共查询到20条相似文献,搜索用时 31 毫秒
1.
E. Rastelli A. Tassi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(3):341-347
Ferromagnetic spin chains of a hexagonal lattice coupled by a weak antiferromagnetic interaction J1 develop a helix arrangement if the intrachain antiferromagnetic NNN exchange J2 is sufficiently large. We show that the classical minimum energy spin configuration is an umbrella when an external magnetic field is applied. The scenario is dramatically changed by quantum fluctuations. Indeed we find
that the zero point motion forces the spins in a plane containing the magnetic field so that classical expectation is deceptive
for our model. Our result is obtained by controlled expansion in the low field-long wavelength modulation limit.
Received: 9 September 1997 / Revised: 15 October 1997 / Accepted: 17 November 1997 相似文献
2.
P. Politi M.G. Pini 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(4):475-481
We study the effect of dipolar interactions on a magnetic striped monolayer with a microscopic unit cell of square symmetry,
and of size spins. Even if the aspect ratio r=N
x
/N
y
is very large, an in-plane shape anisotropy is always negligible, except if Ny is fairly small (N
y
<40). In-plane domains are not possible, except for values of the dipolar coupling larger than the domain wall energy.
Received: 11 July 1997 / Revised: 24 September 1997 / Accepted: 24 October 1997 相似文献
3.
M. Georgelin A. Pocheau 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):169-174
The polycrystalline perovskitelike manganese oxides La1-xAxMnO (A = Na, and K, ) have been fabricated by sol-gel technique. For all the compositions explored in this work, the average manganese oxidation
state is practically constant, at for A = Na, and for A = K, respectively. A close relationship is confirmed to hold between the Curie temperature (Tc) and the bond distance of Mn-O. Results of magnetic measurements show that these materials can be utilized as suitable candidates
for magnetic refrigerants with wide applied temperature span, for their significant entropy change and the easily tuned Curie
temperature.
Received: 12 September 1997 / Revised: 18 December 1997 / Accepted: 21 January 1998 相似文献
4.
In the past different models for the magnetic salt vanadyl pyrophosphate (VO)2P2O7 were discussed. Neither a spin ladder nor an alternating chain are capable to describe recently measured magnetic excitations.
In this paper we propose a 2D model that fits better to experimental observations.
Received: 29 May 1998 / Received in final form: 25 September 1998 / Accepted: 30 September 1998 相似文献
5.
Y.M. Yarmoshenko M.I. Katsnelson E.I. Shreder E.Z. Kurmaev A. Slebarski S. Plogmann T. Schlathölter J. Braun M. Neumann 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(1):1-3
The XPS MnL-spectra of Co2MnSn, a nearly half-metallic ferromagnet (HMF) and Pd2MnSn were investigated. The most drastical feature of the spectra observed is the well-defined magnetic splitting of the Mn
2p
3/2
, 2p
1/2
lines. This gives direct evidence of the existence of well-defined local magnetic moments in Heusler alloys in comparison
with other itinerant-electron ferromagnets. The calculations of Mn2p XPS spectra of these materials were carried out using
a fully relativistic generalization of the one-step model of photoemission and show excellent agreement with experiment.
Received: 31 October 1997 / Received in final form: 28 November 1997 / Accepted: 18 December 1997 相似文献
6.
Y. Duan M. Jungen 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(2):183-190
Density functional self-consistent spin-polarized calculations with the Discrete Variational Method were performed to obtain
the electronic structures of cadmium chalcogenide beryllosilicate sodalites Cd8[BeSiO4]6Z2 and their bulk materials CdZ (Z = S, Se, Te). Similar as their bulk materials, these sodalites are also semiconductors. From
their density of states and charge distributions, it was found that there is greater localization of the electron density
in the sodalites compared with that of the bulk. The band gaps in their bulk compounds are different from those in the sodalite
structures due to the electrons of Si, Be and O filled in. Different from their bulk materials, the d electrons of Cd play
an important role to form an unseparated valence band with all orbitals of other elements. The calculated magnetic moments
of these three materials are very small since all d atomic orbitals are fully occupied.
Received: 28 March 1997 / Revised: 18 July 1997 / Accepted: 9
September 1997 相似文献
7.
Z.-Q. Jin W. Tang J.-R. Zhang H.-X. Qin Y.-W. Du 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(1):41-44
The intermetallic compound Nd-Fe-Ti-N has been successfully synthesized by a mechanical alloying process. The structure and
magnetic properties of the sample have been studied using X-ray diffraction and magnetic measurements. It is found that alloy exhibits a nanocrystalline ThMn12-type tetragonal structure with lattice parameters of a=0.8723 nm and c=0.4896 nm. The saturation magnetization MS and effective magnetic anisotropy Keff of the compound have been determined by investigating magnetization processes. The calculated results based on the law of
approach to magnetic saturation have been successfully used to determine the constant Keff. The difference between observed and calculated values in magnetization is lower than 3%. Of all terms in the law of approach
to saturation, it is the 1/H
2
term, which is attributed more to non-compensated anisotropy energy, that has the prevailing effect for the compound. The
absorption of nitrogen is found to increase unit cell volume, MS and Keff.
