The Role of Nuclear Nanoprobes in Inducing Magnetic Ordering in Graphite

In this article several aspects concerning the induction of magnetic ordering in graphite via proton bombardment using nuclear nanoprobes are addressed such as proton range and lateral straggling, defect densities, heat load, and simultaneous impurity analysis via particle induced X-ray emission.     

Sobolev gradient approach for the time evolution related to energy minimization of Ginzburg–Landau functionals

The Sobolev gradient technique has been discussed previously in this journal as an efficient method for finding energy minima of certain Ginzburg–Landau type functionals [S. Sial, J. Neuberger, T. Lookman, A. Saxena, Energy minimization using Sobolev gradients: application to phase separation and ordering, J. Comput. Phys. 189 (2003) 88–97]. In this article a Sobolev gradient method for the related time evolution is discussed.     

Thermodynamics of some layered Ising models

Thermodynamic properties of some inhomogeneous Ising models with layered distribution of couplings are studied. In particular, the specific heat is investigated in detail, both analytically and numerically. It is shown that different ordering mechanisms, namely ordering of finite regions and global ordering of infinite range, can occur in different temperature ranges. This results in remarkable structures of the specific heat curves. In addition we investigate the case where the random distribution of couplings extends over an infinite distance in one space direction. The ordinary Ising singularity then changes to one of infinite order provided the transition temperature remains finite.     

Ising model on evolution networks and its application on opinion formation

Many phenomena show that in a favorable circumstance an agent still has an updating possibility, and in an unfavor- able circumstance an agent also has a possibility of holding its own state and reselecting its neighbors. To describe this kind of phenomena an Ising model on evolution networks was presented and used for consensus formation and separation of opinion groups in human population. In this model the state-holding probability p and selection-rewiring probability q were introduced. The influence of this mixed dynamics of spin flips and network rewiring on the ordering behavior of the model was investigated, p hinders ordering of opinion networks and q accelerates the dynamical process of networks. Influence of q on the ordering and separating stems from its effect on average path length of networks.     

Structural changes concurrent with ferromagnetic transition

Ferromagnetic transition has generally been considered to involve only an ordering of magnetic moment with no change in the host crystal structure or symmetry, as evidenced by a wealth of crystal structure data from conventional X-ray diffractometry (XRD). However, the existence of magnetostriction in all known ferromagnetic systems indicates that the magnetic moment is coupled to the crystal lattice; hence there is a possibility that magnetic ordering may cause a change in crystal structure. With the development of high-resolution synchrotron XRD, more and more magnetic transitions have been found to be accompanied by simultaneous structural changes. In this article, we review our recent progress in understand- ing the structural change at a ferromagnetic transition, including synchrotron XRD evidence of structural changes at the ferromagnetic transition, a phenomenological theory of crystal structure changes accompanying ferromagnetic transitions, new insight into magnetic morphotropic phase boundaries (MPB) and so on. Two intriguing implications of non-centric symmetry in the ferromagnetic phase and the first-order nature of ferromagnetic transition are also discussed here. In short, this review is intended to give a self-consistent and logical account of structural change occurring simultaneously with a ferromagnetic transition, which may provide new insight for developing highly magneto-responsive materials.     

Generalized Weyl Ordering and Nonlinear Coherent States

In the context of the nonlinear coherent state(NLCS)theory we introduce the generalized weyl ordering operator formulation.The corresponding generalzied wigner operator turns out to be the Weyl ordered diracδ-operator functions.The completeness relation of NLCS is recast into generalized Weyl ordering form,The relationship between normal ordering,antinormal ordering and the generalized Weyl ordering is established which constitute a self-consistent theory for NLCS.     

