Domain Structure Dynamics Research Articles

Fractal model of polarization switching kinetics in ferroelectrics under nonequilibrium conditions of electron irradiation

The paper presents the results of the fractal and multifractal analysis of polarization switching current in ferroelectrics under electron irradiation, which allows statistical memory effects to be estimated at dynamics of domain structure. The mathematical model of formation of electron beam-induced polarization current in ferroelectrics was suggested taking into account the fractal nature of domain structure dynamics. In order to realize the model the computational scheme was constructed using the numerical solution approximation of fractional differential equation. Evidences of electron beam-induced polarization switching process in ferroelectrics were specified at a variation of control model parameters.

Direct observation of magnetization reversal of hot-deformed Nd-Fe-B magnet

The dynamic magnetic domain structure in magnetization and demagnetization process of hot-deformed and NdCu-diffused Nd2Fe14B magnets were in-situ observed by Lorentz transmission electron microscopy (LTEM). The demagnetization process of hot-deformed sample is dominated by domain-wall pinning, while that of NdCu-diffused sample is mainly the magnetization reversal of single grains or grain aggregations. This firstly observed result gives an explicit evidence to understand the coercivity mechanism of magnetically segregated magnet. The effect of magnetic field of TEM on decrease in domain wall energy was theoretically analyzed, which helps to understand the in-situ observation process of magnetic materials.

Dielectric losses in the triglycine sulfate crystal under heating and cooling

Temperature dynamics of the dielectric spectra and domain structure in the triglycine sulfate (TGS) hydrogen-containing ferroelectric under heating and cooling has been studied using the dielectric spectroscopy and atomic-force microscopy methods. The dielectric spectra are analyzed by the temperature-frequency dependences of the losses e″ and by the temperature behavior of the maximum losses e″max in the dispersion region at frequencies ranging from 102 to 106 Hz. A dynamic conductivity model is proposed for calculating temperature dependences of losses e″max. The domain structure dynamics during the heating and cooling of the TGS crystal near the phase transition is studied using the in situ piezoresponse force microscopy. It is experimentally and theoretically shown that the relaxation dispersion is governed by the binding of strongly correlated dipoles with the main lattice that serves as a thermostat.

Temperature dynamics of triglycine sulfate domain structure according to atomic force microscopy and dielectric spectroscopy data

A hydrogen-containing ferroelectric triglycine sulfate (TGS) was comprehensively studied with an atomic force microscopy (AFM) and dielectric spectroscopy. The domain structure dynamics was in situ investigated with piezoresponse force microscopy (PFM) during heating and cooling the TGS crystal near phase transition. Relaxation dependencies of domain boundaries general perimeter and domain dimensions were obtained. TGS dielectric spectra measured at the frequency range from 10 to 1011 Hz were analyzed on basis of significant contribution of conductivity into the dielectric response of ferroelectrics and a good agreement with the experimental data was received. It allows us to obtain more information about temperature dynamics of the domain structure.

Domain imaging in ferroelectric thin films via channeling-contrast backscattered electron microscopy

Ferroelastic domain walls provide opportunities for deterministically controlling mechanical, optical, electrical, and thermal energy. Domain wall characterization in micro- and nanoscale systems, where their spacing may be of the order of 100 nm or less is presently limited to only a few techniques, such as piezoresponse force microscopy and transmission electron microscopy. These respective techniques cannot, however, independently characterize domain polarization orientation and domain wall motion in technologically relevant capacitor structures or in a non-destructive manner, thus presenting a limitation of their utility. In this work, we show how backscatter scanning electron microscopy utilizing channeling contrast yield can image the ferroelastic domain structure of ferroelectric films with domain wall spacing as narrow as 10 nm. Combined with electron backscatter diffraction to identify grain orientations, this technique provides information on domain orientation and domain wall type that cannot be readily measured using conventional non-destructive methods. In addition to grain orientation identification, this technique enables dynamic domain structure changes to be observed in functioning capacitors utilizing electrodes that are transparent to the high-energy backscattered electrons. This non-destructive, high-resolution domain imaging technique is applicable to a wide variety of ferroelectric thin films and a multitude of material systems where nanometer-scale crystallographic twin characterization is required.

Polarization Switching Response and Domain Structure Dynamics Induced in Ferroelectrics by Incident Electron Beams

The article is devoted to the analysis of polarization reversal process arising in ferroelectrics under electron beam exposure. The advanced model was proposed to describe the polarization switching process in ferroelectrics as well as formation of polarization switching response in electron beam-induced polarization current mode of SEM taking into account the specific character of domain structure dynamics. Simulation of polarization switching current in TGS ferroelectric crystals was performed to estimate the main characteristics of electron beam-induced polarization reversal processes.

