Ferroelectric Domain Switching Research Articles

Enhanced magnetization in multiferroic nanocomposite Bi0.9Gd0.1Fe0.9Mn0.05X0.05O3 (X= Cr, Co) thin films

In this work, we prepared and investigated the morphology, ferroelectric and magnetic properties of Bi0.9Gd0.1Fe0.9Mn0.05X0.05O3 (X= Cr, Co) nanocomposite thin films. Microstructure study revealed that the surface morphology of the thin films is strongly dependent on the nature of the incorporated transition metal. Room temperature X-ray diffraction and Raman investigations have allowed the identification of formed phases.The local ferroelectric character of these nanocomposites thin films was investigated by piezoresponse force microscopy to get valuable information about the effect of Co3+ and Cr3+ incorporation on ferroelectric domain switching of Bi0.9Gd0.1Fe0.9Mn0.1O3 parent phase. Field dependence of magnetization measurements at room temperature showed that the presence of Co and Cr improved considerably the saturation magnetization with large and narrow open hysteresis loops, respectively. Moreover, the temperature dependence of magnetization measurements revealed the presence of a spin glass behavior in the studied nanocomposites thin films.

Magnetic enhancement of ferroelectric polarization in a particulate multiferroic composite derived in situ via additive assisted sintering of a pseudo ternary alloy system BiFeO3–PbTiO3–DyFeO3

We report here the synthesis of a self-grown 0–3 particulate multiferroic composite by controlled precipitation of the ferrimagnetic garnet phase using additive (MnO2) assisted sintering of a multi-cation ferroelectric system (Bi, Pb, Dy)(Fe, Ti)O3. The particulate multiferroic composite derived in this manner exhibits a favorable microstructure, wherein, although the volume fraction of the garnet phase is kept low (6%), which helps in retaining the electrical insulating character of the specimen, the number fraction of the garnet grains vis-à-vis the ferroelectric grains is ∼1:1. The composite shows a nearly ∼50% increase in saturation polarization at room temperature under a modest magnetic field of 1 T, suggesting a considerable improvement in ferroelectric domain switching due to the efficient strain transfer from the minority garnet grains to the majority piezoelectric grains.

Probing nanoscale structure and strain by dark-field x-ray microscopy

Abstract

A Three-Dimensional Lead Halide Perovskite-Related Ferroelectric

Three-dimensional (3D) organic-inorganic lead halides represented by [CH3NH3]PbI3 perovskite have attracted great interest for their diverse functional properties and promising optoelectronic applications. However, 3D lead halides are still very rare and their ferroelectricity remains controversial. Here, we report an unprecedented 3D lead halide perovskite-related ferroelectric [2-trimethylammonioethylammonium]Pb2Cl6 ([TMAEA]Pb2Cl6), which contains a 3D lead chloride framework of corner- and edge-sharing PbCl6 octahedral, with the [TMAEA]+ cations occupying the voids of the framework. [TMAEA]Pb2Cl6 shows a ferroelectric-to-paraelectric phase transition with the Curie temperature as high as 412 K, a typical ferroelectric hysteresis loop at 293 K with a spontaneous polarization of 1 μC/cm2, and a clear ferroelectric domain switching. To the best of our knowledge, [TMAEA]Pb2Cl6 is the first 3D lead halide showing such an excellent ferroelectricity. Additionally, it also exhibits semiconducting property with a direct bandgap of 3.43 eV. This finding enriches the family of 3D hybrid lead halides, and inspires the exploration of 3D lead halide ferroelectrics.

Rotational intersite displacement of disordered lead atoms in a relaxor ferroelectric during piezoelectric lattice straining and ferroelectric domain switching

We report results of the time-resolved x-ray structure analysis of a relaxor ferroelectric single crystal under an alternating electric field. The time dependence of the lattice strain, atomic displacements, and ferroelectric domain volumes in a $0.955\mathrm{Pb}(\mathrm{Z}{\mathrm{n}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}){\mathrm{O}}_{3}\ensuremath{-}0.045\mathrm{PbTi}{\mathrm{O}}_{3}$ (PZN-4.5PT) single crystal during piezoelectric lattice straining and ferroelectric domain switching is revealed. The lattice strain induced by an electric field is consistent with that expected from the piezoelectric constants. The crystal mosaicity is momentarily increased by a nucleation of nanosized ferroelectric domains when the polarization switching starts. The nucleated ferroelectric domains grow with the time constant of $\ensuremath{\tau}=14\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{s}$. An intersite displacement of the disordered Pb atoms observed in those site occupancies suggests that a rotational intersite displacement of Pb atoms is easily induced by an electric field and causes continuous rotation of the spontaneous polarization. The rotational intersite displacement of Pb atoms is essential for the large piezoelectric lattice strain and fatigue-free ferroelectric domain switching.

