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1.
The Co-sublattice anisotropy in Lu2Co17 consists of four competitive contributions from Co atoms at crystallographically different sites in the Th2Ni17-type of crystal structure, which result in the appearance of a spontaneous spin-reorientation transition (SRT) from the easy plane to the easy axis at elevated temperatures. In order to investigate this SRT in detail and to study the influence of Si substitution for Co on the magnetic anisotropy, magnetization measurements were performed on single crystals of Lu2Co17−xSix (x=0−3.4) grown by the Czochralski method. The SRT in Lu2Co17 was found to consist of two second-order spin reorientations, “easy-plane”–“easy-cone” at TSR1≈680 K and “easy-cone”–“easy-axis” at TSR2≈730 K. Upon Si substitution for Co, both SRTs shift toward the lower temperatures in Lu2Co16Si (TSR1≈75 K and TSR2≈130 K) with the further onset of the uniaxial type of magnetic anisotropy in the whole range of magnetic ordering for Lu2Co17−xSix compounds with x>1 due to a weakening of the easy-plane contribution from the Co atoms at the 6g and 12k sites to the total anisotropy.  相似文献   

2.
On the basis of propositions of the common fluctuation theory, peculiarities of small fluctuations in real physical systems with limited sizes are analyzed. It is established that small fluctuations should necessarily be divided into two types of fluctuations: “small” and “very small”. It is shown that the damping process of “small” fluctuations has relaxation character, while the damping process of “very small” fluctuations is of random character, i.e., it represents a random rectangular signal. The probability density of “very small” fluctuations is shown to be Gaussian. The agreement of the obtained results with experimental data acquired from semiconductor-based devices is analyzed. A relation between the generation–recombination noise and phonon number fluctuations in semiconductors is studied. On the basis of this consideration it is shown that the Schönfeld pulse spectrum preserves its well-known 1/f form only in the range of intermediate frequencies; at lower frequencies the spectrum gets saturated. An expression for the low-frequency limit of Schönfeld pulse 1/f law is obtained.  相似文献   

3.
Anomalies are found in the near-band-edge luminescence properties of Δ2-light-hole indirect excitons in Si1−yCy-based tensilely strained quantum wells (QWs). The experimental spectra exhibit a clear signature of phonon-assisted transitions on the lower energy side of the “no-phonon” transition, which indicates the relevance of “virtual” indirect valleys and in-plane k-dispersion, as opposed to the theoretical prediction that the zone-centered Δ2 valleys take over the conduction band edge. Intervalley scattering between [0 0 1]-Δ2 valleys and in-plane Δ4 valleys is suggested as the underlying mechanism. On the other hand, the experimental evidence was found for “apparently enhanced” quantum-confined Stark red shifts for Si1−yCy-based QWs. However, quantitative estimates are in conflict with the experimental results and predict a blue shift due to exciton weakening which masks the Stark effect as in the case of Δ4-heavy hole excitons in Si1−xGex-based QWs.  相似文献   

4.
Magnetization measurements in fields up to 38 T performed at low temperature on single crystals of the hexagonal Pr(Ni1-xCox)5 compounds for x = 0, 0.05, 0.10 and 0.20 are presented. In PrNi5 we observe highly original behaviour predicted by the knowledge of the Crystalline Electric Field parameters and arising from the existence of a non-magnetic singlet ground state; namely transitions associated with the field induced “anticrossing” and “crossing” of the two lowest states along the [100] and [120] directions, respectively. The measurements performed on the other compounds have allowed us to study the dependence of this behaviour on Co substitutions.  相似文献   

5.
The growth and morphological evolution of molybdenum-oxide microstructures formed in the high temperature environment of a counter-flow oxy-fuel flame using molybdenum probes is studied. Experiments conducted using various probe retention times show the sequence of the morphological changes. The morphological row begins with micron size objects exhibiting polygonal cubic shape, develops into elongated channels, changes to large structures with leaf-like shape, and ends in dendritic structures. Time of probe–flame interaction is found to be a governing parameter controlling the wide variety of morphological patterns; a molecular level growth mechanism is attributed to their development. This study reveals that the structures are grown in several consecutive stages: material “evaporation and transportation”, “transformation”, “nucleation”, “initial growth”, “intermediate growth”, and “final growth”. XRD analysis shows that the chemical compositions of all structures correspond to MoO2.  相似文献   

6.
The mechanism of baryon-anti-baryon pair production in e+e annihilation into hadrons has been studied using the TOPAZ detector at the TRISTAN e+e collider at an average center-of-mass energy of 58 GeV. The distributions of various correlations were compared with two prominent models: the cluster-fragmentation model and the string-fragmentation model. We rejected the cluster-fragmentation model at the 90% C.L. Furthermore, in the context of the string-fragmentation model, we favor the “popcorn” model, rejecting the “diquark” model, where a diquark is considered to be a fundamental entity, at the 95% C.L.  相似文献   

7.
8.
The phonetogram has been recommended as an international tool for voice analysis. However, the capability of this technique to distinguish between different vocal groups has not been clearly established. The purpose of this study was to examine untrained versus trained vocalists using the phonetogram and the fundamental frequency by intensity (F0/SPL) information derived through that method. In this study, “musical” or “controlled” ranges of phonation were stressed rather than “physiological” ranges. Results indicated that (a) characteristic phonetographic profiles may be established for untrained versus trained vocalists, and (b) trained vocalists show significantly increased capability in terms of F0 range and maximum, minimum, and comfortable SPL production. Elicitation of “controlled” phonations may be the key to revealing the underlying vocal capabilities of seemingly different vocal groups.  相似文献   