Experimental evidence of coupling interaction between charge ordering and spin ordering

In order to experimentally probe into the complicated interaction between charge ordering and spin ordering in manganites,two sets of samples Nd0.5Sr0.5Mn1-xGaxO3(NSMGO) and Nd 0.5Sr0.5Mn1-y CryO3(NSMCO)(0.0 x,y 0.075),have been studied by means of electrical transport,magnetization,electron spin resonance and transmission electron microscopy analysis.By comparing the influence of Cr-doping and Ga-doping in the Nd0.5Sr0.5MnO3(NSMO) system,large difference between the evolution of charge ordering temperature T co in the Cr-doping and the Ga-doping cases is found.In the NSMCO system,the CE-type antiferromagnetic(AFM)/charge ordering(CO) phase disappears with only 2.5 percent Cr doping;but in the NSMGO system,the CE-type AFM/CO phase always exists.This phenomenon indicates that the charge ordering formation is dominated by the spin ordering.As a result,it is experimentally proved that there is strong coupling interaction between charge ordering and spin ordering in NSMO system.     

Thermodynamics of some layered Ising models

Thermodynamic properties of some inhomogeneous Ising models with layered distribution of couplings are studied. In particular, the specific heat is investigated in detail, both analytically and numerically. It is shown that different ordering mechanisms, namely ordering of finite regions and global ordering of infinite range, can occur in different temperature ranges. This results in remarkable structures of the specific heat curves. In addition we investigate the case where the random distribution of couplings extends over an infinite distance in one space direction. The ordinary Ising singularity then changes to one of infinite order provided the transition temperature remains finite.Work performed within the research program of the Sonderforschungsbereich 125 Aachen-Jülich-Köln     

Charge-orbital ordering and Verwey transition in magnetite

Local density approximation + Hubbard U (LDA + U) band structure calculations reveal that magnetite (Fe3O4) forms an insulating charge-orbital-ordered state below the Verwey transition temperature. The calculated charge ordering is in good agreement with that inferred from recent experiments. We found an associated t(2g) orbital ordering on the octahedral Fe2+ sublattice. Such an orbital ordering results primarily from the on-site Coulomb interaction. This finding unravels such fundamental issues about the Verwey transition as the mechanism for the charge ordering and for the formation of the insulating gap, as well as the nonobedience of the Anderson's criterion for the charge ordering.     

Statistical-thermodynamic theory of ordering in a binary film deposited on the surface of a monocrystal

The ordering of a binary monolayer deposited on the surface of a monocrystal is studied. In the case when the structure of the film is equivalent to that of the crystal surface, the ordering in the film is qualitatively similar to that in the bulk of the sample: When the ordering energy is positive there exists an order-disorder phase transition at a certain temperature and for a certain concentration interval. If the structure of the film is different from the structure of the surface, then the film is ordered at all temperatures, independently of the sign of the ordering energy. In this case, in addition to the equilibrium ordered state in the region T < T_* (T_* is a certain temperature which is determined by the composition of the alloy and by the magnitude of the energy shift of the atoms of the film in the field of the substrate), there exists a metastable ordered state in which there is a jump-like change in the ordering at the point T_*, analogous to a first-order phase transition. Possible methods of experimental study of the ordering in films are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 53–57, May, 1987.     

Spontaneous nematic polarisation and deformation in active media

We explore two minimal macroscopic continuous models with feedback interactions inducing spontaneous nematic polarisation and mechanical deformation of the active medium. In the model based on direct feedback between deformation and ordering, linear stability analysis predicts transition to a uniform deformed nematic state but ordering is frustrated in a constrained geometry. In the model mediated by an active or controlling species, transition to either stationary or wave patterns, depending on the sign of interaction coefficients, is predicted by linear analysis and confirmed by numerical simulations.     

Controlling planar and vertical ordering in three-dimensional (In,Ga)As quantum dot lattices by GaAs surface orientation

Anisotropic surface diffusion and strain are used to explain the formation of three-dimensional (In,Ga)As quantum dot lattices. The diffusion characteristics of the surface, coupled with the elastic anisotropy of the matrix, provides an excellent opportunity to influence the dot positions. In particular, quantum dots that are laterally organized into long chains or chessboard two-dimensional arrays vertically organized with strict vertical ordering or vertical ordering that is inclined to the sample surface normal are accurately predicted and observed.     

