Domain Switching Research Articles

Berry curvature induced spontaneous and topological-like Hall effect in magnetic Weyl semimetallic Nd2Ir2O7 (111) thin films

We report a study of longitudinal resistivity, anisotropic magnetoresistance (MR), and Hall effect on epitaxial Nd2Ir2O7 (111) thin films grown by the solid phase epitaxy technique, in which spin–orbit coupling, electronic correlation, magnetic frustration, and f-d exchange interaction are present. Temperature-dependent longitudinal resistivity (ρxx) data indicate semimetallic charge transport in the low-temperature region. Field-cooled longitudinal resistivity measurements detect negligible domain-wall conductance compared to the polycrystal or single-crystal samples. Angle-dependent MR measurement shows that the magnetic structure of Ir4+ 5d moments can be finely tuned by applying a magnetic field along different crystallographic directions. MR measurements show a field-induced modification of the Nd3+ 4f spin structure from all-in-all-out/all-out-all-in (AIAO/AOAI) (4-in-0-out) to 1-in-3-out for the applied field (H) along the [111] direction, resulting in field-induced plastic deformation of the Ir4+ domain distribution. In contrast, the application of field (H) along the [001] and [011] directions could not modify any domain distribution. A large spontaneous Hall effect (SHE) signal has been observed on Nd2Ir2O7 (111) thin film with AIAO/AOAI antiferromagnetic ordering for the application of field (H) along [001], [1̄1̄0], and [111] directions. The appearance of a large spontaneous Hall signal for the applied field along [001] and [1̄1̄0] directions rules out domain switching as the origin of the Hall effect and confirms the presence of the Weyl semimetallic phase in Nd2Ir2O7 (111) thin films. In addition to SHE, a large topological-like Hall signal is also observed, possibly due to the presence of multiple Weyl nodes in the electronic band structure.

Fabrication of highly oriented Mn4N/Pt epitaxial bilayer structure on MgO(001) for spintronics applications

Magnetization control by electric current or spin current is an attractive technology with potential applications in memory and logic devices, and Mn4N has attracted much attention in recent years as a candidate material for current-induced magnetization switching and magnetic domain wall motion, as well as a skyrmion material. For these applications, a bilayer structure of Mn4N and heavy metals must be formed with high crystalline quality. In this study, we have achieved the epitaxial growth of Mn4N thin films on MgO(001) with a Pt underlayer. The reflection high-energy electron diffraction images and x-ray diffraction ω-rocking curves show that the Mn4N films fabricated on the Pt underlayers exhibit higher crystalline quality than the Mn4N films directly formed on the MgO. Furthermore, anomalous Hall effect loops with bump-like structures were observed. This is considered to be due to the topological spin texture. The Mn4N/Pt epitaxial bilayer structure has potential for use in spin–orbit torque applications and is a candidate configuration for topological spin textures.

Domain reorientation and electric-field-induced phase transition in (K,Na)(Nb,Sb)O3-(Bi,Na)ZrO3 piezoceramics

Polymorphic phase transition boundary (PPB) strategy is effective in designing high-performance piezoelectric materials in (K0.5Na0.5)NbO3 (KNN)-based systems. However, the underlying mechanism of large piezoelectric response in KNN-based is still blurry and thus needs to be explored properly. In this paper, it is found that the domain reorientation becomes easier and more sufficient in the KNN-based ceramics with two-phase coexistence. Moreover, in situ transmission electron microscope experiments disclose the occurrence of a new intermediate phase under an external electric filed, which could relieve the internal stress generated by the domain reorientation and then facilitate the further domain switching along the electric field direction. The enhanced domain reorientation contributes to the high piezoelectric response in PPB region (d33 = 438 pC/N, kp = 48%, d33* = 520 p.m./V at 1.5 kV/mm). Our work provides an in-depth understanding of the contribution of the domain switching and electric-filed-induced phase transition to piezoelectric properties in KNN-based ceramics, which shall benefit the design of new lead-free high-performance piezoelectric materials.

Preparation of cement modified by multi-walled carbon nanotubes and investigation of its piezoelectric property

This study focuses on investigating the properties of a cement-based piezoelectric composite modified with 0.5 % Multi-Walled Carbon Nanotubes (MWCNTs) under varying stress conditions. Through calibration methods, a critical point named G was identified at around 60.4 MPa. Below this point, the force-electric response displayed a linear relationship, characterized by an average sensitivity of 117 pC/N. Conversely, above this point, non-linear behavior surfaced due to internal damage within the piezoelectric ceramic, leading to diminished piezoelectric properties. The frequency response characteristics highlighted efficient conversion of pressure signals to electrical signals with minimal delay, showcasing stability across diverse cyclic loading amplitudes. In addition, a dynamic compression experiment revealed sensitivity to strain rate and the notable contribution of domain switching to total strain. Moreover, an analysis of the stress–strain curve under impact load provided insights into the composite's non-linear growth and its response to strain rate variations.

