共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
D. Hupfeld W. Schweika J. Strempfer W.A. Caliebe U. Köbler K. Mattenberger G.J. McIntyre F. Yakhou Th. Brückel 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):273-289
We report on an investigation of the magnetic properties of Gd
x
Eu
1 - x
S mixed crystals with compositions in the range of 0.6 <
x
< 1. For the two samples Gd
0.8
Eu
0.2
S and Gd
0.73
Eu
0.27
S a long-range antiferromagnetic order was observed at low temperatures. Element-specific measurements exhibited a different
temperature dependence of the reduced sublattice magnetisation of the two magnetic species. A model calculation and Monte
Carlo simulations revealed that the different temperature dependence is due to frustration effects. These frustration effects
lead to a breakdown of the long-range order for higher europium contents. For the Gd
0.67
Eu
0.33
S-sample we were able to observe a short-range antiferromagnetic order with correlation lengths of a few 10? with X-ray resonance exchange scattering.
Received 25 April 2001 and Received in final form 3 December 2001 相似文献
3.
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
4.
C.M. Teodorescu F. Chevrier R. Brochier C. Richter V. Ilakovac O. Heckmann P. De Padova K. Hricovini 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):305-313
Interface reaction and magnetism of epitaxially-grown Fe on InAs(100) are studied by core-level photoemission (As 3d and In 4d) and Fe 2p X-ray magnetic circular dichroism using synchrotron radiation. The reactivity of Fe/InAs(100) is relatively low compared
to that of other interfaces involving deposition of 3d metals on III-V semiconductors. As a consequence, we observe a magnetic signal at Fe L2, 3 edges for the lowest thicknesses studied (1 ML). The atomic magnetic moment reaches a value close to that of the bulk α-Fe
(2.2 μ
B) for Fe coverages exceeding 5 ML. A ferromagnetic compound with approximate stoichiometry of FeAs is formed at the interface.
The orbital magnetism represents between 12 and 20% of the total momentum, due to 3d density of states depletion and to crystal-field modification of the electronic levels. These properties make the Fe/InAs(100)
interface very promising for spin-tunneling devices.
Received 4 April 2002 / Received in final form 13 May 2002 Published online 31 July 2002 相似文献
5.
B. Pilawa I. Keilhauer G. Fischer S. Knorr J. Rahmer A. Grupp 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):321-330
The magnetic properties of the cyclic compound [Fe6(bicine)6] LiClO4
. 2MeOH are reported. The cluster Fe6(bicine)6 forms an antiferromagnetically coupled ring structure of Fe III ions. The magnetic susceptibility is measured between 2 and 300 K and yields the exchange coupling of J/k
B = - 27.5±0.5 K. The field dependence of the magnetic moment is studied at 3 and 6 K in magnetic fields up to 5 T. The zero-field
splitting of the first excited spin states with S = 2 and 3 are determined by ESR at 94 GHz. The intra-molecular interactions of the Fe III ions are analyzed and the on-site anisotropy of the Fe III due to the ligand-configuration is determined to d /k
B = - 0.633±0.008K.
Received 28 October 2002 / Received in final form 22 February 2003 Published online 20 June 2003
RID="a"
ID="a"e-mail: bernd@piobelix.physik.uni-karlsruhe.de 相似文献
6.
J. Schnack H.-J. Schmidt J. Richter J. Schulenburg 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):475-481
For many spin systems with constant isotropic antiferromagnetic next-neighbour Heisenberg coupling the minimal energies E
min(S) form a rotational band, i.e. depend approximately quadratically on the total spin quantum number S, a property which is also known as Landé interval rule. However, we find that for certain coupling topologies, including
recently synthesised icosidodecahedral structures this rule is violated for high total spins. Instead the minimal energies
are a linear function of total spin. This anomaly results in a corresponding jump of the magnetisation curve which otherwise
would be a regular staircase.
Received 27 August 2001 and Received in final form 18 October 2001 相似文献
7.
