共查询到20条相似文献,搜索用时 11 毫秒
1.
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
2.
N. El Khayati R. Cherkaoui El Moursli J. Rodríguez-Carvajal G. André N. Blanchard F. Bourée G. Collin T. Roisnel 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(4):429-442
We have studied in detail the crystal and magnetic structures of the oxyphosphates MFePO5 (M: divalent transition metal) using neutron powder diffraction as a function of temperature. All of them are isomorphic
to the mixed valence compound α-Fe2PO5 with space-group Pnma. No disorder exists between the two metallic sites. The M2+O6 octahedra share edges between them and faces with Fe3+O6 octahedra building zigzag chains running parallel to the b-axis that are connected by PO4 tetrahedra. The topology of this structure gives rise to a complex pattern of super-exchange interactions responsible of
the observed antiferromagnetic order. The magnetic structures are all collinear with the spin directed along the b-axis except for M = Co. The experimental magnetic moments of Cu+2 and Ni2+ correspond to the expected ionic value, on the contrary the magnetic moment of Fe3+ is reduced, probably due to covalence effects, and that of Co2+ is greater than the spin-only value indicating a non negligible orbital contribution. Using numerical calculations we have
established a magnetic phase diagram adapted for this type of crystal structure and determined the constraints to be satisfied
by the values of the exchange interactions in order to obtain the observed magnetic structure as the ground state.
Received 15 December 2000 and Received in final form 25 June 2001 相似文献
3.
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
4.
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
5.
M. Reehuis C. Ulrich P. Pattison M. Miyasaka Y. Tokura B. Keimer 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(1):27-34
The crystal structure and the magnetic ordering pattern of the electrically insulating perovskite CeVO3 was investigated by high-resolution powder X-ray diffraction and single-crystal neutron diffraction. A structural phase transition
from an orthorhombic to a monoclinic structure (with space groups Pbnm and P21/b, respectively) was observed upon cooling below T
s = 136 K. This transition is associated with a strong distortion of the VO6-octahedra and can be attributed to orbital ordering. A magnetic ordering transition driven by exchange interactions between
vanadium moments is observed at T
N = 124 K, and antiferromagnetic interactions between magnetic moments on vanadium and cerium ions induce a progressive magnetic
polarization of the cerium sublattice at lower temperatures. The full magnetic structure is described by a superposition of
the modes (C
x
, F
y
, −) and (F
x
, C
y
, −). The unit cell volume and the tilt angles of the VO6-octahedra in the CeVO3-crystal structure are anomalous compared to those of other members of the series RVO3 (R = lanthanide atom), and the ordered magnetic moments on both vanadium and cerium sublattices at low temperatures are considerably
smaller than the free-ion values of V3+ and Ce3+. Possible origins of this behavior are discussed. 相似文献
6.
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
7.
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
8.
J. Blasco J. García M.C. Sánchez J. Campo G. Subías J. Pérez-Cacho 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):469-479
Magnetic measurements have been carried out in different LaNi1-xMnxO
3 + δ
samples with 0.1 ⩽
x
⩽ 0.9. All these samples show two magnetic anomalies, one at relatively high temperature characteristic of a ferromagnetic ordering
and the other at low temperature, typical of magnetic relaxation phenomena. Neutron diffraction patterns indicate that long-range
ferromagnetic ordering is only achieved for x
≥ 0.5. Neutron patterns of LaNi0.5Mn0.5O
3 + δ
samples show an ordered arrangement of Ni and Mn atoms in the perovskite lattice. LaNi0.5Mn0.5O
3 + δ
is then, a double perovskite A2BB'O6 whereas Ni and Mn atoms are randomly distributed for the rest of the samples. X-ray magnetic circular dichroism experiments
confirm the presence of collinear ferromagnetism in LaNi0.5Mn0.5O
3 + δ
. The role of competitive magnetic interactions, structural disorder, magnetic anisotropy and magnetic disaccommodation is
also discussed
Received 19 July 2002 / Received in final form 23 October 2002 Published online 31 December 2002 相似文献
9.