90° ferroelectric domain switching effect on interfacial strain mediated magnetoelectric coupling

The phenomena associated with strain-mediated multiferroic behavior have been quantitatively studied by combining synchrotron x-ray diffraction (XRD), ferromagnetic resonance (FMR) and macroscopic strain measurements (digital image correlation) in a magnetoelectric composite (Ni film on PZT substrate). The ferroelectric and piezoelectric strains have been studied by analyzing the evolution of x-ray patterns (peak intensities and shifts), while the magnetic response is studied by FMR (energy shift of the resonance), during in situ application of electrical voltage. Being given the intrinsic selective phase nature of XRD, the lattice strains have also been measured in the Ni film and have been found to be comparable to the macroscopic one (full transmission from the PZT substrate). The PZT strain has been successfully separated into two contributions, i.e. ferroelectric and lattice strains, the first one being five times higher than the second one. Moreover the last is itself composed of two sub-contributions: pure piezoelectric effect and ferroelectric strain in surrounding grains (strain transfer at grain boundaries). Finally, through in situ FMR measurements, we showed that the ferroelectric contribution to the strain-mediated magnetoelectric response is ten times higher than the pure piezoelectric one.

Multi-step domain switching and polarization fatigue in [110]-oriented 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 single crystals

Domain switching in ferroelectrics is at the heart of many functionalities, and the visualization of switching pathway is the key to understand the fundamental properties and to promote the applications of high-performance ferroelectrics. Here, we directly documented the multi-step domain switching in [110]-oriented 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 (PMN-0.33PT) single crystals under a cycling electric field with the help of in situ polarized light microscopy. Based on the characteristic domain configuration analysis, we demonstrated that the 180° switching process was consisted of multi-step 60° switching. Such a multi-step 60° switching pathway resulted in a large negative strain and an internal electric field, which contributes to a large polarization fatigue rate under the alternating electric field. Our works may provide a window to study the domain switching process and its effect on polarization fatigue in relaxor-ferroelectric single crystals.

Voltage-driven annihilation and creation of magnetic vortices in Ni discs.

Using photoemission electron microscopy (PEEM) to image ferromagnetism in polycrystalline Ni disks, and ferroelectricity in their single-crystal BaTiO3 substrates, we find that voltage-driven 90° ferroelectric domain switching serves to reversibly annihilate each magnetic vortex via uniaxial compressive strain, and that the orientation of the resulting bi-domain reveals the chirality of the annihilated vortex. Micromagnetic simulations reveal that only 60% of this strain is required for annihilation. Voltage control of magnetic vortices is novel, and should be energetically favourable with respect to the use of a magnetic field or an electrical current. In future, stray field from bi-domains could be exploited to read vortex chirality. Given that core polarity can already be read via stray field, our work represents a step towards four-state low-power memory applications.

Evolution of the Electrical Displacement and Energy Dissipation of Lead Zirconate‐Titanate Ceramics under Cyclical Load

In this paper, the electromechanical behavior of lead zirconate‐titanate ceramics (P51) has been characterized and modeled. The variation of the energy dissipation and peak electrical displacement of the P51 ceramic has been investigated in details. The total strain of P51 under cyclical loading consists of elastic deformation (), immediate ferroelectric domain switching deformation (), and time‐dependent deformation (). Thus, an expression for the energy dissipation of P51 can be theoretically derived. In addition, a practical method for calculating the dissipated energy has been proposed by integrating the curve of a hysteresis loop. The experimental results show that the peak electrical displacement and dissipated energy both decrease monotonously with the increase of the number of cycles. Furthermore, ferroelectric 90° domain switching was observed by X‐ray diffraction (XRD) and the percentage of domain switching has been calculated by the variation of the peak intensity ratio of (002) to (200) at about 45 degrees. Then, grain debonding, crack, and crush were found around voids inside the specimen by using scanning electron microscope (SEM). It is indicated that switching of more capable‐switch domains stimulates larger dissipated energy and a bigger peak electrical displacement at the initial cyclic loading. Finally, an exponential functional model has been proposed to simulate the peak evolution of electrical displacement based on the energy dissipation of P51 ceramics under cyclical load.

Reproducible Ultrathin Ferroelectric Domain Switching for High-Performance Neuromorphic Computing.

