A model of elastic and relaxation polarization of ferroelectrics with a distribution of domain walls over relaxation times and natural frequencies

2009 ◽  
Vol 51 (7) ◽  
pp. 1503-1506 ◽  
Author(s):  
V. F. Tilles ◽  
A. M. Metal’nikov ◽  
R. M. Pecherskaya
Keyword(s):  
Domain Walls ◽  
Natural Frequencies ◽  
Relaxation Times ◽  
Relaxation Polarization

Relaxation Polarization Dependence of Circular Vector Gratings in Azobenzene Glassy Molecular Films

2020 ◽  
Vol 850 ◽  
pp. 285-290
Author(s):  
Andris Ozols ◽  
Peteris Augustovs ◽  
Kaspars Traskovskis ◽  
Valdis Kokars ◽  
Lauma Laipniece ◽  
...  
Keyword(s):  
Diffraction Efficiency ◽  
Relaxation Times ◽  
Grating Period ◽  
Volume Density ◽  
Laser Beams ◽  
Relaxation Polarization ◽  
Polarized Beam ◽  
Sandwich Type ◽  
Phd Thesis ◽  
532 Nm

Holographic grating recording and relaxation is studied in different azobenzene molecular glassy films by circularly orthogonally polarized 532 nm laser beams L and R. The readout was made by circularly polarized (R or L) 632.8 nm laser beam. Sandwich-type samples (glass-film-glass) were also studied. Maximum diffraction efficiency of 81% has been achieved in sandwich-type AR-173 film. The following relaxation features have been found: after reaching diffraction efficiency (DE) maximum no DE decay took place; DE read out by R-polarized beam was always higher than that by L-polarized beam; in sandwich-type samples DE decayed until zero when read out by R-polarization whereas DE was zero when read out by L-polarization. 50% relaxation times varied from 4 to 44 minutes, and they mainly decreased when grating period was increased. The observed relaxation peculiarities can be understood if one assumes that volume birefringence grating (VBG) is recorded followed by volume density grating (VDG) and surface relief grating (SRG) recording. R-polarization "feels" all gratings whereas L-polarization only VDG and SRG. At large exposures VDG and SRG dominate. These results confirm the conclusion made by J.Mikelsone in her 2018 PhD thesis that birefringence grating recording in azobenzene materials is a neccessary condition for SRG appearance.

scholarly journals Current-Driven Domain Wall Motion in Curved Ferrimagnetic Strips Above and Below the Angular Momentum Compensation

2021 ◽  
Vol 9 ◽  
Author(s):  
D. Osuna Ruiz ◽  
O. Alejos ◽  
V. Raposo ◽  
E. Martínez
Keyword(s):  
Angular Momentum ◽  
Domain Wall ◽  
High Speed ◽  
Wall Motion ◽  
Domain Walls ◽  
Relaxation Times ◽  
Domain Wall Motion ◽  
Current Density Distribution ◽  
Terminal Velocity ◽  
Artificial System

Current driven domain wall motion in curved Heavy Metal/Ferrimagnetic/Oxide multilayer strips is investigated using systematic micromagnetic simulations which account for spin-orbit coupling phenomena. Domain wall velocity and characteristic relaxation times are studied as functions of the geometry, curvature and width of the strip, at and out of the angular momentum compensation. Results show that domain walls can propagate faster and without a significant distortion in such strips in contrast to their ferromagnetic counterparts. Using an artificial system based on a straight strip with an equivalent current density distribution, we can discern its influence on the wall terminal velocity, as part of a more general geometrical influence due to the curved shape. Curved and narrow ferrimagnetic strips are promising candidates for designing high speed and fast response spintronic circuitry based on current-driven domain wall motion.

Acoustic attenuation in ferroelectric Sn2P2S6 crystals

Open Physics ◽  
2010 ◽  
Vol 8 (6) ◽  
Author(s):  
Anton Kohutych ◽  
Ruslan Yevych ◽  
Sergij Perechinskii ◽  
Yulian Vysochanskii
Keyword(s):  
Relaxation Time ◽  
Domain Walls ◽  
Ferroelectric Phase ◽  
Relaxation Times ◽  
Sound Attenuation ◽  
Acoustic Attenuation ◽  
Brillouin Spectroscopy ◽  
Velocity Anomaly ◽  
Uniaxial Ferroelectric ◽  
Quantitative Calculations

AbstractThe temperature and frequency dependencies of sound attenuation for the proper uniaxial ferroelectric Sn2P2S6, which has a strong nonlinear interaction of the polar soft optic and fully symmetrical optic modes that is related to the triple well potential, were studied by Brillouin spectroscopy. It was found that the sound velocity anomaly is described in the Landau-Khalatnikov approximation with one relaxation time. For explanation of the observed temperature and frequency dependencies of the sound attenuation in the ferroelectrric phase, the accounting of several relaxation times is needed and, for quantitative calculations, the mode Gruneisen coefficients are more appropriate as interacting parameters than are the electrostrictive coefficients. Relaxational sound attenuation by domain walls also appears in the ferroelectric phase of Sn2P2S6 crystals.

