Motion Of Domain Boundaries Research Articles

A high-order finite difference method for moving immersed domain boundaries and material interfaces

We present a high-order sharp treatment of immersed moving domain boundaries and material interfaces, and apply it to the advection-diffusion equation in two and three dimensions. The spatial discretization combines dimension-split finite difference schemes with an immersed boundary treatment based on a weighted least-squares reconstruction of the solution, providing stable discretizations with up to sixth order accuracy for diffusion terms and third order accuracy for advection terms. The temporal discretization relies on a novel strategy for maintaining high-order temporal accuracy in problems with moving boundaries that minimizes implementation complexity and allows arbitrary explicit or diagonally-implicit Runge-Kutta schemes. The approach is broadly compatible with popular PDE-specialized Runge-Kutta time integrators, including low-storage, strong stability preserving, and diagonally implicit schemes. Through numerical experiments we demonstrate that the full discretization maintains high-order spatial and temporal accuracy in the presence of complex 3D geometries and for a range of boundary conditions, including Dirichlet, Neumann, and flux conditions with large jumps in coefficients.

Meshless interface tracking for the simulation of dendrite envelope growth

The growth of dendritic grains during solidification is often modelled using the Grain Envelope Model (GEM), in which the envelope of the dendrite is an interface tracked by the Phase Field Interface Capturing (PFIC) method. In the PFIC method, an phase-field equation is solved on a fixed mesh to track the position of the envelope. While being versatile and robust, PFIC introduces certain numerical artefacts. In this work, we present an alternative approach for the solution of the GEM that employs a Meshless (sharp) Interface Tracking (MIT) formulation, which uses direct, artefact-free interface tracking. In the MIT, the envelope (interface) is defined as a moving domain boundary and the interface-tracking nodes are boundary nodes for the diffusion problem solved in the domain. To increase the accuracy of the method for the diffusion-controlled moving-boundary problem, an h-adaptive spatial discretization is used, thus, the node spacing is refined in the vicinity of the envelope. MIT combines a parametric surface reconstruction, a mesh-free discretization of the parametric surfaces and the space enclosed by them, and a high-order approximation of the partial differential operators and of the solute concentration field using radial basis functions augmented with monomials. The proposed method is demonstrated on a two-dimensional h-adaptive solution of the diffusive growth of dendrite and evaluated by comparing the results to the PFIC approach. It is shown that MIT can reproduce the results calculated with PFIC, that it is convergent and that it can capture more details in the envelope shape than PFIC with a similar spatial discretization.

Atomic-scale manipulation of polar domain boundaries in monolayer ferroelectric In2Se3

Domain boundaries have been intensively investigated in bulk ferroelectric materials and two-dimensional materials. Many methods such as electrical, mechanical and optical approaches have been utilized to probe and manipulate domain boundaries. So far most research focuses on the initial and final states of domain boundaries before and after manipulation, while the microscopic understanding of the evolution of domain boundaries remains elusive. In this paper, we report controllable manipulation of the domain boundaries in two-dimensional ferroelectric In2Se3 with atomic precision using scanning tunneling microscopy. We show that the movements of the domain boundaries can be driven by the electric field from a scanning tunneling microscope tip and proceed by the collective shifting of atoms at the domain boundaries. Our density functional theory calculations reveal the energy path and evolution of the domain boundary movement. The results provide deep insight into domain boundaries in two-dimensional ferroelectric materials and will inspire inventive applications of these materials.

Transformation Pathways of Ferromagnetic Mn-Al-Ga-Ni

This study investigates the impact of alloying Mn-Al-Ga with 3 at.-% Ni and the stability and formation mechanisms of the τ phase and the resulting magnetic properties. The stabilizing effect of Ga on the τ phase was verified, and the ternary alloy’s magnetization was measured up to M2T=482kA/m−1. The phase transformation from γ2 to τ in ternary Mn-Al-Ga was demonstrated microscopically. The solubility limit of Ni into the τ phase was exceeded at 3 at.-% and a primitive cubic κ phase formed. The Ni addition stabilized the τ phase. The highest magnetization at 2 T for the Mn52Al39.4Ga5.6Ni3 alloy was M2T=416kA/m−1
 .
 A new transformation pathway was demonstrated by first annealing the Mn-Al-Ga-Ni alloy at 800 °C for 24 h, which forms a nearly single κ phase, which is followed by a second anneal at 500 °C for 24 h at which the phase τ formed with some remaining κ phase. This is a new transformation mechanism since it involves a phase reaction from κ to τ. The energy product of the Mn-Al-Ga-Ni alloy exceeded that of the ternary Mn-Al-Ga alloy by a factor of 4.5. The κ-phase particles in the Mn-Al-Ga-Ni alloy hinder magnetic domain boundary motion, thus providing a method for magnetic hardening and increasing the energy product.