P. Bonville J.A. Hodges M. Shirakawa M. Kasaya D. Schmitt 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):349-355
Orthorhombic EuPdSb is known to undergo two magnetic transitions, at 12 K and at T
N≃ 18 K, and in phase III (T < 12 K), single crystal magnetisation data have shown that the spin structure is collinear antiferromagnetic, with magnetic
moments along the crystal a axis. From a 151Eu M?ssbauer absorption study, we show that, at any temperature within phase III, all the moments have equal sizes, and that
in phase II (12 K< T <18 K) the magnetic structure is modulated and incommensurate with the lattice spacings. The modulation is close to a pure
sine-wave just below T
N = 18 K, and it squares up as temperature is lowered. We measured the thermal variations of the first and third harmonics
of the moment modulation, and we could determine the first and third harmonics of the exchange coupling. We furthermore show
that the antiferromagnetic-incommensurate transition at 12 K is strongly first order, with a hysteresis of 0.05 K, and that
the incommensurate-paramagnetic transition at 18 K is weakly first order. Finally, we present an explanation of the spin-flop
transition observed in the single crystal magnetisation data in phase III when || in terms of an anisotropic molecular field tensor.
Received 17 January 2001 and Received in final form 20 March 2001 相似文献
8.
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
9.
Large resonant magnetization-sensitive X-ray scattering is predicted to occur in the vicinity of the LII, LIII, MII-MV absorption edges in the rare earth and actinide elements, and at the LII, LIII edges in the transition and 4d elements. Additional longer wavelength resonances will occur in the actinides and 4d elements.
These “magnetic” resonances result from electric multipole transitions, with the sensivity to the magnetization arising from
exchange and spin-orbit correlations. For some transitions, the magnetic scattering will be comparable to the charge scattering. 相似文献
10.
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
11.
O. Zaharko A. Cervellino H.-Ch. Mertins H. Grimmer F. Schäfers D. Arvanitis 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(4):441-448
Magnetic circular dichroism (MCD) in X-ray absorption has been measured at the L
2, 3
edges of Fe in ex-situ grown Fe and Fe
0.50
Co
0.48
V
0.02
films by means of the transmission method. A new approach is developed for fitting the observed transmittance, which describes
the resonance lineshapes as (generalized) Fano profiles. Analytical integration of each single resonance allows a more reliable
determination of the orbital and spin magnetic moments based on the MCD sum rules. The results are consistent with an increase
of the Fe spin and orbital magnetic moment in Fe-Co alloys as obtained by other experiments and band structure calculations.
Received 15 August 2000 and Received in final form 11 June 2001 相似文献
12.
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
13.
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
14.
A. Marucci P. Launois R. Moret A. Pénicaud 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):29-34
The phase diagram of the newly synthesized mixed crystal C60-biphenyl is investigated as a function of temperature by single-crystal X-ray scattering. Diffuse scattering investigations
evidencing complex disorder and local order effects are presented. Two phase transitions leading to two different doublings
of the high temperature unit cell are observed, at 212 K and 147 K. The first transition is attributed to the ordering of
twisted biphenyls, which couples to the orientational ordering of the C60 molecules as the temperature decreases. Full ordering of the C60 molecules is achieved below 100 K only, in the low temperature phase. The rich phase diagram of C60-biphenyl is due to the interplay between fullerene and biphenyl ordering phenomena.
Received 31 August 2001 and Received in final form 4 December 2001 相似文献
15.
M.E. Gouvêa A.S.T. Pires 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):147-153
We use the self-consistent harmonic approximation (SCHA) to study the two-dimensional classical Heisenberg anisotropic (easy-plane)
ferromagnetic model including nearest- and next-nearest neighbor exchange interactions. For temperatures much lower than the
Kosterlitz-Thouless phase transition temperature T
KT, spin waves must be the most relevant excitations in the system and the SCHA must account for its behavior. However, for
temperatures near T
KT, we should expect vortex pairs to be quite important. The effect of these vortex excitations on the phase transition temperature
is included in our theory as a renormalization of the exchange interactions. Then, combining the SCHA theory to the renormalization
effect due to vortex pairs, we calculate the dependence of T
KT as a function of the easy-plane anisotropies and exchange interactions.
Received 3 April 2001 and Received in final form 20 September 2001 相似文献
16.
