diffraction studies of the spin density wave antiferromagnetism formed in the conduction electron
band of chromium. Non-resonant X-ray magnetic scattering was used to directly determine that chromium has zero orbital magnetisation.
Furthermore, the azimuthal dependence of this scattering provides unique evidence that chromium forms a linearly polarised
wave. In the vicinity of the K absorption edge, resonant X-ray magnetic scattering was observed. A consistent model of the
magnetic scattering has been derived from the resonant and non-resonant magnetic amplitudes. The enhancement of the magnetic
intensity arises primarily from dipole transitions from the core 1s level to 4p states. Quadrupole transitions to the magnetic 3d states are essentially non-existent due to their sensitivity to (and the absence of) orbital moment. This effect is predicted
from atomic considerations of the 3d5 ( = 0) transition metal ions.
Received 22 September 2000 相似文献
11.
O. Moze J.M. Cadogan Y. Janssen F.R. de Boer K.H.J. Buschow S.J. Kennedy 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(1):29-36
The magnetic structure of RFe6Ga6 intermetallic compounds with R = Y, Ho have been determined by neutron powder diffraction, 57Fe M?ssbauer spectroscopy, AC susceptibility, TGA (Thermo-Gravimetric Analysis) and magnetization measurements. Both compounds
crystallize in the tetragonal ThMn12 structure (space group I4/mmm) with the magnetic structure of YFe6Ga6 consisting of a simple ferromagnetic alignment of Fe moments in the basal plane with a Curie temperature of 475(5) K. Gallium
atoms are found to fully occupy the 8i site, with Fe and Ga atoms equally distributed over the 8j site, whilst Fe atoms fully
occupy the 8f site. The average Fe moments are 1.68(10)
and 1.46(10)
at 15 and 293 K, respectively. The average room temperature Fe magnetic moments determined by neutron diffraction are in
overall agreement with the average Fe moment deduced from M?ssbauer spectroscopy and bulk magnetization measurements on this
compound. The magnetic anisotropy of the compound HoFe6Ga6 is also planar in the temperature range 6-290 K, with Ho magnetic moments of 9.28(20)
and 2.50(20)
at 6 K and 290 K, respectively, coupled anti-ferromagnetically to the Fe sublattice and a Curie temperature of 460(10) K.
The magneto-crystalline anisotropies of both compounds are comparable at low temperatures.
Received 8 March 2001 and Received in final form 18 June 2001 相似文献
12.
K. Hagdorn D. Hohlwein J. Ihringer K. Knorr W. Prandl H. Ritter H. Schmid Th. Zeiske 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(2):243-254
Ho0.1Ca0.9MnO3 is a canted antiferromagnet with the magnetic space group Pn
'
ma
'. The magnetic structure is a superposition C
x
F
y
A
z of the three types of order allowed in Pn
'
ma
'. In the Ca-rich corner of the system Ho
1-x
Ca
x
MnO
3
the title compound has a strong magnetoelastic distortion , the highest metallic conductivity and a ferromagnetic component F
y close to the maximum in the series. Among the areas ab, bc, ca calculated from the lattice constants only ca shows a strong magnetoelastic effect below T
N
= 106
K. The x-, y-, z-spin components depend differently on the temperature. This gives rise to spin rotation which is particularly strong close
to T
N. MnO
6
octahedra have short bond lengths with a temperature independent average . They are practically regular at room temperature and show a Jahn-Teller distortion of 3.5% in the magnetically ordered state.
Above T
N we find small polaron conductivity. The presence of the Jahn-Teller distortion due to the only small abundance (10%) of Mn
3+
in the t
2g
3
e
g configuration is attributed to delocalised e
g electrons. In the magnetically ordered state the averaged magnetic moment of Mn is reduced appreciably from the paramagnetic
value due to spin disorder.
Received 21 January 1999 相似文献
13.
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
14.
N. Shannon T. Chatterji F. Ouchni P. Thalmeier 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):287-297
We construct a theory of spin wave excitations in the bilayer manganite La1.2Sr1.8Mn2O7 based on the simplest possible double-exchange model, but including leading quantum corrections to the spin wave dispersion
and damping. Comparison is made with recent inelastic neutron scattering experiments. We find that quantum effects account
for some part of the measured damping of spin waves, but cannot by themselves explain the observed softening of spin waves
at the zone boundary. Furthermore a doping dependence of the total spin wave dispersion and the optical spin wave gap is predicted.
Received 15 January 2002 Published online 6 June 2002 相似文献
15.