ОДНОМЕРНАЯ ДИНАМИКА ДОМЕННОЙ ГРАНИЦЫ В СЕМИСЛОЙНОЙ ФЕРРОМАГНИТНОЙ СТРУКТУРЕ

The dynamics of the domain boundary is considered using the example of a seven-layer ferromagnetic structure with three thin and four wide magnetic layers. The structure of the domain boundary is represented as a kink solution of the sine-Gordon equation. The equation of motion for magnetization was solved numerically using an explicit scheme. The discretization of the equation was carried out according to a standard five-point scheme of the "cross" type. The paper shows the features of the dynamics of the domain boundary in a multilayer magnetic system in the presence of thin magnetic layers with an increased value of the magnetic anisotropy constant. Thin layers with an increased value of the magnetic anisotropy constant compared to the homogeneous state represent potential barriers to the moving domain boundary. Thin layers with an increased magnitude of magnetic anisotropy compared to a homogeneous state represent potential barriers to a moving domain boundary. A diagram of possible scenarios of the dynamics of the domain boundary is constructed depending on the initial velocity of its movement and the distance between three thin magnetic layers. The maximum value of the kink velocity for reflection from all potential barriers, depending on their size, is obtained. With an increase in the height and width of the barrier, the value of such a threshold maximum reflection velocity of the domain boundary increases nonlinearly. With a sufficiently high barrier height, there is already an almost linear dependence on the width of this threshold velocity. With a slight increase in the speed of movement of the domain boundary, the kink can pass through the first barrier, but it is reflected from the second barrier. There is also a case of kink oscillation between the second and third potential barriers. Such fluctuations are clearly inharmonious. The dependence of the threshold velocity on the distance between the barriers is obtained. As the distance between the barriers increases, the threshold speed value tends to a value equal to the threshold speed for one barrier. In the work, the minimum value of the speed of the domain boundary of the passage of all layers, depending on the parameters of potential barriers, is obtained. It is also found that there is a critical distance separating the dynamics of the domain boundary into two regions with qualitatively different behavior of the system.

Pulsating mode in X-ray generators based on the SBN-61 crystal

Currently, pyroelectric crystals are used in the development of new portable sources of X-ray and neutron radiation. Typically, X-rays are produced when pyroelectric crystals are heated or cooled. In this work, in an X-ray generator based on a ferroelectric crystal of barium-strontium niobate Sr0.61Ba0.39Nb2O6, the pulsations of the electron and X-ray flux were registered at a constant temperature when the gas pressure increased in the range 2·10−2–10−1 Torr. The electron flux had the shape of a cross in the crystal plane. The flash duration did not exceed 0.04 seconds. The observed effect is explained by the movement of domain boundaries on the depolarized crystal face in vacuum, resulting in a large surface charge and, accordingly, an electric potential, leading to the formation of a pulsed electron flux.

Features of Internal Friction in Ferromagnets

Based on the application of two model descriptions proposed by A.A. Rodionov, it is shown that description of internal friction of magnetic materials in various magnetoelastic states subjected to alternating elastic fields should consider not only the magnetic component but also the non-magnetic component along with its changes in the presence of the magnetic field.
 The magnetic component of internal friction is associated with the movement of domain boundaries (DG) (hysteresis attenuation (amplitude-dependent — irreversible displacements of DG)) and amplitude-independent (reversible displacements of DG without separation from the fixing points) with reversible and irreversible rotations of spontaneous magnetization vectors.
 The non-magnetic component is determined by several components, all of which can dominate over a particular region of frequencies, temperatures, external influences, and initial structural states of the system under study. It depends on the type of defects, their concentrations, and spatial and orientation distribution in crystals.
 The paper proposes an approach to separate the internal friction in magnetic materials into magnetic and non-magnetic components which can be extended to materials with domains and domain boundaries including antiferromagnets, ferroelectrics, ferromagnets, etc.
 This approach leads to an expansion of the previously used ideas about the method of separating the magnetic component from the recorded spectrum of internal friction.

