Ferroelectric domain walls have emerged as promising building blocks for next-generation nanoelectronics. Recent studies have revealed that large-angle c/a twin boundaries in lead-based ferroelectric thin films exhibit superior physical properties, including enhanced piezoelectric responses, flexoelectric effects, and multi-caloric behaviors. However, the realization of analogous c/a ferroelastic structures in lead-free BiFeO3 (BFO) thin films remains challenging. Here, we report the successful construction of coherent pseudo-c/a twin domain walls in highly tetragonal Ga-doped BFO thin films. These domain boundaries are found to accommodate cross-hatched polarization arrays that effectively compensate domain wall electrostatics, along with a markedly enhanced flexoelectric effect. Moreover, these twin boundaries exhibit polarization-gated switchable conductivity, highlighting their potential for use in memory devices. Our work offers new insights into the design of large-angle ferroelectric domain walls and lays a foundation for future domain-wall-based electronic applications.

Multiferroic oxides, such as BiFeO3, have garnered significant attention due to their coupled ferroelectric, magnetic, and elastic properties, offering exciting opportunities for multifunctional device applications. Controlling phase transitions in these materials is critical for tuning their physical properties and achieving desired functionalities. While numerous studies have focused on ferroelectric-ferroelectric transitions at rhombohedral-tetragonal morphotropic phase boundaries, far less attention has been given to the ferroelectric-antiferroelectric phase boundaries. Such systems hold promise for discovering novel physical phenomena, such as reversible phase transitions, enhanced piezoelectricity, and magnetoelectric coupling. In this work, we report a reversible antiferroelectric-to-ferroelectric phase transition in La doped BiFeO3 thin films. By modulating the residual strain via film thickness, an antiferroelectric orthorhombic phase is stabilized within a ferroelectric rhombohedral phase matrix. Under an external electric field, the phase transitions reversibly between these two states. This discovery not only enriches the understanding of orthorhombic-rhombohedral morphotropic phase boundaries but also provides a potential pathway for developing magnetoelectric devices with enhanced functionality.

Ferroelectric topologies, renowned for their nanoscale dimensions and external electric field tunability, are emerging as leading candidates for high-density, low-power memory devices in the Big Data era. While polar configurations such as vortices, flux-closure domains, center-type domains, skyrmions, and merons have been extensively explored, antivortices remain largely underdeveloped. In this work, the discovery and realization of stable polar vortex-antivortex pair arrays within multiferroic-dielectric superlattices are reported with integrated experimental and theoretical efforts, enabled by low-symmetry BiFeO3 with diagonal spontaneous polarization. By employing atomic-level engineering to precisely modulate the architecture of BiFeO3 layers, achieving unprecedented periodicities as small as 4.5 nm. These arrays exhibit exceptional thermal stability, preserving their structural integrity above room temperature, and reversible polarization switching under applied electric fields. Additionally, the sensitivity of domain wall configurations to the dielectric layer thickness offers further tunability. These findings not only expand the scope of ferroelectric topologies but also provide a versatile platform for harnessing antivortices in practical applications, paving the way for next-generation ultrahigh-density, low-power memory technologies.

Permanent magnetic thick films are increasingly used in Micro-Electro-Mechanical Systems (MEMS) devices, but the interplay between magnetic properties, microstructure, and film thickness remains underexplored. We deposited SmCo-based films with thicknesses ranging from 350 nm to 1300 nm using magnetron sputtering at room temperature, followed by in-situ annealing. Our study examined the evolution of microstructure, phase composition, magnetic properties, and domain structures as thickness increases. The films displayed dense, fibrous structures typical of the zone T-type region, with 3D morphologies forming a network structure and an arc-shaped surface that expands with thickness. At thinner levels (around 350 nm), an amorphous SmCo phase predominates, prone to oxidation, while at greater thicknesses, the SmCo5 phase dominates but maintains a grain size of 12-15 nm. Coercivity decreases significantly from 33 kOe to 8 kOe as thickness increases from 630 to 1300 nm due to the diminishing pinning effect and dominance of the reversal domain nucleation mechanism. Analysis using magnetic force microscopy and micromagnetic simulations indicates that this reduction in coercivity is mainly due to the decomposition of the SmCo5 phase and a reduction in magnetic domain size.