Enhanced piezoelectric properties and depolarization temperature in textured (Bi0.5Na0.5)TiO3-based ceramics via homoepitaxial templated grain growth

Enhanced piezoelectric response was usually achieved in (Bi0.5Na0.5)TiO3 (BNT)-based ceramics with sacrifice of depolarization temperature Td, seriously limiting their usage range in electromechanical applications. In this work, we propose to explore piezoelectric anisotropy and domain engineering in composition & microstructure-controlled textured ceramics to resolve this issue. [001]c-textured 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3 (0.94BNT-0.06BT) ceramics with Lotgering factor F001∼91% were fabricated through homoepitaxial templated grain growth (TGG) via using 0.94BNT-0.06BT microplatelet templates. The textured samples exhibited more ordered domains with facilitated domain switching behavior, being consistent with saturated high polarization achieved at lower electric fields. Increasing F001 to above 60% enables rapid enhancement of piezoelectric response. Notably, compared to non-textured counterpart, the maximally textured ceramics exhibited ∼236% enhanced piezoelectric coefficient (d33∼302 pC/N) and ∼280% enhanced piezoelectric voltage coefficient (g33∼49.8 × 10−3 Vm/N), together with slightly increased depolarization temperature (Td∼106 °C). Moreover, those values are approaching or even higher than the single-crystal values. This work not only provides important guidelines for design and synthesis of novel textured ceramics with improved comprehensive electrical properties, but also can expand application fields of BNT-based ceramics.

Giant strain performance of lead-free relaxor piezoceramics through synergistic compositional and defect engineering

For applications involving high-precision displacement actuators, piezoceramics exhibiting extensive strain and minimal hysteresis are much sought-after. However, achieving extensive strain concurrent with low hysteresis remains a formidable challenge. We hereby propose an innovative design approach, synergistically harnessing compositional and defect engineering, to concurrently boost the strain response and mitigate hysteresis in (Na0.5Bi0.5)TiO3 (NBT)-based ceramics. The defect dipoles are elaborately designed and introduced into the mixed rhombohedral (R) and tetragonal (T) phases system, which causing reversible domain switching, heightening recoverability of electric-field-induced phase transition and augmenting the electrostrictive effect. The synergy of defect dipoles leading to reversible domain switching and electric field-induced phase transitions is further validated via phase-field simulations. Ultimately, a giant strain of 0.62% with low hysteresis of 10.9% and correspondingly high d33* of 1033 pm V−1 were concurrently realized in the designed NBST(1-x)Mnx (x = 0.3%) specimen. This study opens up a feasible and effective way to design piezoelectric materials with both a giant strain and a narrow hysteresis in lead-free actuator materials.

Reversible evolution of ferroelectric-antiferroelectric phase transition in lanthanum-modified NaNbO3-based ceramics

Sodium niobate (NN) lead-free perovskites have been concentrated on due to high performance and abundant phase structure. The complex structure evolution has become a hot topic of research for this kind of materials. In this work, antiferroelectric phase is recovered by introducing La3+ dopant from modified ferroelectric states, indicating reversible composition-induced antiferroelectric-ferroelectric (AFE-FE) phase transition in NN-based ceramics. Significantly, change tendency of decreasing first and then increasing appears for phase transition temperature with increasing La3+, which is different from general phenomenon for ions dopant. Antiferroelectric orthorhombic (Pbma) is induced from ferroelectric tetragonal (P4mm) with a transient state of paraelectric cubic (Pm3m) via enhancing La3+. Further, substitution on A-site and A/B-sites are revealed with low and high content of La3+, respectively, accompanied by decreased first and then increased oxygen vacancy. Moreover, obviously deteriorated piezoelectric response is observed along with poor domain switching due to the vanishing ferroelectric domain for FE-PE-AFE phase transition. Meanwhile, weak strain, piezoelectric and dielectric properties are observed for antiferroelectric phase with antiparallel dipoles, while enhanced strain and dielectric permittivity are gained around ferroelectric-paraelectric coexistence or paraelectric region originating from electric field-induced ferroelectric state from polar nanoregions. Thus, this work demonstrated an abnormal phase transition in NN-based ceramics, promoting the understanding of antiferroelectrics.