Multiferroic materials and magnetoelectric physics: symmetry, entanglement, excitation, and topology

Multiferroics are those materials with more than one ferroic order, and magnetoelectricity refers to the mutual coupling between magnetism and electricity. The discipline of multiferroicity has never been so highly active as that in the first decade of the twenty-first century, and it has become one of the hottest disciplines of condensed matter physics and materials science. A series of milestones and steady progress in the past decade have enabled our understanding of multiferroic physics substantially comprehensive and profound, which is further pushing forward the research frontier of this exciting area. The availability of more multiferroic materials and improved magnetoelectric performance are approaching to make the applications within reach. While seminal review articles covering the major progress before 2010 are available, an updated review addressing the new achievements since that time becomes imperative. In this review, following a concise outline of the basic knowledge of multiferroicity and magnetoelectricity, we summarize the important research activities on multiferroics, especially magnetoelectricity and related physics in the last six years. We consider not only single-phase multiferroics but also multiferroic heterostructures. We address the physical mechanisms regarding magnetoelectric coupling so that the backbone of this divergent discipline can be highlighted. A series of issues on lattice symmetry, magnetic ordering, ferroelectricity generation, electromagnon excitations, multiferroic domain structure and domain wall dynamics, and interfacial coupling in multiferroic heterostructures, will be revisited in an updated framework of physics. In addition, several emergent phenomena and related physics, including magnetic skyrmions and generic topological structures associated with magnetoelectricity will be discussed.

Frequency dependence of the domain-structure dynamics of Fe–3% Si crystals in rotating magnetic fields

Features of the behavior of the domain structure of Fe–3% Si single crystals that are subjected to magnetization reversal in rotating magnetic fields in the range of frequencies f = 20–250 Hz and induction amplitudes B m = 0.25–1.5 T have been investigated. It has been found that, as the rotation frequency of the field increases, the volume of the sample subjected to magnetization reversal through the displacement of 90° domain walls of internal C domains grows continuously. The observed rearrangement of the domain structure made it possible to qualitatively explain features of changes in the frequency behavior of magnetic losses upon rotational magnetization reversal of the samples in the induction range under study.

The nucleoid as a smart polymer.

The nucleoid as a smart polymer.

Experimental and Theoretical Study of Stripe Magnetic Domain Structure Drift in Iron Garnet Crystals

The results of experimental and theoretical study of magnetic domain structure drift in low frequency oscillating magnetic eld oriented perpendicular to the sample plate are presented. Experimental study was performed on uniaxial iron garnet (TbErGd)3(FeAl)5O12 (111) plate with rhombic anisotropy for the case when orientation of domain walls of stripe domains is preserved. Dynamic domain structure was revealed by means of magnetooptic Faraday e ect and registered by high speed digital camera at the speed equal to 1200 fps. Theoretical model based on the motion equations for coupled harmonic oscillators that takes into account attenuation and eld inhomogeneity along the plate is proposed.

Effect of temperature on the formation of dynamic magnetic domains in ferrite-garnet films

Dynamic domain structures in ferrite-garnet films (111) with normal anisotropy are investigated for the temperature range of 77–300 K. The boundaries of the area of the existence of one- and two-armed spiral domains are determined as a function of the temperature, frequency, and amplitude of the vertical field. It is found that the region of the existence of spiral dynamic domains shift toward low frequencies when the temperature is reduced.

Stress-Induced Changes in Closure Domain Structure Dynamics in Bistable Ferromagnetic Microwire

A new experimental method for the study of closure domain structure dynamics in bistable ferromagnetic microwires is proposed. The simple experimental set-up enables detection of the presence of a free domain wall in the wire after application of a well-de ned rectangular magnetic eld pulse. The changes in closure domain structure dynamics, caused by applied tensile stress, are demonstrated by measurements on Fe77.5B15Si7.5 glasscoated microwire. Minimum critical eld for the release of a domain wall from the closure domain structure increases with increasing stress, while on the other hand, the minimum time needed for this process rapidly decreases with increasing stress.

Kinetics of 90° domain wall motions and high frequency mesoscopic dielectric response in strained ferroelectrics: a phase-field simulation.