Received: 28 October 1996 / Revised: 14 March 1997 and 4 August 1997 / Accepted: 8 August 1997 相似文献
8.
M. Stenger S. Baumhoff J.-Y. Prieur J. Joffrin J.-P. Contour 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(2):177-182
We present measurements of the attenuation and phase velocity of surface acoustic waves in thin YBa2Cu3O films as a function of temperature, in magnetic fields up to 3.6 T applied parallel to the c-axis of the films. We have observed anomalies in both, the attenuation and the phase velocity in the vicinity of the superconducting
critical temperature which do not depend on the magnetic field. Possible origins of these anomalies, observed, to our knowledge,
for the first time in YBa2Cu3O thin films, are discussed and compared to bulk acoustic wave experiments. We present a kind of feedback technique for surface
acoustic waves which improves the sensitivity of this type of measurement. The actual sensitivity limits are mentioned.
Received: 7 August 1997 / Revised: 7 November 1997 / Accepted: 17 November 1997 相似文献
9.
R. Guirado-López D. Spanjaard M.-C. Desjonquères A.M. Oleś 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):437-446
We analyze the stability of magnetic states obtained within the tight-binding model for cubooctahedral (Oh) and icosahedral (Ih) clusters of early 4d (Y, Zr, Nb, Mo, and Tc) transition metals. Several metastable magnetic clusters are identified which suggests the existence
of multiple magnetic solutions in realistic systems. A bulk-like parabolic behavior is observed for the binding energy of
Oh and Ih clusters as a function of the atomic number along the 4
d-series. The charge transfer on the central atom changes sign, while the average magnetic moments present an oscillatory behavior
as a function of the number of d electrons in the cluster. Our results are in agreement with other theoretical calculations.
Received: 20 November 1997 / Received in final form: 9 March 1998 / Accepted: 30 March 1998 相似文献
10.
D. Augier D. Poilblanc 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(1):19-28
Properties of low-dimensional spin-Peierls systems are described by using a one-dimensional S
=1/2 antiferromagnetic Heisenberg chain linearly coupled to a single phonon mode of wave vector (whose contribution is expected to be dominant). By exact diagonalizations of small rings with up to 24 sites supplemented by a finite size scaling analysis, static and dynamical properties are investigated. Numerical evidences
are given for a spontaneous discrete symmetry breaking towards a spin gapped phase with a frozen lattice dimerization. Special
emphasis is put on the comparative study of the two inorganic spin-Peierls compounds CuGeO3 and NaV2O5 and the model parameters are determined from a fit of the experimental spin gaps. We predict that the spin-phonon coupling
is 2 or 3 times larger in NaV2O5 than in CuGeO3. Inelastic neutron scattering spectra are calculated and similar results are found in the single phonon mode approximation
and in the model including a static dimerization. In particular, the magnon S
=1 branch is clearly separated from the continuum of triplet excitations by a finite gap.
Received: 30 July 1997 / Revised: 16 September 1997 / Accepted: 10 October 1997 相似文献
11.
D. Elefant G. Reiss C. Baier 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(1):45-53
On bulk layered single crystals (Bi0.25Sb0.75)2Te3 with a hole concentration cm-3 and a mobility cm2/Vs magnetoresistance and Hall effect investigations were performed in the temperature range T = 1.4 K ... 20 K in magnetic fields up to 18 T. For the magnetic field perpendicular to the layered structure giant Shubnikov-de
Haas oscillations are measured; the positions of the maxima are triplets in the reciprocally scaled magnetic field. From the
damping of the amplitudes with increasing temperature the cyclotron mass m
c
= 0.12m
0
is evaluated. Correlated with the SdH oscillations doublets of Hall effect plateaus (or kinks in low fields) are found. The
weak well known Shubnikov-de Haas oscillations from the generally accepted multivallied highest valence band can be detected
as a modulation on the giant oscillation. The high anisotropy of the SdH oscillations and their triplet structure in connection
with the layered crystal structure lead us to suggest that the effects are caused by hole carrier pairing (mediated by the
bipolaron mechanism) in quasi 2D sheets parallel to the crystal layer stacks. The measured Hall plateau resistances coincide
with the quantum Hall effect values considering the number of layer stacks and the valley degeneracy of the 3D hole carrier
reservoir. The ratio of spin splitting to Landau (cyclotron) splitting is observed to be .
Received: 12 September 1997 / Revised: 8 January 1998 / Accepted: 22 January 1998 相似文献
12.
A.V. Prokofiev F. Büllesfeld W. Assmus H. Schwenk D. Wichert U. Löw B. Lüthi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):313-316
Experimental results on magnetic resonance (ESR) and magnetic susceptibility are given for single crystalline (VO)2P2O7. The crystal growth procedure is briefly discussed. The susceptibility is interpreted numerically using a model with alternating
spin chains. We determine J
=51 K and . Furthermore we find a spin gap of meV from our ESR measurements. Using elastic constants no indication of a phase transition forcing the dimerization is seen
below 300 K.