D. Maurer R. Heichele N. Lingg V. Müller A.M. Balbashov 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):425-431
The magneto-elastic properties of single-crystalline La0.95Sr0.05MnO3 have been studied ultrasonically. Our investigations focussed on the temperature interval where magnetic ordering starts
to evolve and results in a spin canted antiferromagnetic ground state. In detail the experiments revealed that the magnetic
order parameter in low-doped manganite is only weakly coupled to lattice strains. Furthermore, the anomalous temperature dependence
of the order parameter as found resembles highly that in stoichiometric LaMnO3. However, the main and most surprising finding is that external magnetic fields favor the spin canted phase in La0.95Sr0.05MnO3. It is unclear at present how the exchange interaction can be tuned by magnetic fields in the way observed and we are not
aware of existing theoretical concepts which might give a plausible explanation for the unexpected field dependent behavior
of the critical temperature. We believe, however, that this behavior primarily results from the fact that the exchange interaction
depends sensitively on the orbital configuration of the manganese d electrons.
Received 27 March 2000 相似文献
17.
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
18.
Ch. Giorgetti E. Dartyge F. Baudelet Ch. Brouder 《Applied Physics A: Materials Science & Processing》2001,73(6):703-706
X-ray Magnetic Circular Dichroism (XMCD) at LII,III edges of rare earths in rare earth–3d transition metal compounds is still a subject of study. We present experimental evidence
of electric quadrupolar transitions at LIII and LII edges of Er in the ErFe2 Laves phase. These experimental results are compared with atomic calculation taking into account crystal electric field effects
on the Er site.
Received: 30 May 2001 / Accepted: 4 July 2001 / Published online: 5 October 2001 相似文献
19.
E. Müller-Hartmann A. Reischl 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):173-183
The derivation of effective spin models describing the low energy magnetic properties of undoped CuO2-planes is reinvestigated. Our study aims at a quantitative determination of the parameters of effective spin models from those of a multi-band model and is supposed to be relevant
to the analysis of recent improved experimental data on the spin wave spectrum of La2CuO4. Starting from a conventional three-band model we determine the exchange couplings for the nearest and next-nearest neighbor
Heisenberg exchange as well as for 4- and 6-spin exchange terms via a direct perturbation expansion up to 12th (14th for the 4-spin term) order with respect to the copper-oxygen hopping tpd. Our results demonstrate that this perturbation expansion does not converge for hopping parameters of the relevant size.
Well behaved extrapolations of the couplings are derived, however, in terms of Padé approximants. In order to check the significance
of these results from the direct perturbation expansion we employ the Zhang-Rice reformulation of the three band model in
terms of hybridizing oxygen Wannier orbitals centered at copper ion sites. In the Wannier notation the perturbation expansion
is reorganized by an exact treatment of the strong site-diagonal hybridization. The perturbation expansion with respect to
the weak intersite hybridizations is calculated up to 4th order for the Heisenberg coupling and up to 6th order for the 4-spin
coupling. It shows excellent convergence and the results are in agreement with the Padé approximants of the direct expansion.
The relevance of the 4-spin coupling as the leading correction to the nearest neighbor Heisenberg model is emphasized.
Received 8 June 2001 / Received in final form 28 May 2002 Published online 19 July 2002 相似文献
20.
C. Honerkamp 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(1):81-91
We compare the one-loop renormalization group flow to strong coupling of the electronic interactions in the two-dimensional
t-t'-Hubbard model with t' = - 0.3t for band fillings smaller and larger than half-filling. Using a numerical N-patch scheme ( N = 32, ..., 96) we show that in the electron-doped case with decreasing electron density there is a rapid transition from
a d
x2 - y2-wave superconducting regime with small characteristic energy scale to an approximate nesting regime with strong antiferromagnetic
tendencies and higher energy scales. This contrasts with the hole-doped side discussed recently which exhibits a broad parameter
region where the renormalization group flow suggests a truncation of the Fermi surface at the saddle points. We compare the
quasiparticle scattering rates obtained from the renormalization group calculation which further emphasize the differences
between the two cases.
Received 19 December 2000 and Received in final form 28 February 2001 相似文献