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
10.
K. Proke? J. A. Mydosh 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(1):1-6
We have studied the unusual low-temperature magnetic phase of Er2Ni2Pb using powder neutron diffraction measurements in zero field down to 460 mK. Our previous neutron diffraction experiments
down to 1.5 K showed that magnetic Bragg reflections seen in Er2Ni2Pb can be indexed by several propagation vectors that partially coexist. All the incommensurate propagation vectors seemed
to disappear in the low temperature limit. The present study, however, shows that reflections belonging to the propagation
vector q’ = (0.47 0 1/2) do not disappear but remain present down to 460 mK. This highly unexpected result suggests that the magnetic
structure described by this propagation vector might not be a simple sine-wave modulation. One interesting possibility here
is a spin-slip structure as the ground state. 相似文献
11.
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
12.
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
13.
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
14.
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
15.
A. Garnier D. Gignoux B. Ouladdiaf D. Schmitt T. Shigeoka 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):423-427
Single crystal magnetization measurements and powder neutron diffraction on tetragonal ErRu2Ge2 as well as anisotropy of the paramagnetic susceptibility and specific heat measurements on ErRu2Si2 are presented. Besides the huge crystal field contribution to the uniaxial anisotropy, which favors the basal plane, a strong
in-plane anisotropy is evidenced. From these features and neutron diffraction experiments it is shown that magnetic structures
of these materials are double-Q and accordingly non-colinear below their Néel temperature (5.2 and 6.0 K for Ge and Si based compounds, respectively). The
magnetic structures induced during the metamagnetic processes are discussed.
Received 24 December 1999 相似文献
16.
Summary M?ssbauer measurements have been made on two kinds of spin-glass (SG) systems: one is the magnetically non-diluted mixed compound
Fe0.5Mn0.5TiO3 with the SG-freezing temperatureT
SG=21.5K, and the other is the diluted one Fe0.2Mg0.8TiO3 withT
SG=6K. We have shown that the temperature variation of the M?ssbauer spectrum of Fe0.2Mg0.8TiO3 above and around itsT
SG is essentially different from that of Fe0.5Mn0.5TiO3: the former is typical of a cluster-glass and the latter of an ordinary spin-glass. The present work has clearly demonstrated
that the M?ssbauer spectroscopy is the most useful and unique technique to distinguish a cluster-glass from an ordinary spin-glass.
Paper presented at the ICAME-95, Rimini, 10–16 September 1995 相似文献
17.
S. Hébert A. Maignan V. Hardy C. Martin M. Hervieu B. Raveau R. Mahendiran P. Schiffer 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(3):419-424
The low temperature magnetic and transport properties of the Pr0.5Ca0.5Mn1-xNixO3 manganites ( 0≤
x
≤0.1) have been investigated. The presence of Ni hinders the charge and orbital ordering observed in Pr0.5Ca0.5MnO3 and favors the creation of ferromagnetic regions, leading to phase separation. The ferromagnetic fractions induced by the
Ni substitution have been estimated from magnetization measurements, they are large and reach 40% for 4% of Ni. Steps are
observed in the M
(
H
) and ρ(
H
) curves of all the samples at T
< 5 K. They are similar to the steps observed in Pr0.5Ca0.5Mn1-xMxO3, where M is a non magnetic cation (Mg2+, Ga3+,...), and for which the ferromagnetic fractions are very small (less than 2%), however, their appearance is restricted to
lower temperatures (T
< 5 K) with Ni dopant than with non magnetic cations. This study shows that steps can be observed in a wide range of phase-separated
systems, even when the ferromagnetic fraction is very large.
Received 5 April 2002 / Received in final form 8 July 2002 Published online 14 October 2002
RID="a"
ID="a"e-mail: antoine.maignan@ismra.fr 相似文献
18.
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
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.
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