Reversible Domain Wall Motion Research Articles

Research on optimized piezoelectric properties of PNN-PMN-PT ceramics and corresponding underlying factors based on component regulation

To meet the increasing demands for developing miniaturized high-precision modern piezoelectric devices, researchers are focusing their attention on PbTiO3 (PT) relaxor ferroelectrics having excellent comprehensive performance. Although the partial substitution of Pb(Mg1/3Nb2/3)O3 (PMN)-PT with Pb(Ni1/3Nb2/3)O3 (PNN)-PT has been reported to improve dielectric and piezoelectric properties, the factors underlying the performance improvement of the PNN-PMN-PT ternary system remain unclear. Therefore, based on PT content regulation, the 0.128PNN-(0.872-x)PMN-xPT (x = 0.316, 0.326, 0.336, 0.346, and 0.356) ternary ceramics were fabricated, and the crystal structure and electrical properties were systematically investigated during the rhombohedral-tetragonal phase transition. The 0.128PNN-0.536PMN-0.336PT composition exhibited optimum performance with the piezoelectric charge coefficient, effective piezoelectric strain coefficient, dielectric constant were 691 pC/N, 1060 pm/V and 4545 respectively at a maximum permittivity temperature of 136 ℃, signifying its potential for use in transducers and actuators. The outstanding properties of this system were mainly derived from the lattice distortion and reversible domain wall motion. The results indicated that the multiphase coexistence and enhanced B-site disorder in the perovskite structure contribute to the improvement in the piezoelectric properties, which would facilitate the design and development of novel piezoelectric materials.

Current-driven writing process in antiferromagnetic Mn2Au for memory applications

Current pulse driven Néel vector rotation in metallic antiferromagnets is one of the most promising concepts in antiferromagnetic spintronics. We show microscopically that the Néel vector of epitaxial thin films of the prototypical compound Mn2Au can be reoriented reversibly in the complete area of cross shaped device structures using single current pulses. The resulting domain pattern with aligned staggered magnetization is long term stable enabling memory applications. We achieve this switching with low heating of ≈20 K, which is promising regarding fast and efficient devices without the need for thermal activation. Current polarity dependent reversible domain wall motion demonstrates a Néel spin-orbit torque acting on the domain walls.

Enhancing Electromechanical Properties of PZT-Based Piezoelectric Ceramics by High-Temperature Poling for High-Power Applications.

Defect engineering is a proven method to tune the properties of perovskite oxides. In demanding high-power piezoelectric ceramic applications, acceptor doping is the most effective method to harden ceramics, but it inevitably degrades the ceramics' electromechanical properties. Herein, a poling method based on acceptor doping, namely, high-temperature poling, is implemented by applying an electric field above the Curie temperature for poling to achieve a balance of the properties of piezoelectric coefficient d33 and mechanical quality factor Qm. After high-temperature poling, the piezoelectric property of 0.6 mol % Mn-doped Pb0.92Sr0.08(Zr0.533Ti0.443Nb0.024)O3 is d33 = 483 pC/N and Qm = 448. Compared with the traditional poling, the piezoelectric coefficient d33 of the high-temperature poling ceramics increased by approximately 40%, and Qm also increased by nearly 18%. Therefore, high d33 and Qm were exhibited by our PZT piezoelectric ceramics. Rayleigh's law analysis, XRD, and transmission electron microscopy analysis show that, after high-temperature poling, the considerably increased d33 is related to the large increase in the reversible domain wall motion in the intrinsic effect, while the slightly increased Qm is related to the inhibited irreversible domain wall motion in the extrinsic effect. This study reports a method for high-temperature poling and provides insights into the design of high-power piezoelectric ceramics with high d33 and Qm.

