Dynamic compensation temperature in kinetic spin-5/2 Ising model on hexagonal lattice

We present a study of the dynamic behavior of a two-sublattice spin-5/2 Ising model with bilinear and crystal-field interactions in the presence of a time-dependent oscillating external magnetic field on alternate layers of a hexagonal lattice by using the Glauber-type stochastic dynamics. The lattice is formed by alternate layers of spins σ=5/2 and S=5/2. We employ the Glauber transition rates to construct the mean-field dynamic equations. First, we investigate the time variations of the average sublattice magnetizations to find the phases in the system and then the thermal behavior of the dynamic sublattice magnetizations to characterize the nature (first- or second-order) of the phase transitions and to obtain the dynamic phase transition (DPT) points. We also study the thermal behavior of the dynamic total magnetization to find the dynamic compensation temperature and to determine the type of the dynamic compensation behavior. We present the dynamic phase diagrams, including the dynamic compensation temperatures, in nine different planes. The phase diagrams contain seven different fundamental phases, thirteen different mixed phases, in which the binary and ternary combination of fundamental phases and the compensation temperature or the L-type behavior strongly depend on the interaction parameters.     

Phase diagrams in mixed spin-3/2 and spin-2 Ising system with two alternative layers within the effective-field theory

The phase diagrams in the mixed spin-3/2 and spin-2 Ising system with two alternative layers on a honeycomb lattice are investigated and discussed by the use of the effective-field theory with correlations. The interaction of the nearest-neighbour spins of each layer is taken to be positive (ferromagnetic interaction) and the interaction of the adjacent spins of the nearest-neighbour layers is considered to be either positive or negative (ferromagnetic or anti-ferromagnetic interaction). The temperature dependence of the layer magnetizations of the system is examined to characterize the nature (continuous or discontinuous) of the phase transitions and obtain the phase transition temperatures. The system exhibits both second-and first-order phase transitions besides triple point (T P ), critical end point (E), multicritical point (A), isolated critical point (C) and reentrant behaviour depending on the interaction parameters. We have also studied the temperature dependence of the total magnetization to find the compensation points, as well as to determine the type of behaviour, and N-type behaviour in N′eel classification nomenclature existing in the system. The phase diagrams are constructed in eight different planes and it is found that the system also presents the compensation phenomena depending on the sign of the bilinear exchange interactions.     

Multilayer transition in a spin-1 Blume–Capel model with RKKY interaction and quantum transverse anisotropy

Using mean-field theory, we have studied the effect of quantum transverse anisotropies with RKKY interaction on the multi-layer transition and magnetic properties of the spin-1 Blume--Capel model of a system formed by two magnetic multi-layer materials, of different thicknesses, separated by a non-magnetic spacer of thickness M. It is found that the multilayer magnetic order--disorder transition temperature depends strongly on the value of the transverse anisotropy. The multilayer transition temperature decreases when increasing the transverse anisotropy. Furthermore, there exists a critical quantum transverse anisotropy Δ_xL beyond which the separate transitions occur in the two magnetic layers. The critical transverse anisotropy Δ_xL decreases (increases) on increasing the non-magnetic spacer of thickness M (on increasing the crystal field), and Δ_xL undergoes oscillations as a function of the Fermi level.     

On the logical foundations of the Jauch-Piron approach to quantum physics

We make a critical analysis of the basic concepts of the Jauch-Piron (JP) approach to quantum physics. Then, we exhibit a formalized presentation of the mathematical structure of the JP theory by introducing it as a completely formalized syntactic system, i.e., we construct a formalized languageL _e and formally state the logical-deductive structure of the JP theory by means ofL _e . Finally, we show that the JP syntactic system can be endowed with an intended interpretation, which yields a physical model of the system. A mathematical model endowed with a physical interpretation is given which establishes (in the usual sense of the model theory) the coherence of the JP syntactic system.     

