Domain walls and gravitational waves after thermal inflation

Thermal inflation is an attractive solution to the cosmological moduli problem. However, domain walls may be formed after thermal inflation and some mechanisms are needed to eliminate the domain wall before it dominates the Universe. We point out that gravitational waves produced by the dynamics of domain walls may be observed by the pulsar timing experiments and future space-borne gravitational wave detectors, which provides a probe into the period of thermal inflation. We also show that the QCD instanton effect can effectively eliminate the domain walls with producing observable amount of gravitational waves.     

Dynamics of helimagnets with spin polarised currents

We study analytically, spin polarised current induced dynamics of Dzyaloshinskii-Moriya helimagnets within the phenomenological Landau-Lifshitz framework. Similarities and differences between two popular models of dissipative structures (Gilbert and Landau-Lifshitz dissipation) are explored. Analytical results are obtained and discussed for the magnetisation, the wave number and the velocity of the helical magnetisation structures which are analogous to the behaviour of domain walls under spin polarised current in ferromagnets.     

Domain dynamics and magneto-electronics in magnetic thin films and nanowires

Recent theoretical results are highlighted that illustrate some of the interesting phenomena associated with magnetic domain boundary walls. Two problems will be discussed: dynamics associated with domain wall propagation, and effects related to spin transport through domain walls. For the first problem, an example of wall interaction and motion through a random potential will be discussed with reference to the general problem of roughening transitions. Images of domain dynamics in thin films of ion irradiated Co reveal a de-roughening transition associated with long range magnetostatic interactions between pairs of domain walls. A scaling theory of this transition is described in which a curious type of dynamic hysteresis can occur. For the second problem, results from calculations of ballistic charge and spin transport through domain boundary walls are discussed in terms of an effective circuit model.     

Dynamics of <Emphasis Type="Italic">ab</Emphasis>-type domain walls in magnets with quadratic magnetoelectric interaction

The dynamics of the ab-type 180-degree domain walls was studied in weak ferromagnets with quadratic magnetoelectric interaction in alternating magnetic and electric fields. The features of the oscillatory and drift motion of the domain walls are discussed. The drift velocity of the ab-type domain walls as a function of the frequency and phase shift of the external fields is obtained. The possibility of the drift of the domain walls in a purely electric field is established.     

Interaction of a moving domain wall with surface magnetoelastic waves in yttrium orthoferrite

The amplitude-frequency characteristics of magnetoelastic surface waves excited by moving domain walls in a lamellar yttrium orthoferrite samples are discovered and measured. The results of analysis of the effect of magnetoelastic surface waves on the dynamics of domain walls in this orthoferrite are considered. The nonlinear interaction between magnetoelastic surface waves accompanying a moving domain wall is analyzed.     

Domain wall solitons in binary mixtures of Bose-Einstein condensates

The structure and dynamics of the domain walls separating segregated condensates in trapped mixtures of repulsive Bose-Einstein condensates are studied. Our work reveals that, under fairly general conditions, these domain walls behave as independent dynamical entities, which allows us to identify them as constituting a novel class of multicomponent solitons in Bose-Einstein condensates.     

Cross-modulation instability in inhomogeneous normal-dispersion fiber amplifiers

The conditions of the onset of a modulation instability of the signal wave in a doped fiber due to nonlinear cross-modulation interaction with the pump wave are investigated. The analysis takes into consideration the pump depletion and the group-velocity mismatch of the interacting waves. A dispersion relation coupling perturbation parameters with those of pump, analytic expressions governing the integral growth rate of a harmonic perturbation, and other important characteristics determining the dynamics of the signal-wave cross-modulation instability are obtained. Based on computer simulation, the behavior of the above characteristics as a function of the initial signal-wave power, fiber length, and group-velocity mismatch of the pump and signal waves is investigated.     

Dynamics of antiferromagnetic vortices in yttrium orthoferrite domain walls

The total velocity of solitary flexural waves nonlinearly increases with an increase in the velocity of domain walls and becomes saturated at a level of 20 km s^?1; the smaller the wave amplitude, the more rapidly saturation occurs. Counter collisions of solitary flexural waves lead to the formation of a single wave with a difference amplitude moving in the same direction as the wave with a larger amplitude. The experimental results confirm that solitary flexural waves accompany antiferromagnetic vortices at domain walls in yttrium orthoferrite.     

Sense anisotropy of the kink dynamics in an evolutionary equation with broken space symmetry

A nonlinear diffusion-type evolutionary equation that describes the effect of sense anisotropy of velocity when the front of a solitary wave (kink) moves with unequal velocities in the forward and (when an external field reverses sign) backward directions is suggested. A prerequisite for such behavior is space symmetry breaking in the system. The equation is applied to describing the dynamics of 180° domain walls in ferromagnets with negative cubic crystalline anisotropy. The amount of the sense anisotropy effect in YIG may reach 20%.     

Electroacoustic waves confined by a moving domain wall superlattice of a ferroelectric crystal

The dispersion properties of electroacoustic wave modes confined by a superlattice of uniformly moving 180° domain walls in a tetragonal ferroelectric crystal are considered. It is shown that the manifold of partial electroacoustic interfacial waves in the lattice is restricted to the first allowed band, the configuration of which in the plane of spectral variables can significantly vary under the action of the moving domain walls.     