Enhanced electric-field-induced strains in (K,Na)NbO3 piezoelectrics from heterogeneous structures

Piezoelectrics exhibit mechanical strain in response to electrical stimuli and vice versa. A high level of electric-field-induced strain with minimal hysteresis is desired for piezoelectric materials when used as actuators. The past two decades have seen extensive research into lead-free piezoelectrics to replace Pb(Zr,Ti)O3 and compositional engineering has been demonstrated to be an effective method to tailor their functional properties. Doped (K,Na)NbO3 (KNN) compositions with elaborate compositional tuning can exhibit enhanced electromechanical properties. However, a balance between enhanced properties and non-toxicity of the dopants should be considered. In this work, we propose to use microstructural engineering to enhance the properties. Based on phase-field simulations, we propose to take advantage of depolarization energies generated by polar-nonpolar interfaces, to increase the contribution of domain wall motion to electric-field-induced strain. Heterogeneous ferroelectric-paraelectric microstructures were introduced into a KNN ceramic via a two-step sintering process. Their presence was characterized by high-resolution transmission electron microscopy. Enhanced reversible domain wall motion was verified by in situ high-energy X-ray diffraction. Electric-field-induced strain is enhanced by 62% and 200% at 25 °C and 150 °C, respectively. Considering lead-free piezoelectrics also represent an emerging class of biomaterials for medical technology, the non-toxicity and biocompatibility of the investigated compositions are examined by in vitro cell viability assays. Our results demonstrate that microstructural engineering is a promising alternative approach to enhance the electric-field-induced strain of lead-free piezoelectrics while maintaining biocompatibility

High-field nonlinear properties and characteristics of domain wall motion in Fe2O3 doped PMnS-PZN-PZT ceramics

High-field nonlinear dielectric and piezoelectric properties of Fe2O3 doped PMnS-PZN-PZT high-power piezoelectric ceramics are investigated. Rayleigh analysis reveals the presence of contributions from lossless reversible domain wall motion and the associated decoupling of nonlinearity and losses. This behavior is attributed to the orderly distribution of defect pinning centers. With the increase in temperature, the high-field nonlinearity becomes more pronounced. It is suggested that the depinning of domain walls arising from the randomization of defect pinning centers is responsible for this enhancement of high-field nonlinearity at the elevated temperatures.

Ba1-xCaxTi0.90Zr0·10O3 shear properties and their frequency dependence determined from ceramic plates by an effective method for resonance decoupling

Thickness poled, monomodal shear plate resonators were used for determination of shear coefficients of piezoelectric Ba1−xCaxTi0.90Zr0·10O3 ceramics with x = 0.10–0.18. The analysis of the impedance at resonance to obtain the coefficients was made by an iterative automatic method. All ceramics have d15 values close to d33 ones, meaning that they have mixed characteristics of extender and rotator ferroelectrics. We are able to effectively produce periodically decoupled fundamental shear modes in the thickness poled plate. We demonstrate this procedure for x = 0.15 ceramics and use it for the frequency dependence study of the properties determined from fundamental shear modes. The material stiffens up, is less piezoelectric and has higher losses as the frequency increases. This is due to the high contribution of the reversible domain wall motion to the piezoelectric activity in BCZT and the lower mobility, and higher internal friction, of the ferroelectric-ferroelastic domains as the frequency increases.

Controlled 90° domain wall motion in BaTiO3 piezoelectric ceramics modified with acceptor ions localized near grain boundaries

The irreversible motion of non-180° ferroelectric domain walls is a predominant cause for the increased hysteretic loss in piezoelectric ceramics at elevated temperatures. In this study we designed piezoelectric ceramics modified with acceptor ions localized near grain boundaries for the purpose of suppressing the irreversible domain wall motion at elevated temperatures without diminishing the contribution from the reversible domain wall motion. Particles of undoped BaTiO3 (BT) were coated with Mn-doped BT by a coprecipitation method and then sintered to form a Mn-modified BT ceramic. Structural and dielectric characterizations indicated that the Mn ions in the resulting ceramic were localized near grain boundaries. The measurement of the unipolar electric-field-induced strain was conducted for the Mn-modified and unmodified (pure) BT ceramics at temperatures up to 120 °C (just below the Currie temperature) to discuss the hysteretic behavior in their piezoelectric response. The results showed that the effective piezoelectric coefficient d 33 * of the Mn-modified BT ceramic was comparable to the unmodified BT ceramic. The hysteresis of the Mn-modified BT ceramic was retained below 40% in the whole temperature range whereas that of the unmodified BT ceramic increased significantly at elevated temperatures over 100 °C. The results in this study demonstrate that the localized Mn ions effectively pin the domain walls to suppress their irreversible motion at elevated temperatures, while the reversible motion inside the grains remains possible.