Nonmonotonic external field dependence of the magnetization in a finite Ising model: Theory and MC simulation

Using field theory and Monte Carlo (MC) simulation we investigate the finite-size effects of the magnetization M for the three-dimensional Ising model in a finite cubic geometry with periodic boundary conditions. The field theory with infinite cutoff gives a scaling form of the equation of state where is the reduced temperature, h is the external field and L is the size of system. Below and at the theory predicts a nonmonotonic dependence of f(x,y) with respect to at fixed and a crossover from nonmonotonic to monotonic behaviour when y is further increased. These results are confirmed by MC simulation. The scaling function f(x,y) obtained from the field theory is in good quantitative agreement with the finite-size MC data. Good agreement is also found for the bulk value at . Received 20 July 1999 and Received in final form 11 November 1999     

Continuum of compensation points in the mixed spin Ising ferrimagnet with four-spin interaction and next-nearest neighbor coupling

We investigate the magnetic properties of the mixed spin-1/2 and spin-1 Ising ferrimagnetic system with four-spin interaction J₄ and next-nearest neighbor (NNN) coupling J′. We perform exact ground-state calculations and use the finite cluster approximation, based on a single cluster theory, to derive the state equations for the two-dimensional square lattice. The main attention has been paid to the study of the phase diagram for both the transition and compensation temperatures. We find a number of characteristic behaviors. The model with only NNNs induces one compensation point while the four-spin interaction does not. The investigation of the model with both interactions shows a number of characteristic behaviors. In particular, the presence of the four-spin interaction, according to J₄ and J′, may lead to one, two or possibly a continuum of compensation points. This phenomenon may have important applications in technology such as thermomagnetic writing and erasing at the compensation point.     

Electroweak currents as a consequence of the gauge symmetry of lepton flavors and of the seesaw spectrum of neutrino masses

Consequences of the hypothesis that the Sp(pn/2) symplectic group is a broken gauge group of (n) lepton flavors are considered. An invariant Majorana mass is impossible in Sp(pn/2). A dynamical spontaneous breaking of Sp(pn/2) is admissible only if the number of flavors is n = 6and if, simultaneously, parity (R,L symmetry) violation occurs. The action of the seesaw mechanism generates here three light and three heavy Dirac neutrinos. The disregard of heavy particles in an R,L-symmetric system of weak and electromagnetic interactions (R + L vector currents) leads to a theory featuring parity nonconservation and axial anomalies. Only a weak left-handed (L) and a total (R + L) electromagnetic current do not have anomalies and remain independent of high-mass physics. These are precisely Standard Model currents.     

Effect of local variations of the laminar flame speed on the global finger-flame acceleration scenario

Numerous formulations describing the dynamics and morphology of corrugated flames, including the scenarios of flame acceleration, are based on a “geometrical consideration”, where the wrinkled-to-planar flame velocities ratio, S_w /S_L , is evaluated as the scaled flame surface area, while the entire combustion chemistry is immersed into the planar flame speed S_L , which is assumed to be constant. However, S_L may experience noticeable spatial/temporal variations in practice, in particular, due to pressure/temperature variations as well as non-uniform distribution of the equivalence ratio and/or that of combustible or inert dust impurities. The present work initiates the systematic study of the impact of the local S_L -variations on the global flame evolution scenario. The variations are assumed to be imposed externally, in a manner being a free functional of the formulation. Specifically, the linear, parabolic and hyperbolic spatial S_L -distributions are incorporated into the formulations of finger flame acceleration in pipes, and they are compared to the case of constant S_L . Both two-dimensional channels and cylindrical tubes are considered. The conditions promoting or moderating flame acceleration are identified, and the revisited equations for the flame shape, velocity and acceleration rate are obtained for various S_L -distributions. The theoretical findings are validated by the computational simulations of the reacting flow equations, with agreement between the theory and modelling demonstrated.     