Ferroelectric domain walls (FDWs) exhibit exotic structural and electronic properties, positioning them as a promising functional element for next-generation nanoelectronics. However, achieving the deterministic creation of FDWs with nanoscale precision and controlled polarization of domains remains a substantial challenge for the scalable FDW-device fabrication and circuit design. Here, we demonstrate a strategy for FDW engineering by tailoring the interfacial electrostatic profile. Using SrRuO3 islands as "nano-masks," we spatially modulate the interfacial atomic termination to generate alternating positive and negative built-in electric fields. The boundaries where the electric field switches polarity drive the formation of 180° FDWs in BiFeO3 thin films. This mechanism is validated through theoretical calculations and direct experimental observations. Furthermore, atomic-scale analysis reveals localized lattice distortions, structural chirality of the FDWs, as well as the edge effect of SrRuO3 islands on the position precision of FDW nucleation. Our findings pave the way toward a scalable and controllable bottom-up FDW-growth technique for future FDW nanoelectronics.

Flexoelectric and photo-flexoelectricity are scientifically intriguing and hold considerable potential for various applications such as soft strain sensing, photovoltaics, energy harvesting, etc. Among flexoelectric materials, freestanding ferroelectric thin films are believed to have huge flexoelectricity and tunability due to their excellent lattice regulatory freedom and sustainability to larger strain gradients. In this work, we demonstrated a freestanding BiFeO3(BFO) thin film-based soft strain sensor and explored their flexoelectric coefficient and flexoelectric photovoltaic effect under different strain gradients. Under different bending scales, the photocurrent of the thin film exhibits a step-like variation, indicating that the sensor can measure strain gradient with high sensitivity. These results show the potential application of freestanding ferroelectric films in flexible devices.

The coupling structure that integrates both hierarchical super-structures and polar topology is anticipated to generate exceptional performance characteristics due to their synergic effect. However, fabricating large-area arrays of stable hierarchical center-type topologies at the nanoscale remains a considerable challenge. Here, by employing a unique interfacial build-in field mechanism, we achieved a breakthrough in the large-scale synthesis of stable hierarchic center-type patterns derived from dimensionally confined topologically trivial PbTiO3 (PTO) a1/a2 superdomains. Through nanoscale piezoresponse force microscopy (PFM) and scanning transmission electron microscopy (STEM), the fine domain structures can be clearly delineated, exhibiting distinct four-quadrant textures with charged domain walls appearing at quadrant boundaries, alone with high piezoresponse a/c domains in the central regions. These hierarchic center-type configurations are spontaneously formed and remain stable over several months. Specifically, these domains can also be modulated by either external field or variation nanoislands height, while can be recovered by heating at elevated temperature. These findings provide unique insights into the formation mechanism of hierarchic topological structures and open up potential applications in nano-electromechanical systems, piezotronics, and topological electronics.

Flexible and transparent optoelectronic technology has shown great application prospects in various fields. Introducing rare earth luminescent centers into inorganic ferroelectric systems can benefit the electrical properties by utilizing the polar nanodomains brought about by rare earth doping and also facilitate the investigation of coupling effect between luminescence modulation and flexoelectric effect. This article studies Pr3+-doped barium titanate all-inorganic flexible transparent heterojunctions and explores the direct modulation of the fluorescence and flexoelectric response through mechanical strain stimulation. We aim to investigate the essential correlation and physical mechanism of strain-flexoelectricity-photoluminescence (force-electric-photon) coupling, providing an important basis for the dynamic balance regulation between radiative and non-radiative transitions. Therefore, this work will significantly promote the development of highly integrated flexible sensing and intelligent optoelectronic devices.

Ferroelectric oxides have attracted considerable attention due to their unique intrinsic properties, such as spontaneous polarization and high dielectric constants, which make them promising candidates for nonvolatile memory devices, electrostrictive actuators, and sensors. However, integrating ferroelectric oxides with silicon remains a significant challenge, hindering their widespread use in nanoelectronic devices. Here, we introduce a fully strain-relaxed boost layer that functions as a pseudo-substrate, enabling the integration of multiferroic mixed-phase BiFeO3 (BFO) on silicon. This boost layer not only overcomes the limitations of traditional single-crystal oxide substrates by providing a strain platform but also facilitates the stabilization of BFO mixed phases through strain engineering. Additionally, we demonstrate that an external electric field can reversibly switch between these two phases and toggle between distinct polarization states. These results highlight a strain-engineering strategy that advances ferroelectric oxide integration with semiconductor platforms, paving the way for scalable and cost-effective device applications.

