Local orientational order in the stockmayer model

A new method based on the local analysis of the orientational order has been presented for analysis of the phase behavior of the Stockmayer fluid. A quantity has been introduced to quantitatively describe the ordering degree of particles at small distances. It has been used to analyze the phase diagram of the model under consideration.     

Local structural order in nanostructured hematite

Nanostructured α-Fe₂O₃ powders were prepared by high-energy ball milling. The milling process spans grinding times from 30 min to 24 h. The as-milled samples were characterized by means of ⁵⁷Fe Mössbauer spectrometry, Rietveld analysis of X-ray diffraction data and particle size analysis. The obtained results evidence the presence of disordered hematite characterized by a hyperfine field distribution with a well-behaved dependence on the mean crystallite size for which the mean hyperfine field decreases asymptotically as the grain size decreases. A new relationship is proposed in order to describe such behavior. Finally the presence of superparamagnetic grains, the occurrence of a partial topotactic phase transformation into a spinel phase and tool induced contamination are also presented and discussed.     

Short-range order in the Fe-B-Sn amorphous system

Melt quenched FeBSn samples of different compositions were prepared with three different quenching rates and analyzed by Mössbauer spectroscopy and X-ray diffraction. In a previous work, the glass-forming tendency in this system was analyzed, In the present work, the short-range order is studied and an improvement in the determination of the glass-forming composition range is achieved. Mössbauer spectra were fit using hyperfine field distributions.     

Local order in the bulk and surface of liquid K-Pb alloy

Ordering in the bulk and surface of liquid K-Pb alloy has been studied throughout the bulk concentration range. At low K concentrations, the liquid alloy is strongly ordered both in the bulk and on the surface. The existence of the zintl structure in the liquid alloy is predicted to be predominant below 0.6 atomic fraction of K. While above this concentration a complex of the form K₃Pb₂ is suggested to be present. PACS  28.52.Fa; 65.70.+y; 61.20.-p; 61.82.Bg     

Local magnetic order in silicon implanted with high-energy ions

A room-temperature local magnetic order has been detected in silicon implanted with high-energy Kr⁺ and Xe⁺ ions. The evidence of the presence of the local magnetic order are the electron magnetic resonance lines with g-factor values of about 2.2 and 3.4, the hysteresis of the resonance magnetic field values of these lines, the anisotropy characteristic of ferromagnets, and the broadening. The ordering effect is retained after the annealing of samples at temperatures of no higher than 1270 K.     

Local magnetic order vs superconductivity in a layered cuprate

We report on the phase diagram for charge-stripe order in La1.6-xNd0. 4SrxCuO4, determined by neutron and x-ray scattering studies and resistivity measurements. From an analysis of the in-plane resistivity motivated by recent nuclear-quadrupole-resonance studies, we conclude that the transition temperature for local charge ordering decreases monotonically with x, and hence that local antiferromagnetic order is uniquely correlated with the anomalous depression of superconductivity at x approximately 1 / 8. This result is consistent with theories in which superconductivity depends on the existence of charge-stripe correlations.     

Local structural order and single-particle dynamics in metallic glass

The atomic dynamics of the amorphous metallic alloy Al₅₀Cu₅₀ is investigated in this work. The critical glass-forming temperature is defined from the behavior change of the Wendt—Abraham parameter and the pair-correlation entropy, and is T _c ≈ 500 K. It is shown that the power-fractional memory function allows us to describe in the framework of the mode-coupling theory the time dependences of the incoherent scattering functions obtained from the atomic dynamic simulations for the wide region of temperatures (T = 100–2000 K).     

Local crystalline order in a 2D colloidal glass former

A mixture of two types of super-paramagnetic colloidal particles with long-range dipolar interaction is confined by gravity to a flat interface of a hanging water droplet. The particles are observed by video microscopy and the dipolar interaction strength is controlled by an external magnetic field. The local structure as obtained by pair correlation functions and bond order statistics is investigated as a function of system temperature and relative concentration. Although the system has no long-range order and exhibits glassy dynamics, different types of stable crystallites coexist. The local order of the globally disordered structure is explained by a small set of specific crystal structures. The statistics of crystal unit cells show a continuous increase of local order with decreasing system temperature as well as a dependence on sample history and local composition.     