The Effect of Static Stress on the Anisotropy of Piezoceramics.

The influence of static compressional stress on the anisotropy of piezoelectric ceramics of BaTiO3 and PZT types is considered theoretically and experimentally. Static compression changes the domain structure of piezoceramics. These changes occur due to the reorientation of mostly 90° domain axes. As a result, all the parameters of the material change—elastic, piezoelectric, and dielectric. Some of them increase, and some, on the contrary, decrease. Changes occur in a nonlinear way, and higher-order parameters appear. The relationship between the total volume of the reoriented domains and the change in elastic moduli and piezomoduli is theoretically considered. The corresponding theoretical dependences are obtained. To confirm these theoretical dependences, experimental measurements were performed using the ultrasonic pulse-interference method at a frequency of 8 MHz. There is practically no oscillation movement of domain boundaries at this frequency, therefore, the change in the system of elastic and piezoelectric moduli is structural, not dynamic. The possibility of predicting changes in the structure of modules as a result of static compression is shown.

Study of radar absorbing characteristics of polymer composites with ferrite fillers

The search for effective radio-absorbing materials is an urgent task in solving the problems of electromagnetic compatibility, electromagnetic pollution, as well as stealth and stealth technologies. We present the results of studying the electrophysical and radio-absorbing characteristics of ferrite-polymer composites depending on the structure and magnetic properties of the ferrite filler, as well as the dielectric properties of the polymer matrix. The radio absorbing characteristics of composites F-42/Mn-Zn-ferrite, F-42/Ni-Zn-ferrite, F-42/yttrium iron garnet, F-42/BaFe12O19, F2M/LiMnZn-spinel, PS525/Mn-Zn -ferrite, PVA/Mn-Zn ferrite, and PVA/Ni-Zn ferrite have been studied. Experimental data on the reflection coefficient, determined on a metal plate in a frequency range of 0.1 – 7 GHz showed that spinel ferrites and composites containing them are effective radio absorbing materials. Analysis of the spectra of complex dielectric and magnetic permeability revealed that composites with spinel ferrites and yttrium iron garnet are characterized by a dispersion of the magnetic permeability, which arises as a result of resonance processes of the motion of domain boundaries and natural ferromagnetic resonance. Moreover, the electrical properties of ferrites can affect the high-frequency spectra of the permittivity and permeability. It is shown that the use of electroactive polymers as matrices makes it possible to increase dielectric losses in the high-frequency range and obtain the maximum attenuation of electromagnetic radiation within 25 – 40 dB with a width of 10 dB up to 2.5 GHz in 2 – 7 GHz range. The results obtained can be used in further study of the functional properties of radio-absorbing materials in the high-frequency range.

Internal friction in complex ferroelastic twin patterns

We report the first attempt to study the internal friction (IF) of complex ferroelastic twin patterns by atomistic molecular dynamics simulations. At different stress amplitudes, linear and non-linear IF regimes are observed. They are separated by a pinning/depinning threshold. At external stresses below the pinning/depinning threshold, a low linear IF background is nearly independent of temperature and configuration of the twin patterns. With increasing stresses, twin boundary motions generate non-linear anelasticity where the stress dependent IF increases to a maximum and then decays. The IF is directly related to the motion of needle twins. The effects of vacancy pinning and thermal activation are studied. The IF maximum is reduced and shifted to higher stresses by extrinsic pinning effects. The IF maximum decreases further with increasing temperature from 8 × 10−6Tc to 8 × 10−4Tc where Tc is the ferroelastic transition temperature. The non-linear IF depends by power law on the strain with exponents near 2 below the IF maximum and -1 at strains higher than the maximum. Vacancies destroy the power law and break the scale invariance of the domain boundary movements. The overall picture obtained in this study is consistent with basic experimental observations.