Tensile biaxial strain has been demonstrated to induce in-plane ferroelectricity in SrTiO3 thin films at room temperature. However, out-of-plane ferroelectricity is more favorable for electronic device applications. Here, we report the achievement of room-temperature out-of-plane ferroelectric SrTiO3 thin films with giant tetragonality (c/a ∼ 1.061) and an ultrahigh ferroelectric stablity temperature (>1000 K) through epitaxial strain and defect engineering. Optical second-harmonic generation (SHG) proves that the enhancement of tetragonality enables improved ferroelectricity. Moreover, a combination of scanning transmission electron microscopy (STEM) and X-ray absorption near-edge spectroscopy (XANES) reveals the origin of enhanced tetragonality and strong ferroelectricity in defect- and strain-codriven supertetragonal SrTiO3 thin films. Our findings present an approach to material design that can be extended to other material systems for the enhancement of ferroelectricity and the observation of emergent phenomena.

SmCo based films with excellent intrinsic magnetic properties have promising applications in microelectro-mechanical system (MEMS). However, due to the complexity of phase composition and uncontrollable crystallization degree of SmCo hard magnetic phase in the film, both the coercivity (Hc) and remanence (Mr) of films are difficult to enhance simultaneously. In this paper, SmCo based films were deposited with a Cr underlayer and capping layer on single crystal Si substrates via magnetron sputtering process. The effects of annealing parameters and Sm/Co atomic ratio on the phase structure and coercivity of films are discussed. By adjusting the Sm/Co atomic ratio from 1:5 to 1:4, Co soft magnetic phase disappears and the single phase SmCo5 is obtained, leading to the increase of coercivity of the films from 30 to 34 kOe. The influence of deposition temperature and Cu doping on magnetic properties of SmCo based films was investigated. When the deposition temperature increases from room temperature to 250 degrees C, the coercivity will further increase from 34 to 51 kOe. However, a severe kink is observed in the demagnetization curves due to the poor exchanged coupling. An analysis of transmission electron microscopy (TEM) confirms that the average size of non-hard magnetic amorphous phase exceeds the effective exchanged coupling length of SmCo5, which contributes to the decoupling and low remanence ratio. Therefore, doping Cu and applying a post-annealing process can significantly improve the crystallization degree of the films. Both the coercivity and the remanence ratio of the demagnetization curves are greatly enhanced. We propose a plausible strategy to prepare the SmCo based films with high coercivity and remanence ratio by temperature and chemical optimization, which can be utilized in high performed MEMS devices. (c) 2023 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights are reserved, including those

Lead-free dielectric ceramic capacitors are attracting much interest in pulse power systems owing to their fast charge/discharge rate and high power density. However, their development towards integration and miniatur-ization in electronic devices has been severely impeded by low energy storage performance (ESP) under low electric field (E). Herein, a synergistic optimization strategy of composition design and domain engineering was proposed in the Bi(Mg0.5Hf0.5)O3-modified Na0.5Bi0.5TiO3-Sr0.7Bi0.2Ca0.1TiO3 ceramics [(1-x)(NBT-SBCT)-xBMH], aiming to improve ESP at low E. As a result, an ultrahigh recoverable energy density (Wrec) of-5.9 J/ cm3 and a high efficiency (eta) of-85 % can be obtained in x = 0.20 ceramics under a low E of 260 kV/cm, which is superior to previously reported lead-free materials under the equivalent E. The outstanding Wrec is mainly ascribed to the ultrahigh polarization discrepancy (Delta P) of-50.8 mu C/cm2 since the rich hybridization of Bi 6 s and O 2p orbitals maintains a maximum polarization and the addition of Mg2+ and Hf4+ transforms the long-range ferroelectric order into polar nanoregions (PNRs) with good relaxation characteristics. Moreover, a fast discharge time (-62 ns), good temperature (20-120 degrees C) and frequency (1-103 Hz) stabilities, and excellent fatigue resistance (x105 cycles) can be concurrently realized in x = 0.20 ceramics. These results demonstrate the promising strategy of developing low E lead-free ceramics for dielectric energy storage.