Magnetic order and transport in the heavy-fermion system CeCuAu

We report on extensive elastic neutron scattering to determine the wave vector of the magnetic order in CeCu_6-xAu_x single crystals for x > 0.1. For all values of x investigated (0.2, 0.3, 0.5, 1.0) we find long-range incommensurate antiferromagnetic order with an ordering vector (0.625 0.275) for x =0.2, nearly unchanged for x =0.3, and (0.59) for x =0.5, staying roughly the same for x =1.0. In addition, short-range correlations are observed for x =0.2, reminiscent of those found previously for x =0.1. The ordered magnetic moment is found to increase rapidly for small x, and more slowly for the larger x values. The increase of the specific-heat anomaly at the ordering temperature with x is in qualitative accord with this behavior. Finally, data of the electrical resistivity for current flow along the three crystallographic directions are presented, showing a clear signature of the magnetic order. A theoretical interpretation of the interplay of magnetic order and transport in terms of (i) the partial suppression of the Kondo effect by the staggered magnetization and (ii) the anisotropic band structure induced by the staggered field is shown to account well for the data, provided the ordering vector is close to 2 k F, where k F is a typical Fermi momentum. Received: 20 February 1998 / Accepted: 17 April 1998     

Nonchaotic random behaviour in the second order autonomous system

Evidence is presented for the nonchaotic random behaviour in a second-order autonomous deterministic system. This behaviour is different from chaos and strange nonchaotic attractor. The nonchaotic random behaviour is very sensitive to the initial conditions. Slight difference of the initial conditions will generate wholly different phase trajectories. This random behaviour has a transient random nature and is very similar to the coin-throwing case in the classical theory of probability. The existence of the nonchaotic random behaviour not only can be derived from the theoretical analysis, but also is proved by the results of the simulated experiments in this paper.     

Local atomic order and optical properties in amorphous and laser-crystallized GeTe

In this work we study the role of short-range order changes upon amorphization on the optical properties of GeTe – a prototype phase change material employed for optical data storage. It is found that the profound change in the absorption is due to changes in the matrix elements of the optical transitions. The importance of the local distortions in the crystalline phase for the optical absorption are revealed as well. Modifying the degree of the distortions has a significant impact on the optical properties of the crystalline state and should therefore become a promising instrument to improve material properties for storage applications.Furthermore we study the effect of electron–electron and electron–hole interactions on the optical properties. This is achieved by evaluating many-body effects in the crystalline phase through a GW correction of eigenvalues and the solution of the Bethe–Salpeter equation. To cite this article: W. Wełnic et al., C. R. Physique 10 (2009).     

Local icosahedral order and thermodynamics of simulated amorphous Fe

Local icosahedral order and thermodynamics of amorphous Fe have been analyzed in detail for models containing 3000 atoms, which were obtained by the molecular dynamics (MD) method. Models were obtained by cooling from the melt. Local order in models has been analyzed by using the technique proposed by Honeycutt and Andersen; we found an existence of icosahedral order in the system. Moreover, structural properties of models were also studied via radial distribution function (RDF), static structure factor, mean atomic distances, coordination number and bond-angle distributions. Glass transition temperature, heat capacity and potential energy of the system were found in addition to the evolution of structure and mean-squared displacement (MSD) of atoms upon cooling from the melt toward the glassy state. We found the glass transition temperature of simulated liquid Fe via temperature dependence of potential energy and it is close to that observed previously in the literature, i.e. T_g≈1070 K. Calculations showed that structural properties of amorphous Fe models with the Pak-Doyama interatomic potential agreed well with the experimental data.     

Local order parameter near the critical point: A Monte Carlo study

The probability distribution of the local magnetization in a Heisenberg ferromagnet has been investigated near the critical temperature. The distribution function depends strongly upon the number of atoms generating the local field. A cusp-like critical broadening is observed with different behavior above and below the critical temperature.     

分数阶Newton-Leipnik系统的动力学分析

依据分数阶线性系统的稳定性理论,研究了具有双重混沌吸引子的Newton-Leipnik系统取不同分数阶时的动力学行为.研究表明该系统具有逆向Hopf分岔过程,即随着阶数的下降,分数阶Newton-Leipnik系统由双重混沌吸引子突变为单吸引子,其动力学行为将由混沌态历经短暂的周期态后收敛于稳定的平衡点.     

分数阶统一混沌系统的投影同步

改变系统参数计算了分数阶统一系统的最大Lyapunov指数和关联维数,研究了分数阶统一系统的动力学行为.基于线性系统的稳定判定准则,设计了一种同步方案,实现了分数阶统一混沌系统的投影同步.通过对分数阶Chen系统、分数阶Lü系统和分数阶类Lorenz系统投影同步的数值模拟,进一步验证了所提出方案的有效性.     

Local order in light emitting porous silicon studied by XEOL and TEY

The local structure of porous silicon has been studied exciting its optical luminescence by X-rays (XEOL). The photoluminescence yield and the total electron yield (TEY), recorded simultaneously as a function of the X-ray energy at the Si K edge, give rise to the extended X-ray absorption fine structures (EXAFS). Analysis of EXAFS data confirms that the optical luminescence of porous Si originates from the nanocrystalline cores and shows that XEOL–EXAFS and TEY–EXAFS are sensitive to different Si local environment. It can be assumed that XEOL–EXAFS is related only to the light emitting sites while TEY–EXAFS is sampling both luminescent and non-luminescent Si sites.