X-ray Flashes and Pulsating Electron Flow in X-Ray Generators Based on SBN-61 Crystals

In an X-ray generator based on a ferroelectric crystal of barium-strontium niobate Sr0.61Ba0.39Nb2O6 (SBN-61) at a temperature of about 50oC, pulsations of the electron flux and X-ray radiation were detected with an increase in gas pressure in the range 2·10-2-10-1 Torr. The electron flux had the shape of a cross in the crystal plane. The flash duration did not exceed 0.04 seconds. The pulsation period varied from 0.2 seconds at the beginning and up to 5-10 s at the end at a pressure of ~0.1 Torr. The observed effect is explained by the movement of domain boundaries on the depolarized crystal face in vacuum conditions, resulting in a large surface charge and, accordingly, an electric potential, leading to the formation of a pulsed electron flux. Keywords: X-ray radiation, electron flux, SBN-61 crystal, ferroelectric domains.

Phase domain boundary motion and memristance in gradient-doped FeRh nanopillars induced by spin injection

The B2-ordered alloy FeRh shows a metamagnetic phase transition, transforming from antiferromagnetic to ferromagnetic order at a temperature Tt∼380 K in bulk. In addition to temperature, the phase transition can be triggered by many means such as strain, chemical doping, or magnetic or electric fields. Its first-order nature means that phase coexistence is possible. Here, we show that a phase boundary in a 300-nm-diameter nanopillar, controlled by a doping gradient during film growth, is moved by an electrical current in the direction of electron flow. We attribute this to spin injection from one magnetically ordered phase region into the other driving the phase transition in a region just next to the phase boundary. The associated change in resistance of the nanopillar shows memristive properties, suggesting potential applications as memory cells or artificial synapses in neuromorphic computing schemes.

Influence of the Turing instability on the motion of domain boundaries.

Turing's theory of pattern formation has provided crucial insights into the behavior of various biological, geographical, and chemical systems over the last few decades. Existing studies have focused on moving-boundary Turing systems for which the motion of the boundary is prescribed by an external agent. In this paper, we present an extension of this theory to a class of systems in which the front motion is governed by the physical processes that occur within the domain. Biological systems exhibiting apically dominant growth and corrosion of metals and alloys highlight some of the noteworthy examples of such systems. In this study, we characterize the nature of interaction between the moving front and the Turing-instability for both an activator-inhibitor and an activator-substrate model. Behavioral regimes of periodic, as well as nonperiodic (nonconstant), growth rates are obtained. Furthermore, the trends in the first show striking similarities with the cyclic-boundary-kinetics observed in experimental systems. In general, a stationary, periodic structure is also left behind the moving front. If the periodicity of the boundary kinetics agrees with the allowed range of the stable-periodic solutions, the pattern formed tends to persist. Otherwise, it evolves to a nearby energy-minimum either by peak-splitting, peak-decay, or by settling down to a spatially homogeneous state.

Repolarization of Ferroelectric Superlattices BaZrO3/BaTiO3

With the use of the modified Sawyer-Tower scheme and Merz technique, studies were conducted on the repolarization characteristics of ferroelectric (BaZrO3/BaTiO3) superlattices on monocrystalline MgO substrate. Studies of temperature changes in the dielectric hysteresis loops indicated a sufficiently smooth decrease in spontaneous polarization compared with homogeneous barium titanate near the phase transition temperature of the superlattice. Experimental studies of switched currents have shown that the switching processes in the synthesized superlattices are implemented in two stages: activation motion (“creep” mode) and non-activation motion (slip mode). The presence of the activation switching stage and the numerical estimates show that with high probability, the movement of domain boundaries accomplishes the processes of switching in the studied superlattice. The threshold field separating the stated stages decreases with increasing temperature up to the Curie point of the superlattice, similar to the coercive field. Detection of the non-strictly exponential dependence of the switching current on the reverse field strength in the activation stage was modulated by the dependence with the power-law exponent for the applied electric field. Both techniques indicate that the studied superlattices have a small internal displacement field directed from the superlattice to the substrate.

Investigation of the mechanism of domain switching in different Na0.5Bi0.5TiO3 microstructures

Abstract Several researches have studied the physical properties of hydrothermally-synthesized low dimensional piezoelectric nanostructures. However, the obtained piezoelectric coefficient is not high and the relationship between physical properties and microstructures is still neglected. Here we report the piezoelectric and ferroelectric properties of different lead-free sodium bismuth titanate (Na0.5Bi0.5TiO3, NBT) microstructures synthesised with hydrothermal routes and give visualization of domain structures using piezoresponse force microscopy. The NBT nanowire exhibits better local piezoelectric response compared with NBT spherical aggregates and microcubes and other one-dimensional materials prepared by hydrothermal method and the large piezoelectric coefficient of nanowire was explained by observed regular stripe domain structures. Moreover, it is found that there are different domain configurations at the top and side of the nanowire under the external electrical fields, which don't change the regular stripe domain structure but lead to the movement of domain boundaries. By finite element modeling, it attributes to the different electric potential distributions from tip within the nanowire.