Magnon frequency comb provides opportunities for exploring magnon nonlinear effects and measuring the transmission magnon frequency in magnets, whose controllability becomes vital for modulating the operating frequency and improving the measurement accuracy. Nevertheless, such controllable frequency comb remains to be explored. In this work, we investigate theoretically and numerically the skyrmion-induced magnon frequency comb effect generated by interaction between the magnon excitation mode and skyrmion breathing mode in synthetic ferrimagnets. It is revealed that both the skyrmion breathing mode and the magnon frequency gap closely depend on the net angular momentum {\delta}s, emphasizing the pivotal role of {\delta}s as an effective control parameter in governing the comb teeth. With the increase of {\delta}s, the skyrmion size decreases, which results in the enlargement of the breathing frequency and the distance between the comb teeth. Moreover, the dependences of the magnon frequency gap on {\delta}s and the inter-layer coupling allow one to modulate the comb lowest coherent frequency via structural control. Consequently, the coherent modes generated by the comb may range from gigahertz to terahertz frequencies, serving as a bridge between microwave and terahertz waves. Thus, this work represents a substantial advance in understanding the magnon frequency comb effect in ferrimagnets.

NaNbO3 (NN)-based ceramics have received a great deal of attention for the potential application in dielectric energy storage capacitors. However, the energy storage properties (ESP) remain low, particularly under moderate electric field. Herein, a Bi-rich doping unit of BiMg2/3Nb1/3O3 (BMN) was introduced into a 0.85NaNbO(3)-0.15Bi(0.1)Sr(0.85)TiO(3) (NN-SBT) matrix, aiming to improve polarization along ESP. As a result, a large recoverable energy density (W-rec) of similar to 6.1 J/cm(3) and an efficiency (eta) of similar to 81 % were achieved in NN-SBT-0.08BMN ceramics under a moderate electric field of 337 kV/cm. The improved ESP can be attributed to the introduction of BMN, which delays the polarization saturation of NN-SBT ceramics, while maintaining the maximum polarization (similar to 43.6 mu C/cm(2)), and generating polar nanoregions (PNRs). Moreover, the optimal ceramics exhibited good thermal (25-130 degrees C) and frequency (1-300 Hz) stabilities, and fatigue endurance (>10(5) cycles). These results illustrate that the designed NN-SBT-0.08BMN ceramics are promising for application in dielectric energy storage capacitors with high ESP under a moderate electric field.

In this work, we demonstrated that tunable topological domain structures, e.g., center-type domains and skyrmion-like polar bubbles, can be generated at room temperature in high-density epitaxial PbTiO3 nanodots fabricated via the template-assisted tailoring of thin films. These topological domain structures can be manipulated electrically by applying an appropriate bias on the conductive atomic force microscopy tip, allowing for writing, erasing, and rewriting of topological domains into the nanodot. Moreover, ring-shaped conductive channels are observed around the center-type domain states. These findings provide a playground for further exploring their emerging functionalities and application potentials for nanoelectronics.

Magnetic disclination, characterized by the orientation of domain-wall arrangement rotating by π along a closed loop, is a type of topological spin texture. This study demonstrates the creation of artificial magnetic disclination through local stress engineering. By patterning nanotrenches in permalloy/poly(methyl methacrylate) bilayers, the tensile stress is relieved in a directional manner through the formation of boundaries. This orients the domain distributions at the microscale through magnetoelastic coupling. Two-dimensional (2D) closed boundaries induce curved stripe domains, which are ultimately converted into disclinations. The geometric configuration and arrangement of the disclination can be spatially adjusted via 2D boundary designation. The combination of in-situ magnetic force microscopy and hysteresis loop measurements links the microscopic domain configuration to the macroscopic magnetic properties of the system. Simulations reveal that the magnetic disclination is critically dominated by the local stress distribution within the topographic confinement.