Achieving significantly enhanced piezoelectricity in aurivillius ceramics by improving initial polarization and dielectric breakdown strength

In this work, the neglected role of the dielectric breakdown strength (BDS) in piezoelectricity of bismuth layer-structured ferroelectrics (BLSFs) is revealed, enhanced initial polarization and BDS work together to improve the piezoelectricity of CaBi4Ti4O15 (CBT) ceramics via Li/Bi co-substitution. The experimental work, first-principles calculations and finite element simulation are carried out to investigate the effect of Li/Bi co-substitution in depth. The stronger spontaneous polarization (Ps) from the lattice distortion and the more favorable domain switching from the improved grain growth both contribute to an enhanced initial polarization. Besides, the changed grain-scale microstructure improves the hardness and inhibits the local discharge, the higher resistivity related to strong defect dipoles suppresses the heat generation during the poling process, all resulting in an increase of BDS by about 100%, and allowing more domains to align. This work demonstrates an effective strategy to develop BLSFs with enhanced piezoelectricity for high temperature piezoelectric applications.

Evolution Characteristics of Electric Field-Related Properties in Polymorphic Piezoceramics with Temperature-Impelled Phase Transition

In this work, to systematically investigate the evolution characteristics of electrical properties in polymorphic piezoceramics, the Ba(Ti0.92Zr0.08)O3 ceramics are selected as a paradigm that possesses all the general phase structures above room temperature. It is found that the evolution of electrical properties with temperature change can be divided into three stages based on phase structure transforming: high ferroelectric and stable strain properties at R and R-O, high ferroelectric and enhanced strain/converse piezoelectric properties at O, O-T, and T phase, and the rapidly decreased ferroelectric and strain properties in T-C and C phase. However, the ferroelectric and strain properties all increase with rising electric field and their evolution can be divided into two parts based on phase structures. The high property and slow increase rate are present at R, R-O, O, and O-T, while the poor property but a high increase rate is present around T-C. Similar results can be found in the evolution of electrostrictive property. Finally, the highest d33* of ~1240 pm/V and Q33 of ~0.053 m4/C2 are obtained at O-T due to the high ferroelectricity but easy domain switching. This work affords important guidance for the property optimization of polymorphic piezoceramics.

The Effect of Chemical Environment and Temperature on the Domain Structure of Free-Standing BaTiO3 via In Situ STEM.

Ferroelectrics, due to their polar nature and reversible switching, can be used to dynamically control surface chemistry for catalysis, chemical switching, and other applications such as water splitting. However, this is a complex phenomenon where ferroelectric domain orientation and switching are intimately linked to surface charges. In this work, the temperature-induced domain behavior of ferroelectric-ferroelastic domains in free-standing BaTiO3 films under different gas environments, including vacuum and oxygen-rich, is studied by in situ scanning transmission electron microscopy (STEM). An automated pathway to statistically disentangle and detect domain structure transformations using deep autoencoders, providing a pathway towards real-time analysis is also established. These results show a clear difference in the temperature at which phase transition occurs and the domain behavior between various environments, with a peculiar domain reconfiguration at low temperatures, from a-c to a-a at ≈60°C. The vacuum environment exhibits a rich domain structure, while under the oxidizing environment, the domain structure is largely suppressed. The direct visualization provided by in situ gas and heating STEM allows to investigate the influence of external variables such as gas, pressure, and temperature, on oxide surfaces in a dynamic manner, providing invaluable insights into the intricate surface-screening mechanisms in ferroelectrics.

Giant room-temperature modulation of magnetic anisotropy by electric fields in CoFeB/(011)-PMN-PT multiferroic heterostructures with two distinct initial magnetic anisotropies

This paper reports that the in situ growth magnetic field (Hg) during magnetic-phase CoFeB deposition impacts the electric-field control of magnetic anisotropy in Co40Fe40B20/(011)-Pb(Mg1/3Nb2/3)0.7Ti0.3O3 [CoFeB/(011)-PMN-PT] composite multiferroic heterostructures at room temperature. In the Hg1 mode (in situ Hg along the [011¯] direction of the ferroelectric PMN-PT substrate), the electric-field-controlled modulation ratios of the magnetic coercivity HC and saturation magnetic field HS are approximately −47% and +156%, respectively. However, in the Hg2 mode (in situ Hg along the [100] direction of the ferroelectric PMN-PT substrate) of the CoFeB/(011)-PMN-PT multiferroic heterostructure, the electric-field-controlled modulation ratios of the magnetic coercivity HC and saturation magnetic field HS can reach as high as +162% and +393%, respectively. Moreover, the electric-field-controlled magnetic coercive field HC exhibits a butterfly shape when plotted versus the applied electric fields in both modes, which matches the in-plane butterfly strain loop of the ferroelectric PMN-PT substrate. However, the electric-field-controlled saturation magnetic field HS presents a square loop, which is very consistent with the ferroelectric loop of the PMN-PT substrate. This result may be ascribed to the distinct pathway of the ferroelastic domain switching in the (011)-oriented PMN-PT substrate. This study provides a new idea for the design of spintronic devices based on multiferroic heterostructures.