DYNAMICS OF VIBRA AMICS OF VIBRATIONAL MOTION OF THE DOM TION OF THE DOMAIN BORDER AIN BORDER IN THE FERRITE GRADE OF Tb3Fe5O12

The magneto-optical method is used to study the dynamics of the oscillatory motion of domain boundaries in a Tb3Fe5O12 garnet ferrite in the temperature range 200-295K, including the magnetic compensation point of this ferrimagnet Fs ≈ 249K. To interpret the experimental results obtained, a theoretical model of magnetic resonance of domain boundaries is proposed, according to which when the temperature approaches the compensation point, the mass of the domain boundaries tends to infinity, and the resonance frequency tends to zero

Effects of poling and crystallinity on the dielectric properties of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 at cryogenic temperatures

The mechanisms underlying the anomalously large, room temperature piezoelectric activity of relaxor-PbTiO3 type single crystals have previously been linked to low temperature relaxations in the piezoelectric and dielectric properties. We investigate the properties of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 between 10 and 300 K using dielectric permittivity measurements. We compare results on single crystal plates measured in the [001] and [111] directions with a polycrystalline ceramic of the same composition. Poled crystals have very different behaviour to unpoled crystals, whereas the dielectric spectrum of the polycrystalline ceramic changes very little on poling. A large, frequency dependent dielectric relaxation is seen in the poled [001] crystal around 100 K. The relaxation is much less prominent in the [111] cut crystal, and is not present in the polycrystalline ceramic. The unique presence of the large relaxation in poled, [001] oriented crystals indicates that the phenomenon is not due their relaxor nature alone. We propose that heterophase dynamics such as the motion of phase domain boundaries are responsible for both the anomalous electromechanical and dielectric behaviour.

Direct Microscopic Observation of Domain Rearrangement Mechanism of Photo-Orientation Process in Azobenzene-Containing Materials.

The evolution of the domain structure of two azobenzene-containing materials during irradiation with polarized light was monitored using polarized optical microscopy with additional λ-waveplate for discerning the domains oriented parallel and perpendicular to irradiating light polarization. It is shown that the process of photo-orientation consists in growth of perpendicularly oriented domains and diminishing of parallel domains via the movement of domain boundaries. These data confirm the mechanism of photo-orientation via domain structure rearrangement.

Visualization of Dynamic Vortex Structures in Magnetic Films with Uniaxial Anisotropy (Micromagnetic Simulation)

Three-dimensional computer simulation of dynamic processes in a moving domain boundary separating domains in a soft magnetic uniaxial film with planar anisotropy is performed by numerical solution of Landau-Lifshitz-Gilbert equations. The developed visualization methods are used to establish the connection between the motion of surface vortices and antivortices, singular (Bloch) points, and core lines of intrafilm vortex structures. A relation between the character of magnetization dynamics and the film thickness is found. The analytical models of spatial vortex structures for imitation of topological properties of the structures observed in micromagnetic simulation are constructed.

Current-Driven Motion of Domain Boundaries between Skyrmion Lattice and Helical Magnetic Structure.

To utilize magnetic skyrmions, nanoscale vortex-like magnetic structures, experimental elucidation of their dynamics against current application in various circumstances such as in confined structure and mixture of different magnetic phases is indispensable. Here, we investigate the current-induced dynamics of the coexistence state of magnetic skyrmions and helical magnetic structure in a thin plate of B20-type helimagnet FeGe in terms of in situ real-space observation using Lorentz transmission electron microscopy. Current pulses with various heights and widths were applied, and the change of the magnetic domain distribution was analyzed using a machine-learning technique. The observed average driving direction of the two-magnetic-state domain boundary is opposite to the applied electric current, indicating ferromagnetic s-d exchange coupling in the spin-transfer torque mechanism. The evaluated driving distance tends to increase with increasing the pulse duration time, current density (>1 × 109 A/m2), and sample temperature, providing valuable information about hitherto unknown current-induced dynamics of the skyrmion-lattice ensemble.