Neuromorphic computing consisting of artificial synapses and neural network algorithms provides a promising approach for overcoming the inherent limitations of current computing architecture. Developments in electronic devices that can accurately mimic the synaptic plasticity of biological synapses, have promoted the research boom of neuromorphic computing. It is reported that robust ferroelectric tunnel junctions can be employed to design high-performance electronic synapses. These devices show an excellent memristor function with many reproducible states (≈200) through gradual ferroelectric domain switching. Both short- and long-term plasticity can be emulated by finely tuning the applied pulse parameters in the electronic synapse. The analog conductance switching exhibits high linearity and symmetry with small switching variations. A simulated artificial neural network with supervised learning built from these synaptic devices exhibited high classification accuracy (96.4%) for the Mixed National Institute of Standards and Technology (MNIST) handwritten recognition data set.

Dielectric and ferroelectric properties of BTFCO thin films

Single phase Bi3.25La0.75Ti2.5Nb0.25Fe0.125Co0.125O12 (BTFCO) thin films were deposited on Pt/TiO2/SiO2/Si substrates by RF-magnetron sputtering. Ferroelectric domain switching, including 180° and non-180° domains walls, was observed in polarization- electrical field hysteresis loops. The coercive field Ec of the materials, linking with zero polarization, is near 100 kV/cm. Dielectric permittivity changing with DC electric field shows one permittivity peak near 50 kV/cm, which suggests that field induced switching of 180° domains is completed at 50 kV/cm. Further increasing the DC field causes the decrease of dielectric permittivity, which can be attributed to the decrease of density of 90° domain walls. The difference between the Ec and the field for permittivity peak show that the switching field of 180° domain is lower than that of 90° domains in BTFCO ferroelectric films.

Application of a graphical method to the domain switching of ferroelectrics subjected to electromechanical loading

A change in the system Gibbs free energy can be used as a criterion for spontaneous reactions, including the ferroelectric domain switching process. In this work, a new effective graphical method is introduced to investigate the change in the Gibbs free energy of a grain system and intuitively represent the domain switching state since its expression is too complex to study directly. A barium titanate crystal is considered as an example, and only 90∘ domain switching is involved. We can obtain two kinds of applications by virtue of the graphical method by controlling different variables in the change of the free energy: one application involves a new form of a ferroelectric domain switching criterion that considers the effect of the grain size, and the other application involves the critical single-domain grain size. For different loading methods, there will be different critical single-domain grain sizes in ferroelectrics.

Nanoscale Probing of Ferroelectric Domain Switching Using Piezoresponse Force Microscopy

In ferroelectric materials, piezoresponse force microscopy (PFM) has been widely used to explore ferroelectric domain switching. In this article, we review the fundamentals of nanoscale probing of ferroelectric domain switching using PFM, including the basic principles of PFM and a variety of PFM studies on local domain switching. We also introduce advanced PFM techniques for exploring switching behavior. Finally, we discuss several issues and perspectives in nanoscale probing of ferroelectric domain switching using PFM. PFM has played an important role in exploring switching behavior in ferroelectric materials, and it could be further developed to probe more detailed switching information. Key words: Ferroelectric domain, Piezoresponse force microscopy, Switching behavior, Capacitor

Relaxor ferroelectric and photocatalytic properties of BaBi4Ti4O15

ABSTRACTAurivillius phase BaBi4Ti4O15 micro-sized powders were produced by solid-state reaction and their photocatalytic properties were reported for the first time. X-ray diffraction revealed the polar orthorhombic structure. BaBi4Ti4O15 ceramics exhibited diffuse phase transition at ∼ 410°C. The freezing temperature of 274°C was obtained by fitting the Vogel–Fulcher law. The distinct ferroelectric domain switching current peaks in current – electric field (I-E) loop and piezoelectric coefficient d33 value of 7.0 ± 0.1 pC/N at room temperature further demonstrated relaxor ferroelectric behaviour of BaBi4Ti4O15. UV-vis absorption spectra indicated that BaBi4Ti4O15 had a direct band gap of 3.2 eV. The photocatalytic study showed 15% degradation of Rhodamine B (RhB) solution by BaBi4Ti4O15 powders after 3.5 h UV-vis irradiation. The RhB degradation rate was further enhanced by depositing Ag nanoparticles on the BaBi4Ti4O15 powders surface. This work suggested that the relaxor ferroelectric BaBi4Ti4O15 is promising for photocatalytic applications.

Atomic structure of domain and defect in layered-perovskite Bi2WO6 thin films

Layered-perovskite oxide thin films provide new opportunities to design next-generation electronic devices with their special structure and potentially excellent electrical properties. The microstructure and domain structure in epitaxial Bi2WO6 (BWO) thin films have been investigated by advanced transmission electron microscopy (TEM) combined with piezoresponse force microscopy (PFM). A slight distortion of oxygen octahedron, which accompanies the movement of the Bi2O2 fluorite-like sheet relative to the perovskite-like WO4 blocks, results in the formation of 90° domains. A kind of nanoscale defect is characterized by aberration-corrected scanning transmission electron microscopy (AC-STEM). An extra Bi-O layer is suggested to be presented at the Bi2O2 fluorite-like sheet. The present study may help to enrich the understanding of ferroelectric domain switching on the microscopic scale and the effect of defects on the ferroelectric property.