In situ X-ray diffraction analysis of intrinsic and extrinsic piezoelectric response in (100)/(001)-oriented tetragonal multidomain Pb(Zr, Ti)O3 films epitaxially grown on Si substrates

(100)/(001)-oriented tetragonal Pb(Zr,Ti)O3 films with different thicknesses of 400 nm, 1000 nm, 1700 nm, and 2000 nm were epitaxially grown on (100) c SrRuO3//(100)Pt//(100)ZrO2//Si(100) substrates by pulsed laser deposition. Their ferroelectric and piezoelectric properties were investigated by polarization–electric field and strain–electric field measurements with increasing maximum strength of an applied electric field in a triangular wave. The macroscopic piezoelectric response was quantitatively analyzed with respect to the intrinsic and extrinsic contributions based on in situ X-ray diffraction results under an electric field. The domain switching from the (100)- to the (001)-oriented domain and the out-of-plane lattice compression in the (100)-oriented domain were clearly observed under an electric field, while the out-of-plane lattice deformation of the (001)-oriented domain was negligibly small. Furthermore, the effective piezoelectric response due to domain switching increased with the increasing the film thickness, which is attributed to the decrease in the constraint with the increasing film thickness imposed by the substrate.

Design and development of a new lead-free BiFeO3-BaTiO3 quenched ceramics for high piezoelectric strain performance

Designing a new high-performance lead-free ceramic has become a cutting-edge research topic due to growing concerns about the toxic nature of lead-based materials. In this work, a convenient strategy of compositional design and domain engineering is applied to the lead-fee BiFeO3-BaTiO3 ceramics which provides a flexible polarization free-energy profile for domain switching. Here, simultaneously enhanced dynamic piezoelectric constant (d33* ≈ 772 pm/V) and a good thermal-stability (Δd33* ≈ 26% over the temperature of 20–180 °C) are achieved with a high Curie temperature (TC) of 432 °C. This high piezoelectric strain performance is collectively attributed to multiple effects such as thermal quenching, suppression of defect charges by donor doping, chemically induced local structure heterogeneity, and electric field-induced phase transition. Furthermore, the addition of BT content decreased octahedral tilting that reduce anisotropy for domain switching and increased in tetragonality (cT/aT) providing a wider polar length for B-site cation displacement, leading to high piezoelectric strain performance. Atomic-resolution transmission electron microscopy and piezoelectric force microscopy combined with X-ray diffraction results strongly support the origin of high piezoelectricity. The high and temperature-stable piezoelectric strain response of this work is superior to those of other lead-free ceramics. The synergistic approach of composition design and the concept present here for the origin of high strain response provides a paradigm for the development of new materials for high-temperature piezoelectric actuator applications.

Bubble domain evolution in well-ordered BiFeO3 nanocapacitors

Ferroelectric nanocapacitors have attracted intensive research interest due to their novel functionalities and potential application in nanodevices. However, due to the lack of knowledge of domain evolution in isolated nanocapacitors, precise manipulation of topological domain switching in the nanocapacitor is still a challenge. Here, we report unique bubble and cylindrical domains in the well-ordered BiFeO3 nanocapacitor array. The transformation of bubble, cylindrical and mono domains in isolated ferroelectric nanocapacitor has been demonstrated via scanning probe microscopy (SPM). The bubble domain can be erased to mono domain or written to cylindrical domain and mono domain by positive and negative voltage, respectively. Additionally, the domain evolution rules, which are mainly affected by the depolarization field, have been observed in the nanocapacitors with different domain structures. This work will be helpful in understanding the domain evolution in ferroelectric nanocapacitors and providing guidance on the manipulation of nanoscale topological domains.

Induction and Ferroelectric Switching of Flux Closure Domains in Strained PbTiO3 with Neural Network Quantum Molecular Dynamics.

