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1.
Yu. N. Mitsai K. M. Skibinskii M. B. Strugatskii V. V. Tarakanov 《Physics of the Solid State》1997,39(5):803-806
A theory of magnetoacoustic birefringence in the weak, easy-plane ferromagnet FeBO3 is formulated with allowance for the mechanical boundary conditions at the sample in the experiment. The amplitude of the
acoustic wave transmitted through the crystal is calculated as a function of the magnetic field; the dependence satisfactorily
describes the experimental results.
Fiz. Tverd. Tela (St. Petersburg) 39, 901–904 (May 1997) 相似文献
2.
I. Sh. Akhmadullin S. A. Migachev M. F. Sadykov M. M. Shakirzyanov 《Physics of the Solid State》2004,46(2):312-315
An experimental study of the magnetic birefringence of sound in the α-Fe2O3 easy-plane antiferromagnet is reported. The amplitude of transverse sound transmitted through the crystal along the C3 trigonal axis was found to oscillate depending on the magnitude of the magnetic field H applied in the basal plane (H ⊥ C3). The experiments provide qualitative support for the theory of this phenomenon developed earlier by Turov. Possible reasons for the substantial quantitative disagreement between theory and experiment observed in the field dependence of the sonic-amplitude oscillation period are discussed. Unannealed samples of the hematite revealed a 60° periodic dependence of the position of the intensity oscillation extrema on magnetic field orientation in the basal plane, which is associated with basal anisotropy of higher than second order. The observation of pronounced (~6×103 Oe) effective magnetic anisotropy fields in the basal plane can be assigned to the existence of large residual strains in such samples. 相似文献
3.
This paper reports the observation of an isostructural electronic phase transition in CeAl2 near 77 Kbar pressure at ambient temperature. The present volume compression data obtained under truly hydrostatic pressure
conditions gives a clear indication of the first order nature of this phase transformation. 相似文献
4.
给出转动相对论系统的Appell方程,讨论相对论力学的四个新型基本动力学函数 在无限小群变换下研究转动相对论系统Appell方程的形式不变性,给出定义和判据 研究形式不变性与Noether对称性与Lie对称性的关系,寻求转动相对论系统的守恒量
关键词:
转动相对论 Appell方程 形式不变性 对称性与守恒量 相似文献
5.
Dispersion properties, birefringence and confinement loss between the circular air-hole photonic crystal fiber (CAHPCF) and
rotational elliptical air-hole photonic crystal fiber (REAHPCF) are investigated numerically by means of a plane-wave expansion
method and a finite element method. Results show that the performances of REAHPCF on flatter dispersion curve, single mode,
high birefringence and low confinement loss is better than that of CAHPCF. 相似文献
6.
《Physics letters. A》1986,113(7):381-383
High pressure electrical resistance experiments performed on a single crystal of CeAl2 allow one to determine a characteristic line in the pressure-temperature plane where a continuous passage from weak to strong Kondo behaviour is observed. This line is not associated with any sizeable volume anomaly as shown by X-ray experiments. 相似文献
7.
We report specific heat measurements on a CeAl2 single crystal between 0.02 and 1 K. Above 0.08 K, we found C0 = γT + βT3 with γ = (130±0.5) mJ/K2mole and β = (142±1) mJ/K4mole in good agreement with previous results above 0.3 K. Below 0.08 K, an excess specific heat CN = αT?2 with α = (6.4±1) mJK/mole was detected and interpreted in terms of hyperfine splitting of the Al27 nuclear states. Our results suggest that in CeAl2 (complex) antiferromagnetism coexists with the Kondo effect at least down to 20 mK. 相似文献
8.
The band structure for the ground state is obtained for CeCu2Si2 and CeAl3 within the local-density approximation (LDA). Subsequently, the quasiparticle band structure is calculated on the basis of the Kondo Lattice Ansatz (KLA) for the Cerium 4f state using the LDA potential parameters for all other electrons. The KLA requires the specification of both the symmetry of the scattering channel, which is taken from the crystal-field (CF) ground state, and the energy dependence of the scattering phase shift, for which a Kondo resonance is assumed. Different results are obtained for two choices of the CF ground-state parameters for CeCu2Si2. Based on our results the low temperature specific heat is discussed. 相似文献
9.
We report on specific heat measurements of (La1–x
Ce
x
)Al2 samples, with 1.5 a/ox100 a/o, performed in magnetic fields of up to 5 T between 0.3 and 10 K. In the Ce rich alloys, and especially in CeAl2, a-type peak of an antiferromagnetic phase transition, and at lower temperatures spin waves and very large electronic contributions are clearly visible. In higher magnetic fields, that is when antiferromagnetic order can be suppressed, the specific heat of the alloys exhibits a broadened Schottky peak. All these phenomena add up tok ln 2, i.e. to the correct entropy change per single Ce3+ ion in its
7 crystal field ground state.We interpret experimental results as an interplay between cooperative magnetism and the single-ion Kondo effect which describes a gradual turning off of one magnetic moment. The broadening of the Schottky peak is directly related to the Kondo temperatureT
K
, which we determine with a simple resonance level model.T
K
increases by an order of magnitude whenx increases from 1.5 a/o to 100 a/o. This is interpreted as caused by a lattice contraction.A quadraticx dependence of the Néel temperature suggests that (forTT
K
) stable Ce moments can only exist through pair interactions. The very large (and almost field independent) specific heat term linear in temperature with a coefficient=135 mJ/K2 mole for CeAl2 is attributed to the Kondo effect—still present in the antiferromagnetically ordered state. Our evaluation of the experimental data is backed by a molecular field theory for a simplified antiferromagnetic structure combined with the simplest possible Kondo theory.Preliminary results have been presented at the Int. Conf. on Magnetic Alloys and Oxides, Haifa 1977 [Bredl, C.D., Steglich, F.: J. Magnetism and Magnetic Materials, in press] 相似文献
10.