Ferrimagnetism in two antiferromagnetic transverse Ising thin films

The phase diagrams and temperature dependences of total magnetization m_T in two antiferromagnetic transverse Ising thin films with same thickness L (L = 4), consisting of two (A and B) layers, are studied by the uses of the effective-field theory with correlations and the mean-field theory. The A and B layers are consisted of spin-1/2 atoms and they have opposite spin directions. Two magnetic structures are discussed and they exhibit rather different and characteristic behaviors for the magnetic properties. Many characteristic behaviors observed in standard ferrimagnetic materials as well as novel phenomena have been obtained for the thermal variations of m_T in the both systems, when the crystallographically equivalent conditions between the A and B layers are broken.     

Irreversible quantum mechanics in the neutralK-system

The neutral kaon system is used to test the quantum theory of resonance scattering and decay phenomena. The two dimensional Lee-Oehme-Yang theory with complex Hamiltonian is obtained by truncating the complex basis vector expansion of the exact theory in rigged Hilbert space. This can be done forK ₁ andK ₂ as well as forK _S andK _L , depending upon whether one chooses the (self-adjoint, semibounded) Hamiltonian as commuting or noncommuting withCP. As an unexpected curiosity, one can show that the exact theory (without truncation) predicts long-time 2π decays of the neutral kaon system even if the Hamiltonian conservesCP.     

Temperature dependence of the exchange interaction constant in iron garnet films

The spin-wave resonance method is used to investigate the temperature dependence of the exchange interaction constant A in iron garnet films. The experimental results are compared with theoretical results based on the theory of second-order phase transitions. It is shown that the temperature dependence A(T) for films of pure yttrium iron garnet is different from A(T) for films exhibiting a point of compensation of the magnetic moment. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 7, 528–532 (10 April 1996)     

Mixed-Spin Ising Model in an Oscillating Magnetic Field and Compensation Temperature

Godoy et al. (Phys. Rev. B 69, 054428, 2004) presented a study of the magnetic properties of a mixed spin (1/2,1), Ising ferrimagnetic model on a hexagonal lattice without an oscillating magnetic field. They employed dynamic mean-field calculations and Monte Carlo simulations to find the compensation point of the model and to present the phase diagrams. It has been found that the N-type compensation temperature appears only when the intrasublattice interaction between spins in the σ sublattice is ferromagnetic. Moreover, the system only undergoes a second-order phase transition. In this work, we extend the study a dynamic compensation temperature of a mixed spin-1/2 and spin-1 Ising ferrimagnetic system on a hexagonal lattice in the presence of oscillating magnetic field within the framework of dynamic mean-field calculations. We find that the system displays the N-type compensation temperature. We also calculate dynamic phase diagrams in which contain the paramagnetic, ferrimagnetic, nonmagnetic fundamental phases and two different mixed phases, depending on the interaction parameters and oscillating magnetic field. The system also exhibits tricritical and reentrant behaviors.     

Ferrimagnetic order in the mixed garnet (Y1− x Gd x )3Fe5O12

Ferrimagnetic order in the mixed rare-earth iron garnet (Y₁?_?? _x Gd _x )₃Fe₅O₁₂ system has been reinvestigated to cover the temperature range 5.0 to 700?K. The magnetization versus temperature exhibits a systematic variation with changing concentration x. The ferric-ion exchange coupling is strong enough to determine the Curie temperature ≈559?K for all the values x. The compensation temperature at which the magnetization crosses zero (shows the minimum) demonstrates the applicability of the three-sublattice model. The magnetic moment at 5.0?K indicates reasonable agreement with the relation n _B?=?|21x???5.0|μ_B for the (Y₁?_?? _x Gd _x )₃Fe₅O₁₂ system. The compensation temperature decreases with decreasing x from 1.0 and reaches zero near x?=?0.24. An enlargement of coercive force in the hysteresis loop for the low-field M-H curve is clearly seen in near the compensation temperature, indicating that a single domain is formed and the rotation of this single domain occurs without building up a multidomain structure.     