Shear-strain-mediated magnetoelectric effects revealed by imaging.

Large changes in the magnetization of ferromagnetic films can be electrically driven by non-180° ferroelectric domain switching in underlying substrates, but the shear components of the strains that mediate these magnetoelectric effects have not been considered so far. Here we reveal the presence of these shear strains in a polycrystalline film of Ni on a 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 substrate in the pseudo-cubic (011)pc orientation. Although vibrating sample magnetometry records giant magnetoelectric effects that are consistent with the hitherto expected 90° rotations of a global magnetic easy axis, high-resolution vector maps of magnetization (constructed from photoemission electron microscopy data, with contrast from X-ray magnetic circular dichroism) reveal that the local magnetization typically rotates through smaller angles of 62-84°. This shortfall with respect to 90° is a consequence of the shear strain associated with ferroelectric domain switching. The non-orthogonality represents both a challenge and an opportunity for the development and miniaturization of magnetoelectric devices.

Direct observation of magnetism controlled by electric fields for CoFeB mesoscopic islands on PMN-PT

Electric field control of magnetism at the microscopic scale is vital for high-density magnetic storage, and has developed rapidly in recent years. Here, we report three types of magnetic responses under in situ electric fields for different mesoscopic CoFeB islands on one PMN-PT single crystal, including Type I, which shows no changes of the magnetic hysteresis under different electric fields, Type II, which shows obvious changes and remains after the electric fields are removed, and Type III, which displays a combined behavior of Type I and Type II. In addition, Type II displays four subtypes according to the relation between coercivity and remanence ratio. These phenomena can be attributed to 109° or 180°/71° ferroelectric domain switching, as well as the complex magnetization reversal mechanism.

Electric field tuning non-volatile dynamic magnetism in half-metallic alloys Co2FeAl/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure

The half-metallic characteristic of Co2FeAl Huesler alloy films in Co2FeAl/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure was controlled by different substrate temperatures during deposition. The evolution of microstructure shows the B2 ordering degree of Co2FeAl thin film increase with the substrate temperature decreasing from 550 °C to 480 °C during deposition, which can be verified by anisotropy magnetoresistance measurement. Moreover, the result measured by rotating-angle ferromagnetic resonance demonstrates B2 ordering degree of Co2FeAl thin film controlled the change of symmetry of magnetic anisotropy. In addition, the loop-like curve of magnetic resonance field/linewidth versus electric field exhibits the non-volatile behavior, which can be attributed to the 109° ferroelectric domain switching of PMN-PT substrate. This result can provide opportunities for magnetization control in multiferroic devices.

Revisiting KAI theory and its application to mixed composite system “–PVA” fabricated at moderate elevated temperature

Ishibashi and Takagi considered ‘ferroelectric domain switching’ just equivalent to ‘phase evolution during crystal growth’. They slightly modified Kolmogorov and Avrami’s classical theory of ‘phase transformations in crystal growth’ and applied it to the switching data in ferroelectrics. Here an effort is made to elucidate mathematical steps in evolution of this new KAI model used to fit experimental switching data to estimate microscopic switching parameters. In mixed composite system (x = 0.09), the domain growth dimension () is found to expand from to when signal amplitude changed from to The cesium substitution is supposed to have enabled lone pairs on central nitrogen of nitrite group to orient constituting branches into more ordered state in the matrix of molecular chains of the PVA facilitating control of crystallization process which led to lowering of strain giving rise to the increased change in with change in pulse amplitude.

Phase-field modeling of the coupled domain structure and dielectric breakdown evolution in a ferroelectric single crystal.

The study of domain switching and dielectric breakdown behavior of ferroelectrics together with their relations is crucial for understanding the essence of ferroelectric physics and exploring their applications. In this work, a phase-field method is developed to reveal the coupled domain structure and dielectric breakdown evolution in a ferroelectric single crystal (FSC) by employing the Ginzburg-Landau kinetic equation and Griffith type energy criterion. Results show that the domain switching mobility, symbolizing the speed of polarization evolution, has a significant influence on ferroelectric properties, namely coercive field, dielectric breakdown strength (DBS), discharge energy density (DED), and energy storage efficiency (ESE). It is found that FSC with the higher domain switching mobility always displays a lower coercive field and smaller remanent electric displacement (or polarization) together with a higher DBS, accounting for a higher DED and ESE. Such findings can provide effective guidance in understanding and designing high-DBS and high-energy-density ferroelectrics. In addition, the defect concentration has a significant influence on the DBS and the pattern of breakdown paths.