Current-induced domain wall oscillations in a nanowire imaged by time-resolved photoemission electron microscopy

Abstract We study reversible domain wall motion in half-ring Ni 80 Fe 20 nanowires on a nanosecond (ns) timescale in a truly current-induced pump-probe experiment using an energy filtered, aberration-corrected photoemission electron microscope. The X-ray magnetic circular dichroism signal is probed at different time delays before, during and after the current pulse in a stroboscopic mode with circularly polarized synchrotron radiation in the energy range of the Fe L 3 -edge (707 eV). We observe lateral domain wall oscillations with a frequency of ∼ 0.4 GHz. Comparing the results to a proposed string model, we find that the domain wall oscillations can be described as string-like asymmetric oscillations.

The phase structure and dielectric properties around a new type of phase boundary in a lead ytterbium niobite based solid solution.

The phase boundaries of dielectric materials have constantly been valuable for instructing the design of phase structures, revealing correlations between compositions and structures, and attaining the desired functional properties for piezoelectric, pyroelectric, electrostriction, electrocaloric, energy storage and energy harvesting applications. We here observe a new type of phase boundary in a solid solution of xPbTiO3·(1 - x)Pb(Yb1/2Nb1/2)O3 (x = 0.00-0.20), which is between an antiferroelectric (AFE) phase and a relaxor ferroelectric (RFE) phase. x = 0.10 is confirmed as the phase boundary. XRD, TEM, PFM and Raman spectroscopy analysis reveal two fundamental traits of the phase structure: (1) the polar state changes from AFE to FE order; and (2) the domain range evolves from micrometer-sized to nanometer-sized, both of which are normally separated but coexist around the phase boundary. The intriguing phase structure contributes to the distinctive dielectric properties: (1) a broad compositional zone (x < 0.10 and x ≥ 0.14) features low remnant polarization, low hysteresis and highly reversible domain wall motion, and is expected to be utilized for dielectric energy storage and electrostriction applications; and (2) a narrow nonergodic RFE zone (0.10 ≤ x < 0.14) demonstrates remnant and maximum polarization, co-dominated by composition and temperature, and has potential for pyroelectric and electrocaloric applications.

Rayleigh analysis of domain dynamics across temperature induced polymorphic phase transitions in lead-free piezoceramics (1−x)(BaTi0.88Sn0.12)–x(Ba0.7Ca0.3)TiO3

We carried out a Rayleigh analysis of the dielectric permittivity of a lead-free piezoceramic system (1−x)(BaTi0.88Sn0.12)–x(Ba0.7Ca0.3)TiO3 across the composition and temperature induced polymorphic phase transformations to determine the trend in the reversible and irreversible domain wall motion across the composition and temperature induced structural changes. Experiments were carried out on three representative compositions x = 0.10, 0.2, and 0.25 exhibiting rhombohedral, orthorhombic, and tetragonal phases at room temperature. While confirming that the irreversible Rayleigh parameter is large in the orthorhombic phase, we discuss a correspondence between the reduction in the coercive field and the corresponding increase in the irreversible Rayleigh parameter. We also show how the proximity of the Curie point to the polymorphic phase boundary greatly undermines this correspondence.

Rayleigh Region in Amorphous and Nanocrystaline FINEMET Alloy

Magnetization processes in ferromagnetic materials can be described in four ways, reversible and irreversible domain wall (DW) motion, rotation of the vector of magnetic polarization, and paraprocess in high magnetic elds. The process of reversible DW motion is characteristic for the range of small exciting magnetic elds the Rayleigh region (RR). The dependence of magnetic polarization J in this region, called also the region of initial susceptibility (permeability), on the magnetic eld strength H can be expressed by the following equation

Major contributor to the large piezoelectric response in (1 − x)Ba(Zr0.2Ti0.8)O3 − x(Ba0.7Ca0.3)TiO3 ceramics: Domain wall motion