Received: 22 December 1997 / Accepted: 17 March 1998 相似文献
13.
N.J. Poirot P. Simon P. Odier J.M. Bassat 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(4):469-474
We report an investigation of magnetic resonance by ESR in oxygen-doped La2NiO emphasizing extensively for the first time the role of oxygen stoichiometry. The work is performed at room temperature and
on powders with . At low field an hysteresis is detected between increasing and decreasing fields, it depends upon . The resonance lines have characteristic features of ferromagnetic resonance. The intensity () is used as an experimental parameter for investigating the effect of . It allows to built a diagram closely connected to the phase diagram . It suggests a ferromagnetic coupling depending upon . When the (average) structure is tetragonal the low intensity is due to a magnetic polaron of low resistivity. In ranges
where a phase separation is detected, the ferromagnetic coupling has a structural origin (DM or local anisotropy) with apparently
a strong influence on the electrical resistivity.
Received: 3 November 1997 / Accepted: 23 December 1997 相似文献
14.
A phenomenological model is presented to describe weakly charged polymer gels based on the classical elasticity theory. The
structure factor of the gel is calculated considering both thermal and frozen concentration fluctuations as well as the screened
Coulomb interaction. In agreement with the recent experimental finding the result shows anomalous crosslink-density dependence
of the scattering profiles.
Received: 28 March 1997 / Revised: 4 September 1997 / Accepted: 23 October 1997 相似文献
15.
M.L. Gardel R. Vandenbosch B.P. Henry C. Cooper D.I. Will 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(1):79-81
The destruction cross-section for 22.5 and 50 keV C1- , for 10 and 50 keV C8
1- and for 50 and 75 keV C60
1- clusters in collisions with H2 has been measured by an attenuation method. The destruction of the cluster anions is dominated by electron detachment rather
than fragmentation and is of the order of the geometric cross-section. The cross-sections vary little with bombarding energy.
Received: 16 September 1998 / Received in final form: 23 February 1999 相似文献
16.
J. Kästner J. Neuhaus E. F. Wassermann W. Petry B. Hennion H. Bach 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(1):75-81
In a previous neutron scattering study, we had observed that the TA phonon softening in L12-ordered ferromagnetic Fe72Pt28 Invar is pronounced at the zone boundary M-point and leads to an antiferrodistortive phase transition at low temperatures.
Here, we report on similar neutron scattering investigations on two ordered crystals with higher Fe content to investigate
the relation between the TA phonon softening and the martensitic transformation, which occurs in Fe-rich ordered Fe-Pt. We find that the TA phonon softening, especially at the M-point zone boundary, does not depend on the composition of the investigated crystals.
In Fe74.5Pt25.5, however, the antiferrodistortive phase transition temperature is enhanced due to tetragonal strain preceding the martensitic
transition. In Fe77Pt23 a precursor driven premartensitic phase transition is not observed. The structure of the martensite is, however, influenced
by the soft mode lattice instability of the austenite. This would explain the origin of structural details found previously
for Fe3Pt thermoelastic martensite.
Received 18 January 1999 and Received in final form 11 March 1999 相似文献
17.
A. Banerjee M.K. Harbola 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(3):265-269
Using density based perturbation theory [M.K. Harbola, A. Banerjee, Phys. Lett. A 222, 315 (1996)], we calculate the static hyperpolarizabilty for spherical atoms and ions from their ground-state densities. Since densities are being employed, calculations are performed
using approximate functionals for the kinetic and the exchange-correlation energies. Use of densities - instead of the wavefunctions
or Kohn-Sham orbitals - reduces the computational effort substantially. The results obtained are within of those calculated from the corresponding orbital-based calculations.
Received: 23 June 1997 / Revised: 25 September 1997 / Accepted: 24 December 1997 相似文献
18.
A.A. Boulbitch P. Tolédano 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):355-362
The behaviour of the antiferroelectric SmCA liquid crystal phase under applied electric field is discussed theoretically. The phase diagram involving the SmA, SmCA and SmC
A
* phases is worked out and shown to exhibit a Lifshitz critical point. The deformation of the bilayer structures induced by
the field transforms the SmCA phases into a ferrielectric phase whose specific configuration is described.
Received: 23 October 1997 / Revised: 8 April 1998 / Accepted: 14 July 1998 相似文献
19.
S. Knorr A. Grupp M. Mehring U. Kirbach A. Bartl L. Dunsch 《Applied Physics A: Materials Science & Processing》1998,66(3):257-264
82 , Y@C82, and La@C82 in frozen solutions. We were able to determine the g tensors of these molecules by analysing magnetic field spectra at X-band
(9.5 GHz) and W-band (94 GHz) frequencies. Moreover, in Y@C82 we have investigated the hyperfine interaction of the 89Y nuclear spin (I=1/2) with the electron spin on the C82 cage. The principal values of the hyperfine tensor A and the relative orientation of g and A tensors were determined by applying
three- and four-pulse electron spin echo envelope modulation techniques (ESEEM).
Received: 3 September 1997/Accepted: 10 November 1997 相似文献
20.
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