Magnetic Studies on the 1-D Antiferromagnetic Chains of enH2Mn(Fe)F5

1995 ◽  
Vol 50 (11) ◽  
pp. 1627-1637 ◽  
Author(s):  
C. Frommen ◽  
L. Schröder ◽  
U. Bentrup ◽  
W. Massa ◽  
J. Pebler
Keyword(s):  
Domain Walls ◽  
Relaxation Times ◽  
Magnetic Ordering ◽  
Thermal Excitation ◽  
Magnetic Studies ◽  
Local Anisotropy ◽  
Magnetic Susceptibilities ◽  
Relaxation Effects ◽  
Exponential Temperature Dependence ◽  
Moving Domain

Measurements of the 57Fe Mössbauer effect and of magnetic susceptibilities have been performed on the 57Fe doped or pure quasi-1-d antiferromagnetic chain compound enH2MnF5 as a function of temperature. Particular attention was paid to the regions very near the Néel point at TN = 14.5(5) K. The Mössbauer spectra fitted by the Blume-Tjon model show definite relaxation effects, which are attributed to short-range order with temperature-dependent relaxation times. The soliton model of non-linear excitations was applied. Experimental data confirm the predicted exponential temperature dependence of the thermal excitation of moving domain walls. From the activation energy EA/k = 184(5) K and the 1-d exchange energy J/k = -13.6(2) K a local anisotropy energy D/k of -2.4 (3) K was obtained which is smaller than D/k = -3.5 K derived from our single crystal measurements of magnetic susceptibilities. Within the 3-d magnetic ordering the interchain interaction amounts to J′/k ≈ 0.22(4) K (J′/J = 15.8 10-3). A zero-spin reduction ⊿S/S equal to 17% was obtained. 1-d correlations are observed for TN<T< |J|S (S + 1)/k ≈ 78 K, and a crystallographic phase transition at 216 K was indicated in the magnetic properties as well as by DSC and X-ray powder diffraction measurements.

scholarly journals Импедансные характеристики γ-облученных твердых растворов (TlGaSe-=SUB=-2-=/SUB=-)-=SUB=-1-x-=/SUB=-(TlInS-=SUB=-2-=/SUB=-)-=SUB=-x-=/SUB=-

2020 ◽  
Vol 54 (6) ◽  
pp. 511
Author(s):  
Р.М. Сардарлы ◽  
Ф.Т. Салманов ◽  
Н.А. Алиева ◽  
Р.М. Аббаслы
Keyword(s):  
Electrical Conductivity ◽  
Ionic Conductivity ◽  
Solid Solutions ◽  
Relaxation Times ◽  
Dissipation Factor ◽  
Localized States ◽  
Frequency Range ◽  
Γ Irradiation ◽  
Relaxation Polarization ◽  
Before And After

Abstract Charge transport in (TlGaSe_2)_1 –_ x (TlInS_2)_ x solid solutions in the frequency range of 20–10^6 Hz before and after γ irradiation is studied using impedance-spectroscopy methods. The relaxation character of the permittivity dispersion and the nature of the dielectric loss are established. The frequency dependence of the dissipation factor tanδ in the crystals of the (TlGaSe_2)_1 –_ x (TlInS_2)_ x solid solutions is caused not only by relaxation polarization, but also by reach-through conductivity. The relaxation times are found to be τ = 10^–3 s. It is determined that, in the frequency range of 10^5–5 × 10^5 Hz, the electrical conductivity obeys the regularity σ ~ f ^ S (0.1 ≤ S ≤ 1.0), which is indicative of the conductivity over localized states. It is shown that a further increase in the frequency leads to an increase in the ionic conductivity and transition of the system to the superionic state.

The direct determination of magnetic domain wall profiles using a split detector STEM

1978 ◽  
Vol 36 (1) ◽  
pp. 466-467
Author(s):  
J.N. Chapman ◽  
P.E. Batson ◽  
E.M. Waddell ◽  
R.P. Ferrier
Keyword(s):  
Electron Microscope ◽  
Domain Wall ◽  
Transmission Electron Microscope ◽  
Domain Walls ◽  
Photographic Plate ◽  
Magnetic Domain ◽  
Direct Determination ◽  
Quantitative Information ◽  
Scanning Transmission Electron Microscope ◽  
Transmission Electron

By far the most commonly used mode of Lorentz microscopy in the examination of ferromagnetic thin films is the Fresnel or defocus mode. Use of this mode in the conventional transmission electron microscope (CTEM) is straightforward and immediately reveals the existence of all domain walls present. However, if such quantitative information as the domain wall profile is required, the technique suffers from several disadvantages. These include the inability to directly observe fine image detail on the viewing screen because of the stringent illumination coherence requirements, the difficulty of accurately translating part of a photographic plate into quantitative electron intensity data, and, perhaps most severe, the difficulty of interpreting this data. One solution to the first-named problem is to use a CTEM equipped with a field emission gun (FEG) (Inoue, Harada and Yamamoto 1977) whilst a second is to use the equivalent mode of image formation in a scanning transmission electron microscope (STEM) (Chapman, Batson, Waddell, Ferrier and Craven 1977), a technique which largely overcomes the second-named problem as well.