The origin of the elastic inconsistency ofdaf, mas andgtf models for non-cubic solids and the failure of their force constants to comply with all the rotational invariance conditions
are analysed by resolving the atomic displacements of face-centred tetragonal indium along three mutually perpendicular directions.
It is shown that a lattice dynamical model suffers from these deficiencies as a consequence of its neglect of three-body interactions
as well as the mixed neighbour interactions associated with the angular forces, while thecgw model which incorporates both these interactions is elastically consistent and its potential energy rotationally invariant.
The degree of equivalence that exists among the force constants ofdaf, mas, gtf andcgw models, the distortions introduced by the elastic inconsistency into the phonon dispersion curves of fct indium as well as
the consequences of imposing the rotational invariance conditions on the force constants of a lattice dynamical model are
discussed. 相似文献
11.
《Physics letters. [Part B]》1986,173(4):413-416
A large class of conformally invariant models in two dimensions is realised by constraining free fermion theories. The Fock spaces of the constrained theories are described, using the representation theory of affine Kac-Moody algebras. The results are extended to superconformally invariant theories. Projections of the models, producing consistent two-dimensional field theories, are discussed. 相似文献
12.
13.
We report the existence of a volume collapsed strongly mixed valent state at pressures above 65 K bars in the prototype “concentrated Kondo” system CeAl2 and discuss the relevant energy scales and general phase diagram of CeAl2. To our knowledge this is the first demonstrated example of what should be a large class of systems exhibiting the full diversity of ground states of an Anderson lattice. 相似文献
14.
N Boccara 《Annals of Physics》1973,76(1):72-79
By group-theoretical arguments we predict all the possible anisotropic liquid phases which can appear as a result of the violation of the rotational invariance of the isotropic liquid. We discuss the mathematical nature of the order parameters which are found to be irreducible tensors, the order of the corresponding phase transitions and the stability of the phases against small spatial fluctuations of the order parameter. 相似文献
15.
When the size of CeAl2 and CePt(2+x) particles is reduced to the nanometer scale, antiferromagnetism is suppressed and Kondo behavior predominates, with the Kondo temperature T(K) either decreasing (CeAl2) or increasing (CePt(2+x)) relative to the bulk. Local structure measurements show that these nanoparticles are significantly distorted. While such distortions should strongly affect magnetic and electronic properties, we find they cannot explain the observed changes in T(K). Other size-induced changes to the electronic structure must, therefore, play a significant role. 相似文献
16.
M. Schlott B. Elschner M. Herrmann W. Assmus 《Zeitschrift für Physik B Condensed Matter》1988,72(3):385-389
The heavy fermion systems CeCu2Si2 and CeAl3 are characterized by a huge quasiparticle density of states responsible for the large electronic specific heat. The observation of a Gd3+ electron spin resonance (ESR) in single crystals CeCu2Si2 and in polycrystalline CeAl3 clearly demonstrates the local character of these quasiparticles. Nevertheless, the Gd-spin relaxation shows remarkable anomalies with respect to the isostructural compounds LaCu2Si2 and LaAl3: Probably via RKKY coupling, Ce 4f-spin fluctuations give rise to an enhanced Gd-spin relaxation resulting in an unusual non-linear thermal broadening around the Kondo temperature. From this we obtain information about the temperature dependence of the Ce 4f-spin correlation time. 相似文献
17.
18.
19.
Thermodynamic calculations, developed here, show that a considerable fraction of the observed low-temperature nuclear spin-lattice
relaxation rate and specific heat of CeAl2-both varying linearly with temperature-may be due to the existence of new low-frequency features in the spin-excitation spectrum
of incommensurate magnetic structures. 相似文献
20.
Deser and Nepomechie established a relationship between masslessness and rigid conformal invariance by coupling to a background metric and demanding local Weyl invariance, a method which applies neither to massive theories nor theories which rely upon gauge invariances for masslessness. We extend this method to describe massive and gauge invariant theories using Weyl invariance. The key idea is to introduce a new scalar field which is constant when evaluated at the scale corresponding to the metric of physical interest. This technique relies on being able to efficiently construct Weyl invariant theories. This is achieved using tractor calculus—a mathematical machinery designed for the study of conformal geometry. From a physics standpoint, this amounts to arranging fields in multiplets with respect to the conformal group but with novel Weyl transformation laws. Our approach gives a mechanism for generating masses from Weyl weights. Breitenlohner–Freedman stability bounds for Anti-de Sitter theories arise naturally as do direct derivations of the novel Weyl invariant theories given by Deser and Nepomechie. In constant curvature spaces, partially massless theories—which rely on the interplay between mass and gauge invariance—are also generated by our method. Another simple consequence is conformal invariance of the maximal depth partially massless theories. Detailed examples for spins s?2 are given including tractor and component actions, on-shell and off-shell approaches and gauge invariances. For all spins s?2 we give tractor equations of motion unifying massive, massless, and partially massless theories. 相似文献