9.
10.
Topical phenomena in high-energy physics related to collision experiments of heavy nuclei (“Little Bang”) and early universe cosmology (“Big Bang”) involve far-from-equilibrium dynamics described by quantum field theory. One example concerns the role of plasma instabilities for the process of thermalization in heavy-ion collisions. The reheating of the early universe after inflation may exhibit rather similar phenomena following a tachyonic or parametric resonance instability. Certain universal aspects associated to nonthermal fixed points even quantitatively agree, and considering these phenomena from a common perspective can be fruitful.  相似文献   

11.
The high resolution laser Stark spectra of methanol and13C-substituted methanol have been studied up to Stark fields of about 60 000V/cm with the HCN and DCN lasers. Numerous families of absorption lines have been observed in both parallel and perpendicular polarizations. For methanol, the transitions J k =75 64 A, t=0; J k =114 103 E l , t=0; and J k =173 162 E2, t=0 have been identified while the assignments for13C-substituted methanol are J k =148 157 A, t=0; J k =153 142 A+, t=0; J k =107 96 A, t=0; and J k =279 278 E1, t=0. Zero-field frequencies for the assigned transitions are given with improved accuracy over those calculated from available molecular constants, especially for13CH3OH.  相似文献   

12.
A suggestion on how black holes may appear in Das-Jevicki collective field theory is given. We study the behaviour of a “test” particle when energy is sent into the system. A perturbation moving near the potential barrier can create a large-distance black hole geometry where the seeming curvature singularity is at the position of the barrier. In the simplest “static” case the exact D=2 black hole metric emerges.  相似文献   

13.
Gluon bremsstrahlung in scattering events with high transverse momentum jets is expected to increase markedly with the hardness (∑ET) of the primary event. Within perturbative QCD we estimate a probability of order unity to see additional minijets with ET 15 GeV in “dijet” events with ∑ET > 400 GeV. The veto of such minijets is a promising background rejection tool for the Higgs search at the LHC.  相似文献   

14.
We describe the fabrication and optical properties of a 3λ/2 InGaN/GaN-based microcavity using “upper” and “lower” silica/zirconia mirrors. The fabrication of this structure involved selective removal of an AlInN layer following multistep thinning of a free-standing GaN substrate. Photoluminescence spectra show a narrowing of the excitonic emission from InGaN/GaN quantum wells in the microcavity, giving a cavity quality factor Q exceeding 400.  相似文献   

15.
The resistivity , the magnetoresistance Δ and the Hall resistivity H of alloys up to 30% Mn have been measured using amorphous ribbons of these materials. The temperature and field dependences of and H suggest a variety of structural and spin scattering centers; in particular, (T) appears to be governed by structural (isotropic) scattering centers while H(T) is dominated by topological (anisotropic) spin scattering centers, one of which probably is a “spin-hole”.  相似文献   

16.
Yb(Ba1−xSrx)2Cu4O8 (0.1x0.3) superconductors of the YBa2Cu4O8(“124”) structure were successfully synthesized using an O2-hot-isostaticc-pressing (HIP) technique. The samples were characterized with respect to the crystal structure and superconducting properties. The lattice parameters of the samples decreased as the substitution of Sr for Ba proceeded. The superconducting transition temperatures of all the Yb-“124” samples were more or less the same, being around 80 K.  相似文献   

17.
The structural and magnetic behavior of the perovskite insulator La0.9Ca0.1MnO3 were studied as a function of temperature from 15 to 300 K by neutron powder diffraction. Although this compound shows an anomalous response of the lattice parameters around Tc (150 K), the behavior of the oxygen/manganese Debye-Waller factors is in clear contrast to its “colossal magnetoresistance” (CMR) counterpart La0.65Ca0.35MnO3. We speculate that the difference is intimately associated with the metal-insulator transition in the latter compound.  相似文献   

18.
2D spectra, particularly for homonuclear correlation, can show a variety of artifactual signals in the F1 domain. Common sources include carry-over of signal modulation from one transient to the next (“rapid pulsing artifacts”) and systematic variations in room temperature (“parallel diagonals”). In both cases there is one very simple expedient which can greatly reduce the impact of these sources of error. Multidimensional data sets are almost invariably recorded by simply incrementing or decrementing evolution periods, largely for reasons of convenience and historical precedent. If instead the sampling of the evolution periods is carried out in random order, the perturbations responsible for the sharp F1 signals in the conventional experiment manifest themselves as t1 noise. Since the randomized acquisition redistributes coherent artifactual signals randomly in F1, the maximum artifactual signal is substantially reduced in the randomized experiment and no longer appears in the form of misleading distinct peaks.  相似文献   

19.
We report on magnetooptical studies of II–VI semiconductor quantum wells with a parabolic shape of the potential grown on the basis of Cd1−xMnxTe. Photoluminescence excitation measurements revealed a series of peaks equidistant in energy associated with interband optical transitions between “harmonic oscillator states”. We observed the Zeeman splitting for heavy-hole excitons up to the subband index n=5. From the comparison of the experimental data with numerical calculations for the Zeeman splitting it was possible to determine the correct shape of the potential.  相似文献   

20.
We present a coherent scenario for the physics of cuprate superconductors, which is based on a charge-driven inhomogeneity, i.e. the “stripe phase”. We show that spin and charge critical fluctuations near the stripe instability of strongly correlated electron systems provide an effective interaction between the quasiparticles, which is strongly momentum, frequency, temperature and doping dependent. This accounts for the various phenomena occurring in the overdoped, optimally and underdoped regimes both for the normal and the superconducting phase.  相似文献   

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