Lorentz microscopy study of magnetic domain walls in Fe-Cr-Co alloys

1978 ◽  
Vol 36 (1) ◽  
pp. 462-463
Author(s):  
Yalcin Belli
Keyword(s):  
Domain Walls ◽  
Magnetic Domain ◽  
Microscopy Study ◽  
Ferromagnetic Phase ◽  
Stable Phase ◽  
Magnetic Domains ◽  
Lorentz Microscopy ◽  
Magnetic Hardening ◽  
Electron Microscopes ◽  
Co Alloys

Fe-Cr-Co alloys have great technological potential to replace Alnico alloys as hard magnets. The relationship between the microstructures and the magnetic properties has been recently established for some of these alloys. The magnetic hardening has been attributed to the decomposition of the high temperature stable phase (α) into an elongated Fe-rich ferromagnetic phase (α1) and a weakly magnetic or non-magnetic Cr-rich phase (α2). The relationships between magnetic domains and domain walls and these different phases are yet to be understood. The TEM has been used to ascertain the mechanism of magnetic hardening for the first time in these alloys. The present paper describes the magnetic domain structure and the magnetization reversal processes in some of these multiphase materials. Microstructures to change properties resulting from, (i) isothermal aging, (ii) thermomagnetic treatment (TMT) and (iii) TMT + stepaging have been chosen for this investigation. The Jem-7A and Philips EM-301 transmission electron microscopes operating at 100 kV have been used for the Lorentz microscopy study of the magnetic domains and their interactions with the finely dispersed precipitate phases.

An emerging technology: Nuclear magnetic resonance microscopy

1988 ◽  
Vol 46 ◽  
pp. 1000-1001
Author(s):  
M.J. Hennessy ◽  
E. Kwok
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Relaxation Times ◽  
Basic Research ◽  
Local Environment ◽  
Magnetic Resonance Images ◽  
Nmr Microscopy ◽  
Mri Scans ◽  
Temperature Relaxation ◽  
Nuclear Magnetic

Much progress in nuclear magnetic resonance microscope has been made in the last few years as a result of improved instrumentation and techniques being made available through basic research in magnetic resonance imaging (MRI) technologies for medicine. Nuclear magnetic resonance (NMR) was first observed in the hydrogen nucleus in water by Bloch, Purcell and Pound over 40 years ago. Today, in medicine, virtually all commercial MRI scans are made of water bound in tissue. This is also true for NMR microscopy, which has focussed mainly on biological applications. The reason water is the favored molecule for NMR is because water is,the most abundant molecule in biology. It is also the most NMR sensitive having the largest nuclear magnetic moment and having reasonable room temperature relaxation times (from 10 ms to 3 sec). The contrast seen in magnetic resonance images is due mostly to distribution of water relaxation times in sample which are extremely sensitive to the local environment.

Temperature Dependence of Magnetic Domains and Wall Structures

1972 ◽  
Vol 30 ◽  
pp. 496-497
Author(s):  
Sonoko Tsukahara ◽  
Tadami Taoka ◽  
Hisao Nishizawa
Keyword(s):  
Temperature Dependence ◽  
Domain Walls ◽  
Magnetic Domain ◽  
Iron Film ◽  
Objective Lens ◽  
Lorentz Microscopy ◽  
Domain Structures ◽  
Wall Structures ◽  
Crystal Films ◽  
Metallurgical Structure

The high voltage Lorentz microscopy was successfully used to observe changes with temperature; of domain structures and metallurgical structures in an iron film set on the hot stage combined with a goniometer. The microscope used was the JEM-1000 EM which was operated with the objective lens current cut off to eliminate the magnetic field in the specimen position. Single crystal films with an (001) plane were prepared by the epitaxial growth of evaporated iron on a cleaved (001) plane of a rocksalt substrate. They had a uniform thickness from 1000 to 7000 Å.The figure shows the temperature dependence of magnetic domain structure with its corresponding deflection pattern and metallurgical structure observed in a 4500 Å iron film. In general, with increase of temperature, the straight domain walls decrease in their width (at 400°C), curve in an iregular shape (600°C) and then vanish (790°C). The ripple structures with cross-tie walls are observed below the Curie temperature.

Imaging of ferroelectric domain walls by electron holography

1992 ◽  
Vol 50 (1) ◽  
pp. 246-247
Author(s):  
Xiao Zhang
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Domain Walls ◽  
Ferroelectric Domain ◽  
Object Wave ◽  
Electron Holography ◽  
High Resolution Imaging ◽  
Quantitative Measurements ◽  
Resolution Imaging ◽  
Electron Microscopes

Electron holography has recently been available to modern electron microscopy labs with the development of field emission electron microscopes. The unique advantage of recording both amplitude and phase of the object wave makes electron holography a effective tool to study electron optical phase objects. The visibility of the phase shifts of the object wave makes it possible to directly image the distributions of an electric or a magnetic field at high resolution. This work presents preliminary results of first high resolution imaging of ferroelectric domain walls by electron holography in BaTiO3 and quantitative measurements of electrostatic field distribution across domain walls.

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