The dielectric and ferroelectric behaviors of a ferroelectric are substantially determined by its domain structure and domain wall dynamics at mesoscopic level. A relationship between the domain walls and high frequency mesoscopic dielectric response is highly appreciated for high frequency applications of ferroelectrics. In this work we investigate the low electric field driven motion of 90°-domain walls and the frequency-domain spectrum of dielectric permittivity in normally strained ferroelectric lattice using the phase-field simulations. It is revealed that, the high-frequency dielectric permittivity is spatially inhomogeneous and reaches the highest value on the 90°-domain walls. A tensile strain favors the parallel domains but suppresses the kinetics of the 90° domain wall motion driven by electric field, while the compressive strain results in the opposite behaviors. The physics underlying the wall motions and thus the dielectric response is associated with the long-range elastic energy. The major contribution to the dielectric response is from the polarization fluctuations on the 90°-domain walls, which are more mobile than those inside the domains. The relevance of the simulated results wth recent experiments is discussed.

A device for the recording of the dynamic domain structure of ferromagnets in rotating magnetic fields

The principle of operation of a device for the observation and recording of the type of domain structure (DS) of ferromagnets that are remagnetized in rotating magnetic fields is described. This makes it possible to reliably fix the type of the domain structure of a ferromagnet under single cycles of magnetization reversal in the frequency range of 20–400 Hz and in the induction interval of 0.25–2.0 T. The observed features of the rearrangement of the DS in the samples of anisotropic electrotechnical steel allowed us to find a method for reducing the level of its magnetic losses in rotating magnetic fields and thus to improve its performance characteristics significantly.

Drift of domain walls in a harmonic magnetic field

It is shown that a two-step form of the dynamic magnetization curve (and the hysteresis loop) established for a multiaxial ferrite-garnet wafer with a low quality factor (Q < 1) and considerable anisotropy in the plane (K p /K u = 14) in the frequency range of 25–1000 Hz is explained by the reconstruction of the dynamic domain structure, particularly by the established features of the drift of domain boundaries in the harmonic magnetic field.

Dynamics of closure domain structure in bistable ferromagnetic microwire

Dynamics of closure domain structure in bistable glass-coated Fe77.5B15Si7.5 amorphous ferromagnetic microwire was studied experimentally and theoretically. A new experiment for this study was proposed. The basic idea of this consisted in checking whether a well-defined rectangular magnetic field pulse applied to the microwire end can produce a stable and free domain wall in the microwire. A theoretical model previously used for describing the wall depinning process from the wire end was adapted for interpretation of our experimental results. Information about parameters of the potential well in which the wall is initially trapped as well as about wall dynamics was obtained. Values of these parameters are in good agreement with those obtained from different types of experiments.

Temperature dependence of polarization switching in deuterated glycine phosphite single crystals

The influence of temperature on domain switching behaviour has been investigated in deuterated glycine phosphite (DGPI) single crystals. The experimental data have been collected from direct microscopic observation of the domain structure during switching and D–E hysteresis loop registration. In order to clarify the relationship between macroscopic hysteresis loop and local switching parameters, we used the nematic liquid crystal method to visualize domain structure dynamics in electric fields. The ‘triple-like’ shape of hysteresis loop observed near the ferro- to paraelectric phase transition has a strong link to the configuration of ferroelectric microdomains and compositional disorder in DGPI crystals.

AFM investigation of the mechanism for microwave effect on ferroelectric triglycine sulfate

Relation between the microwave effect on ferroelectric triglycine sulfate and the crystal structure dynamics is studied within the concept of ferroactive medium evolution. It is shown that the effect is most distinct in defect-free samples and correlates with the domain structure dynamics. Domain walls are considered to be responsible for structure-sensitive characteristics of triglycine sulfate.

Comparison of polarization switching in ferroelectric TGS and relaxor SBN crystals

The comparative experimental analysis of polarization reversal kinetics in conventional homogeneous triglycine sulfate ((NH_{2}CH_{2}COOH)_{3} \cdot H_{2}SO_{4}; TGS) and relaxor strontium barium niobate (Sr_{0.61}Ba_{0.39}Nb_{2}O_{6}; SBN) crystals have been performed in a broad range of measurement conditions. The experimental data have been collected from microscopic observation of the domain structure, switching current and D-E hysteresis loop registration. The hysteresis loop and dielectric spectra have a strong link to the configuration of ferroelectric microdomains. The domain structure dynamics was examined by the nematic liquid crystal (NLC) method.

Study of Nanoscale Domain Structure and Elastic Response of Lead-Free Piezoelectric Ceramics by Scanning Probe Microscopy

The nanoscale domain structure and variation of local elasticity in lead-free piezoelectric ceramics were investigated using home-made piezoresponse force microscope (PFM) and low-frequency scanning probe acoustic microscope (SPAM) based on a commercial atomic force microscope. The static domain structure and domain dynamics during polarization reversal were studied by PFM, while SPAM investigations showed the elastic and subsurface ferroelectrics structures. PFM and SPAM provided powerful tools for measurements of the local electromechanical and elastic properties of lead-free piezoelectric ceramics.