We have developed an extension of the Neural Network Quantum Molecular Dynamics (NNQMD) simulation method to incorporate electric-field dynamics based on Born effective charge (BEC), called NNQMD-BEC. We first validate NNQMD-BEC for the switching mechanisms of archetypal ferroelectric PbTiO3 bulk crystal and 180° domain walls (DWs). NNQMD-BEC simulations correctly describe the nucleation-and-growth mechanism during DW switching. In triaxially strained PbTiO3 with strain conditions commonly seen in many superlattice configurations, we find that flux-closure texture can be induced with application of an electric field perpendicular to the original polarization direction. Upon field reversal, the flux-closure texture switches via a pair of transient vortices as the intermediate state, indicating an energy-efficient switching pathway. Our NNQMD-BEC method provides a theoretical guidance to study electro-mechano effects with existing machine learning force fields using a simple BEC extension, which will be relevant for engineering applications such as field-controlled switching in mechanically strained ferroelectric devices.

In-situ measurement of thermal depolarization in tetragonal BS-PT piezoelectric ceramics

High temperature depolarization poses a significant challenge to the practical application of piezoelectric/ferroelectric materials. Determining the depolarization temperature (Td) in such materials is crucial for evaluating their performance under high temperature conditions. Here, we propose a method for observing thermal depolarization by examining the 90º domain switching induced strain. Our results show that the differential thermal expansivities of unpoled and poled tetragonal BiScO3-PbTiO3 (BS-PT) piezoelectric ceramic samples can distinguish between thermal expansion strain and 90º domain switching induced strain. The effectiveness of our proposed method is further confirmed by quantitatively analyzing the 90º domain via X-ray diffraction. Compared to the in-situ resonance-antiresonance impedance spectrum, our method allows for more accurate testing of depolarization temperature, demonstrating significant potential for the direct observation of thermal depolarization in piezoelectric/ferroelectric materials.

Mechanism of polarization “Wake-Up” in ferroelectric Hafnia-Zirconia thin films

As an emerging non-volatile memory technology, HfO2-based ferroelectrics exhibit excellent compatibility with silicon CMOS process flows; however, during repeated programming and erase of the polarization state of HfO2-based ferroelectric capacitors, the magnitude of the measured polarization increases, a phenomenon known as “wake-up”. Here-in, we study the cause of wake-up effect in Hf0.5Zr0.5O2 (HZO) capacitors using non-destructive methods that probe statistically significant sample volumes. Synchrotron X-ray diffraction reveals a concerted shift in HZO Bragg peak position as a function of polarization switching cycle number in films prepared under conditions such that they exhibit extremely large (∼3000%) wake-up. Piezoresponse force microscopy measurements are utilized to visualize domain switching with wake-up. The combination of these observations clearly demonstrates that wake-up is caused by a field driven phase transformation of the tetragonal phase to the metastable ferroelectric orthorhombic phase during polarization switching of HZO capacitors.

Reliability characterization of non-hysteretic charge amplification in MFIM device

A measurement procedure is presented to characterize the degradation of the hysteresis free charge amplification in unipolar operation of negative capacitance capacitors. Two different degradation processes are identified from these measurements and are related to remanent switching of domains and a change in the electrical internal bias field.

Pinning and Depinning of Domain Switching in Ferroelectric HfO2 Freestanding Membrane.

Pinning and Depinning of Domain Switching in Ferroelectric HfO2 Freestanding Membrane.

Ultralow Tip-Force Driven Sizable-Area Domain Manipulation through Transverse Flexoelectricity.

Deterministic control of ferroelectric domain is critical in the ferroelectric functional electronics. Ferroelectric polarization can be manipulated mechanically with a nano-tip through flexoelectricity. However, it usually occurs in a very localized area in ultrathin films, with possible permanent surface damage caused by a large tip-force. Here it is demonstrated that the deliberate engineering of transverse flexoelectricity offers a powerful tool for improving the mechanical domain switching. Sizable-area domain switching under an ultralow tip-force can be realized in suspended van der Waals ferroelectrics with the surface intact, due to the enhanced transverse flexoelectric field. The film thickness range for domain switching in suspended ferroelectrics is significantly improved by an order of magnitude to hundreds of nanometers, being far beyond the limited range of the substrate-supported ones. The experimental results and phase-field simulations further reveal the crucial role of the transverse flexoelectricity in the domain manipulation. This large-scale mechanical manipulation of ferroelectric domain provides opportunities for the flexoelectricity-based domain controls in emerging low-dimensional ferroelectrics and related devices.