Global Hilbert Expansion for the Vlasov-Poisson-Boltzmann System

The dynamics of an electron gas in a constant ion background can be decribed by the Vlasov-Poisson-Boltzmann system at the kinetic level, or by the compressible Euler-Poisson system at the fluid level. We prove that any solution of the Vlasov-Poisson-Boltzmann system near a smooth local Maxwellian with a small irrotational velocity converges global in time to the corresponding solution to the Euler-Poisson system, as the mean free path ε goes to zero. We use a recent L ² − L ^∞ framework in the Boltzmann theory to control the higher order remainder in the Hilbert expansion uniformly in ε and globally in time.     

氧离子轰击引起钽的L壳层X射线发射截面的研究

在北京原子能研究院串联加速器上,利用20—45 MeV的O⁵⁺轰击Ta靶,研究靶的L壳层X射线. 给出了Ta的L壳层各亚壳层Ll,Lα,Lβ和Lγ X射线发射截面的比值,并且与ECPSSR理论计算做了比较. 结果表明,在误差范围内比值σ(Ll)/σ(Lα)、σ(Lβ)/σ(Lα)和σ< 关键词： L壳层X射线')" href="#">L壳层X射线 发射截面 ECPSSR理论     

Dynamic compensation temperature in the mixed spin-1 and spin-2 Ising model in an oscillating field on alternate layers of a hexagonal lattice

The dynamic behavior of a mixed spin-1 and spin-2 Ising system with a crystal-field interaction in the presence of a time-dependent oscillating external magnetic field on a hexagonal lattice is studied by using the Glauber-type stochastic dynamics. The lattice is formed by alternate layers of spins σ=1$\sigma =1$ and S=2. The Hamiltonian model includes intersublattice, intrasublattice and crystal-field interactions. The set of mean-field dynamic equations is obtained by employing the Glauber transition rates. Firstly, we study time variations of the average sublattice magnetizations in order to find the phases in the system, and the thermal behavior of the average sublattice magnetizations in a period or the dynamic sublattice magnetizations to obtain the dynamic phase transition points as well as to characterize the nature (continuous and discontinuous) of transitions. Then, the behavior of the dynamic total magnetization as a function of the temperature is investigated to find the dynamic compensation points as well as determine the type of behavior. We also present the dynamic phase diagrams for both presence and absence of the dynamic compensation temperatures in the nine different planes. According to the values of Hamiltonian parameters, besides the paramagnetic (p), antiferromagnetic (af), ferrimagnetic (i) and non-magnetic (nm) fundamental phases, eight different mixed phases and the compensation temperature or L- and N-types behavior in the Néel classification nomenclature exist in the system.     

Nonlocal electron transport and cross-resistance peak in NSN heterostructures

A microscopic theory describing the peak in the temperature dependence of the nonlocal resistance of three-terminal NSN devices is developed. This peak emerges at sufficiently high temperatures as a result of the competition between quasiparticle/charge imbalance and subgap (Andreev) contributions to the conductance matrix. Both the height and the shape of this peak demonstrate the power law dependence on the superconductor thickness L in contrast to the zero-temperature nonlocal resistance, which decays (roughly) exponentially with an increase in L. A similar behavior was observed in recent experiments. The text was submitted by the authors in English.     

Renormalization group treatment of the scaling properties of finite systems with subleading long-range interaction

The finite size behavior of the susceptibility, Binder cumulant and some even moments of the magnetization of a fully finite O(n) cubic system of size L are analyzed and the corresponding scaling functions are derived within a field-theoretic ɛ-expansion scheme under periodic boundary conditions. We suppose a van der Waals type long-range interaction falling apart with the distance r as r ^{- (d + σ)}, where 2 < σ < 4, which does not change the short-range critical exponents of the system. Despite that the system belongs to the short-range universality class it is shown that above the bulk critical temperature T _c the finite-size corrections decay in a power-in-L, and not in an exponential-in-L law, which is normally believed to be a characteristic feature for such systems. Received 8 August 2001