Generalized Weyl Ordering and Nonlinear Coherent States

In the context of the nonlinear coherent state (NLCS) theory we introduce the generalized Weyl orderingoperator formulation. The corresponding generalized Wigner operator turns out to be the Weyl ordered Dirac δ-operatorfunctions. The completeness relation of NLCS is recast into generalized Weyl ordering form. The relationship betweennormal ordering, antinormal ordering and the generalized Weyl ordering is established which constitute a self-consistenttheory for NLCS.     

Simple Approach to Deriving Some Operator Ordering Formulas in Quantum Optics

In this paper, we provide a simple and neat approach to some operators’ normal ordering and antinormal ordering formulas in quantum optics. Namely, we directly adopt the generating function of Hermite polynomial and the Baker-Hausdorff formula, which differs from the existing ways. As an important byproduct, based on these operator identities, some useful mathematical integral formulas are easily given without really performing these integrations.     

Phase transition in spin systems with various types of fluctuations

Various types ordering processes in systems with large fluctuation are overviewed. Generally, the so-called order–disorder phase transition takes place in competition between the interaction causing the system be ordered and the entropy causing a random disturbance. Nature of the phase transition strongly depends on the type of fluctuation which is determined by the structure of the order parameter of the system. As to the critical property of phase transitions, the concept “universality of the critical phenomena” is well established. However, we still find variety of features of ordering processes. In this article, we study effects of various mechanisms which bring large fluctuation in the system, e.g., continuous symmetry of the spin in low dimensions, contradictions among interactions (frustration), randomness of the lattice, quantum fluctuations, and a long range interaction in off-lattice systems.     

Importance of depletion interactions for structure and dynamics of ferrofluids

The influence of attractive depletion forces on the structure and dynamics of ferrofluids is studied by computer simulations. In the presence of a magnetic field, we find that sufficiently strong depletion forces lead to an assembly of particle chains into columnar structures with hexagonal ordering inside the columns. In a planar shear flow, this ordering is destroyed, leading to strong shear thinning behavior. A pronounced anisotropy of the shear viscosity is observed. The viscosity is found to be largest when the magnetic field is oriented in the gradient direction of the flow.     

Normal ordering and antinormal ordering of the operator （fQ＋gP）n and some of their applications

In this paper by virtue of the technique of integration within an ordered product (IWOP) of operators and the intermediate coordinate-momentum representation in quantum optics, we derive the normal ordering and antinormal ordering products of the operator (f Q + gP )n when n is an arbitrary integer. These products are very useful in calculating their matrix elements and expectation values and obtaining some useful mathematical formulae. Finally, the applications of some new identities are given.     

On the role of mechanical stress in the chemical ordering of nanoalloys

Metallic alloy clusters at equilibrium display an inhomogeneous stress field which may contribute to the chemical ordering and segregation properties. We use the example of cuboctahedral and icosahedral Au-Pd clusters with the same size to compare these properties in systems displaying moderately and highly inhomogeneous stress fields. Metropolis Monte Carlo simulations in the semi-grand canonical ensemble are used with an empirical potential to predict equilibrium configurations. Pressure maps are used to estimate stress on each atom. It is found that when the stress field is moderately inhomogeneous, ordering is dominantly driven by thermodynamic forces. In icosahedral clusters, ordering is found to be the consequence of a balance where thermodynamic forces and mechanical stress may conflict or reinforce each other. Order-disorder transitions are smoother in the systems with higher stress inhomogeneity and it is conjectured that, in icosahedral clusters, disorder may nucleate in the central core.     

受限导致硬椭球液体的取向有序

Monte Carlo模拟研究了两平行硬墙受限下各向异相的硬椭球液体形成的有序结构. 墙壁对椭球粒子的过量吸附和椭球的长短径之比有关;对于高密度的椭球液体,它在一个临界的长短径之比 a/b=2.9处达到最大值,表明在墙表面附近发生了取向有序. 墙表面附近的密度分布和取向序参量进一步证实这结论. 相同密度条件下体相中的取向序参量计算表明体相结构均为各向同性,这是由于体系的密度依然低于各向同性相向相列向转变的临界密度. 该受限椭球液体中墙表面的取向有序是由墙面的几何受限所导致的.