Excitation spectrum and thermodynamics of domain walls in the biaxial ferromagnet

The problem on spectrum of linear excitations in the presence of a moving domain wall in 1D Heisenberg ferromagnet with orthorhombic anisotropy is exactly solved. The explicit expressions for spin waves scattering on the domain wall are obtained. The phase shift of a spin wave, as the result of collision of spin wave with a moving wall, is exactly determined. The change in magnon density of states is calculated from this scattering data, and the contribution of domain walls to the classical low-temperature thermodynamics is found.     

Lattice-scale domain wall dynamics in ferroelectrics

Ferroelectric domain walls are atomically thin, and consequently their dynamics are sensitive to the periodic potential of the underlying lattice. Despite their central role in domain dynamics, lattice-scale effects have never been directly observed. We investigate local domain dynamics in thin film ferroelectrics using atomic-force microscopy. Upon combined dc and ac electric driving, fluctuations in the local piezoresponse are observed. Fourier analysis of the fluctuations reveals the presence of narrow band and broad band noise, and Barkhausen jumps. The narrow band noise is attributed to dynamics associated with lattice-scale pinning and is reproduced by a simple physical model.     

Stabilization of domain walls between traveling waves by nonlinear mode coupling in Taylor-Couette flow

We present a new mechanism that allows the stable existence of domain walls between oppositely traveling waves in pattern-forming systems far from onset. It involves a nonlinear mode coupling that results directly from the nonlinearities in the underlying momentum balance. Our work provides the first observation and explanation of such strongly nonlinearly driven domain walls that separate structured states by a phase generating or annihilating defect. Furthermore, the influence of a symmetry breaking externally imposed flow on the wave domains and the domain walls is studied. The results are obtained for vortex waves in the Taylor-Couette system by combining numerical simulations of the full Navier-Stokes equations and experimental measurements.     

High-temperature memory in multiferroic cobalt–bromine boracite

The observation of the domain dynamics of the ferroelectric–ferroelastic domains near the paraelectric–ferroelectric phase transition is reported. The study was performed by means of high-temperature polarized light microscopy. Close to the phase transition an increase in the number of domain walls was observed. After several heating–cooling cycles around the transition temperature, a memory domain microstructure at high temperature was observed. The possible physical mechanisms responsible for the high-temperature domain dynamics are discussed. Using a complex systems approach the complexity of the domain behavior is characterized.     

Dynamics of domain walls in weak ferromagnets with quadratic magnetoelectric interaction

The dynamics of domain walls of the ab type in weak ferromagnets with a quadratic magnetoelectric interaction has been studied in ac magnetic and electric fields. The specific features of the vibrational and drift motions of the domain walls as functions of parameters of the external fields and characteristics of the material have been discussed. The possibility of drift occuring the domain walls in a purely electric field has been predicted.     

Influence of the reversible adsorption of methyl alcohol on magnetization reversal in ferromagnets

A change in the dynamics of 180° domain walls on the surface of a soft amorphous ferromagnet in methyl alcohol atmosphere is established by means of a magnetooptic method. A reversible decrease in the relaxation frequency of the domain walls near the surface in the presence of methyl alcohol admolecules is observed. This effect is related to the magnetic defects resulting from methyl alcohol adsorption on the ferromagnet surface, which proceeds through hydrogen bonding. Based on earlier data for the influence of the reversible adsorption of water molecules on the domain wall dynamics in ferromagnets, it is concluded that reversible adsorption through the mechanism of hydrogen bond formation considerably affects the domain wall dynamics in soft ferromagnets.     

Domain-Wall Dynamics After Photoexcitations Near neutral-Ionic Phase Transitions

Real-time dynamics of domain walls between the neutral and ionic phases just after photoexcitations is studied by fully solving the time-dependent Schrödinger equation for a one-dimensional extended Peierls-Hubbard (PH) model, not by relying on the adiabatic approximation. The unrestricted Hartree-Fock (HF) approximation is used for electrons, and the lattice displacements are treated classically. Three characteristic time scales are observed: rapid oscillation of ionicity owing to the local charge transfer; slow oscillation of lattice displacements; and even slower and collective motion of domain walls. Steady growth of a metastable domain is achieved after complicated competition of micro domains. The relevance to recently measured, time-resolved photoreflectance spectra in TTF-CA is discussed.     

Dynamics of vortexlike domain walls in triaxial magnetic films with the Goss orientation of the surface

The stationary dynamics of vortexlike domain walls in films with three magnetic axes and Goss orientation of the surface is studied for the first time with a micromagnetic method that exactly takes into account all basic types of interaction (including dipole-dipole interaction). Consideration is carried out using a 2D model of magnetization distribution by numerically solving Landau and Lifshitz’s nonlinear equations with attenuation in the Gilbert form. Dynamic configurations of domain walls are established, and the dependences of the domain wall velocity on an applied magnetic field, damping parameter, and magnetic film thickness are found.     

行波电光相位调制器输出响应的定量分析

从标量波动方程出发,采用傅里叶变换的方法,导出了行波电光相位调制器的时间域输出响应的计算公式。以高斯脉冲调制信号为例,定量计算并讨论了速度不匹配和微波衰减对输出相位调制信号的脉冲形状,峰值,半值宽的影响,所得到的结果,对行波电光调制器的实验研究有很好的参考价值,所给出的公式和方法适用于行波电光调制器的时间域定量分析。