The piezoelectric activity of lead-free Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT) ceramics has been investigated as a function of composition by using Rayleigh analysis under subswitching-electric-field in combination with large-electric-field strain measurement. The result shows that the intrinsic piezoelectric response exhibits peak values in the vicinity of composition-induced R (rhombohedral)-MPB (morphotropic phase boundary) and MPB-T (tetragonal) phase transitions, but being much less than total d33 value. On the other hand, the extrinsic piezoelectric response, especially the one associated with reversible domain wall motion, has been greatly enhanced in the phase instability regime. Our results indicate that the extrinsic piezoelectric activity is the major contributor to the high piezoelectricity in BZT-xBCT ceramics.

Magnetic Evaluation of Microstructure Changes in 9Cr-1Mo and 2.25Cr-1Mo Steels Using Electromagnetic Sensors

This paper presents results from a multi-frequency electromagnetic sensor used to evaluate the microstructural changes in 9Cr-1Mo and 2.25Cr-1Mo power generation steels after tempering and elevated temperature service exposure. Electromagnetic sensors detect microstructural changes in steels due to changes in the relative permeability and resistivity. It was found that the low frequency inductance value is particularly sensitive to the different relative permeability values of both steels in the different microstructural conditions. The changes in relative permeability have been quantitatively correlated with the microstructural changes due to tempering and long-term thermal exposure, in particular to changes in martensitic/bainitic lath size and number density of carbide precipitates that determine the mean free path to reversible domain wall motion. The role of these microstructural features on pinning of magnetic domain wall motion is discussed.

Polarization reversal and dynamic scaling of (Na0.5K0.5)NbO3 lead-free ferroelectric ceramics with double hysteresis-like loops

The polarization reversal and dynamic hysteresis of ferroelectrics specially with double hysteresis-like loops were investigated by using CuO-doped (Na0.5K0.5)NbO3 ceramics. The variation of the hysteresis area and current density clearly suggests three stages of the polarization reversal. It was found that the hysteresis behavior of the dynamics can be scaled as power law relationships apart from the second stage, where different numbers of domains can be rapidly activated. The main polarization mechanism was ascribed to the reversible domain wall motion (field amplitude Eo &amp;lt; 0.5Ec) and 180° domain switching (0.5Ec &amp;lt; Eo &amp;lt; Ec) for the first stage, and to the non-180° domain switching (Eo &amp;gt; 3.5 kV/mm) for the third stage.

Magnetic configuration of submicron-sized magnetic patterns in domain wall motion memory

We observed magnetic configuration and its change by external magnetic fields in submicron-sized U- and H-shaped NiFe patterns with an x-ray magnetic circular dichroism photoemission electron microscope. The microscope images showed the formation of a single domain wall (DW) with transverse structure at one corner of the U- and H-shaped patterns by applying the magnetic field from the oblique direction. By applying the magnetic field from the direction parallel to a horizontal bar in the patterns, the magnetic configuration in the U-shaped pattern was changed and four patterns were formed: (1) the DW moved from one trap site to another, (2) the DW moved beyond the trap site and formed a single domain, (3) the DW moved and stopped between the trap sites, and (4) the DW remained at the initial position. Only pattern (1) showed reversible DW motion, although pattern (2) was predominantly formed. In contrast, the magnetization configurations showed pattern (1), and reversible DW motion was observed for more than 80% of the H-shaped patterns. Micromagnetic simulation revealed that the DW in the U-shaped pattern was not sufficiently fixed at the corner and easily moved and vanished at the edge of the patterns because the magnetization in the two parallel bars rotated with a magnetic field. The DW was trapped with sufficient strength at the corner, and DW motion occurred only between the trap sites for the H-shaped patterns. The DW motion process was observed with an in situ magnetic field using the x-ray magnetic circular dichroism photoemission electron microscope and the process could be optimized by controlling the pattern shape.