K. Prokes R.T. Gramsma Y. Janssen E. Brück K.H.J. Buschow F.R. de Boer 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):429-434
Neutron-diffraction experiments reveal that ErFe6Ga6 forms in the tetragonal ThMn12-type of structure (space group I4/mmm). The Fe sublattice orders ferromagnetically below K. The Er moments order antiparallel to the Fe moments which, below about 250 K, leads to a decrease of the total magnetization.
The easy magnetization direction of ErFe6Ga6 is perpendicular to the c-axis in the whole temperature range. Refinement at 2 K shows that ErFe6Ga6 orders ferrimagnetically with Er moments of 8.5 (2) and Fe moments at the 8(j) site of 1.9 (1) and at the 8(f) site of 1.7 (1) , respectively. At room temperature, ErFe6Ga6 exhibits the same type of magnetic order, however with substantially lower Er moments of 1.0 (4) and Fe moments at the 8(f) site of 1.2 (2) . The Fe moments at the 8(j) site amount to 1.9 (5) /Fe.
Received 24 November 1999 and Received in final form 27 March 2000 相似文献
16.
J. Voigt E. Kentzinger U. Rücker W. Schweika D. Wermeille W. Schmidt Th. Brückel 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(4):441-451
We have investigated the structural and magnetic properties of
Er|Tb
multilayers by different scattering methods. Diffuse X-ray scattering under
grazing incidence reveals the interface structure in
Er|Tb
bilayers and trilayers, indicating vertically correlated roughness between the Er and Tb interfaces. The magnetic properties
of
ErnEr|TbnTb
superlattices have been studied as a function of the superlattice composition (indices denote the number of atomic layers).
Coupled ferromagnetic structures exist in all investigated samples. The phase transition temperature varies with the Tb layer
thickness.
Modulated magnetic order is short range for all samples beside the
Er20|Tb5
superlattice, the sample with the smallest Tb layer thickness.
We observe dipolar antiferromagnetic coupling between single ferromagnetic Tb layers in all samples, with the onset of this
ordering depending on the Tb layer thickness. Due to competing interactions, exchange coupling is limited to the interface
near region. Therefore long range modulated magnetic order is observed in the
Er20|Tb5
superlattice only, where the interface regions overlap.
The distinct differences to the magnetic structure of an Er0.8Tb0.2
alloy film are explained by a highly anisotropic arrangement of neighbouring
atoms due to the correlated roughness. 相似文献
17.
F. Bourdarot A. Bombardi P. Burlet R. Calemczuk G.H. Lander F. Lapierre J.P. Sanchez K. Mattenberger O. Vogt 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):605-611
We report specific heat and neutron diffraction measurements of seven samples in the solid solution system UxLa1-xS. All samples have the simple fcc NaCl crystal structure. Both specific heat and neutron diffraction confirm the suggestion
from the earlier magnetic measurements that the ferromagnetism disappears abruptly at 0.57. Near there is a doubling of the electronic contribution to the specific heat, as compared to the value of 23 mJ mol-1K-2 in pure US. Around the widths of the nuclear Bragg peaks show a considerable broadening, as well as anomalies in the mean lattice parameter,
as compared to those expected from Vegard's law. A preliminary analysis suggests this broadening may be due to a loss of long
range lattice order near . However, these changes are independent of temperature, so that further experiments are necessary before they can be associated
with the changes in magnetic behavior at .
Received 18 September 1998 相似文献
18.
A.-L. Barra G. Chouteau A. Stepanov A. Rougier C. Delmas 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(4):551-562
compounds have a layered structure made of alternating Ni-O and Li-O slabs. An amount z of extra divalent Ni ions is always present in the Li-O layers. We show, using high field magnetisation, static and dynamic
susceptibility and high frequency ESR, that the magnetic properties are driven by the z parameter. The compounds can be described as ferromagnetic Ni-O layers, bridged by clusters possessing a net ferromagnetic
moment.
Received: 24 July 1998 / Revised and Accepted: 23 September 1998 相似文献
19.
S. Hébert A. Maignan R. Frésard M. Hervieu R. Retoux C. Martin B. Raveau 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(1):85-89
The doping of the manganese site by iridium (up to 15%) in the small A cation manganites Pr1-xCaxMnO3 ( 0.4 ?
x
? 0.8), has been investigated as a new method to suppress charge-ordering and induce CMR effects. Ir doping leads to ferromagnetism
and to insulator to metal transitions, with high transition temperatures reaching 180 K and CMR ratio in 7 T as large as 104. The efficiency with which iridium induces ferromagnetism and CMR is compared to previous results obtained with other substitutions
(Ru, Rh, Ni, Cr...). The ionic radius of the foreign cations and their mixed-valencies are found to be the main parameters
governing the ability to collapse the charge-ordered state.
Received 14 May 2001 and Received in final form 2 July 2001 相似文献
20.
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