Reversible and irreversible current induced domain wall motion in CoFeB based spin valves stripes

The authors present results on current induced domain wall motion in Co∕Cu∕CoFeB trilayered stripes. The threshold current densities are around 106A∕cm2 at zero field, i.e., about two orders of magnitude smaller than in single NiFe stripes. The domain wall motion is assisted when the field torque acts in the same direction as the spin torque. When the field torque is opposed to the spin transfer one and above a threshold field, the authors observe a reversible displacement of the domain wall (peak in the dV∕dI measurements). This can be ascribed to the onset of domain wall fluctuations, which is confirmed by micromagnetic simulations.

Reversible and irreversible switching processes in pure and lanthanum modified lead zirconate thin films

The mechanism of field induced phase switching in antiferroelectric lead zirconate and La-modified lead zirconate thin films has been analysed in terms of reversible and irreversible switching process under weak fields as a function of donor concentration. Extension of Rayleigh law of ferromagnetic materials to the present antiferroelectric and modified antiferroelectric compositions have clearly showed that origin of small signal dielectric permittivity is due to reversible domain wall motion. Rayleigh's constant, a measure of irreversible switching process, exhibited a slight increase with lower La 3+ concentrations and followed by a gradual fall for higher concentration. This clearly illustrates that donor addition to antiferroelectric thin films controls the domain switching even under weak fields.

Effect of ion-implantation on magnetization processes of 3% SiFe determined by susceptibility spectrum

Rectangular 3% SiFe samples with 0° and 90° cut angles α with respect to the [0 0 1] direction were implanted by N-ion in the fluence range of n=5×10 16–5×10 18 ions/cm 2. The susceptibility spectra originating from both relaxation processes of reversible domain wall motion and magnetization rotation are separated from the complex susceptibility spectrum measured for the samples. The variation of the separated spectra with n showed that the domain wall motion is sensitively affected by the implantation while the magnetization rotation is not affected for both samples with α=0° and 90°. The static susceptibilities χ rev,dw due to reversible domain wall motion is maximum at n=5×10 17 and 5×10 16 ions/cm 2 for α=0° and α=90° samples, respectively, and significantly decreases at n=5×10 18. The relaxation frequency f rev,dw of reversible domain wall motion is nearly constant up to n=5×10 17 ions/cm 2 for both α’s, and then increases for the further increase in n. The change of χ rev,dwand f rev,dwwith n indicates that the decrease in the distance between adjacent pinning sites is the dominant effect on the magnetization by reversible domain wall motion at relatively low ion fluence, while the increase in internal stress is the significant effect at high ion fluence.

Determination of magnetization rotation and domain wall motion components in reversible complex susceptibility spectra of Co-based amorphous ribbons with various annealing times

The complex susceptibility spectra for the Co 66Fe 4Ni 1B 14Si 15 ribbons annealed at 380°C under external magnetic field of 3 Oe with various annealing times were measured in reversible magnetization range. The susceptibility spectra originating from both relaxation processes of reversible domain wall motion and magnetization rotation are separated from the complex susceptibility spectra measured for the samples. The variation of static susceptibilities and relaxation frequencies of domain wall motion and magnetization rotation with annealing time indicate that the alignment of domains to external field direction onset at the annealing time is about 5 min and is accomplished at about 20 min. For short annealing time <5 min, magnetic softening is the main effect on magnetization processes.

Effect of ion implantation on magnetic relaxation of 3% SiFe

The susceptibility spectra originating from both relaxation processes of reversible domain wall motion and magnetization rotation are decomposed from the susceptibility spectrum for 3% SiFe samples implanted by N-ion in the fluence range of n=5×10 −5–5×10 18 ions/cm 2. The static susceptibilities due to domain wall motion and magnetization rotation are maximum at n=5×10 17 ions/cm 2. The relaxation frequencies of domain wall motion and magnetization rotation are not changed significantly up to n=5×10 17 ions/cm 2, and then rapidly increased with the further increase in the ion fluence. The variation of static susceptibilities and relaxation frequencies with n indicate that increase in number of pinning sites for n⩽5×10 17 ions/cm 2 to facilitate magnetization, and then increase in internal stress for n>5×10 17 ions/cm 2 to hinder magnetization.