Permanent magnetic thick films are increasingly used in Micro-Electro-Mechanical Systems (MEMS) devices, but the interplay between magnetic properties, microstructure, and film thickness remains underexplored. We deposited SmCo-based films with thicknesses ranging from 350 nm to 1300 nm using magnetron sputtering at room temperature, followed by in-situ annealing. Our study examined the evolution of microstructure, phase composition, magnetic properties, and domain structures as thickness increases. The films displayed dense, fibrous structures typical of the zone T-type region, with 3D morphologies forming a network structure and an arc-shaped surface that expands with thickness. At thinner levels (around 350 nm), an amorphous SmCo phase predominates, prone to oxidation, while at greater thicknesses, the SmCo5 phase dominates but maintains a grain size of 12-15 nm. Coercivity decreases significantly from 33 kOe to 8 kOe as thickness increases from 630 to 1300 nm due to the diminishing pinning effect and dominance of the reversal domain nucleation mechanism. Analysis using magnetic force microscopy and micromagnetic simulations indicates that this reduction in coercivity is mainly due to the decomposition of the SmCo5 phase and a reduction in magnetic domain size.

Precise control of skyrmion dynamics is essential for the future spintronic device design based on the magnetic skyrmions. In this work, we propose a scheme to implement hybrid magnetic skyrmions (HMS) in ferrimagnets and we study the dynamics of the HMS driven by spin–orbit torque. It is revealed that the skyrmion Hall effect depends on the skyrmion helicity and the net angular momentum (δs), allowing the effective modulation of the HMS motion through tuning Dzyaloshinskii–Moriya interaction and δs. Moreover, the Magnus force for finite δs suppresses the transverse motion and enhances the longitudinal propagation, resulting in the decrease in Hall angle accompanying faster dynamics than that in antiferromagnets. Thus, the Hall effect can be suppressed through selecting suitable materials to better control the HMS motion. Finally, we propose a convenient skyrmion diversion scheme through modulating the helicity and Hall angle of the HMS, benefiting the future spintronic device design.

Herein, novel binary systems of (1-x)Ba0.85Ca0.15Zr0.1Ti0.9O3-xBi(Mg0.5Hf0.5)O3 ((1-x)BCZT-xBMH, x = 0.00 0.30) were fabricated based on a collaborative optimization strategy of compositional modulation and nano domain. All the samples have a pure perovskite structure with a compact microstructure devoid of pores. Interestingly, an excellent recoverable energy density (Wrec 3.29 J/cm3) and high efficiency (eta 90%) were achieved in 0.75BCZT-0.25BMH ceramics under 305 kV/cm. The improved energy storage performances (ESP) could be attributed to the fact that the introduction of Bi(Mg0.5Hf0.5)O3 increases the band gap, decreases the leakage current and grain size, in particular, frustrates the long range ferroelectric order, leading to the formation of the polar nanoregions (PNRs). Moreover, an ultrahigh power density (-133.76 MW/cm3), an ultrafast discharge time (-98 ns), an high frequency stability (1-103 Hz), fatigue resistance (x104 cycles), and good temperature stability (20-120 degrees C) can be concurrently realized in the optimized ceramics. These results demonstrate that the environmentally friendly 0.75BCZT-0.25BMH lead-free ceramics are a potential candidate for dielectric energy storage devices.

Compared to electrochemical energy storage, dielectric thin film-based capacitors possess the advantages of higher voltage stability and higher break-down voltage as well as lower leakage current etc. Since HfO2 films are compatible to microelectronic process and its ferroelectricity is strategically important in memory device, the realization of their excellent energy storage performance will broaden their applications in microelectronic devices. In this study, we utilized Al3+ dopant, known for its smaller ionic radius compared to Hf4+, to induce lattice disorder in the Hf0.5Zr0.5O2 films, facilitating transformation of the Hf0.5Zr0.5O2 film from ferroelectric to antiferroelectric, and ultimately to a superparaelectric-like relaxation antiferroelectric behaviors. We have experimentally demonstrated that, by introduction of an appropriate Al doping level of x = 4.13%, the Hf0.5Zr0.5O2 thin films with a relaxor antiferroelectric characteristic can achieve a corresponding recoverable energy density of more than 100 J cm(-3), an efficiency of more than 80%, and an effective enhancement of the dielectric strength to more than 6 MV cm(-1). Compared to HfO2-based amorphous/crystalline films reported previously, this is a record-high energy density in atomic layer deposited HfO2/ZrO2 ternary doped oxides, and beyond that, we also demonstrate their superfast charging/discharging as a capacitor. Targeting at high-speed supercapacitor applications in integrated circuit, HfO2-based dielectric may win the competition with perovskite oxides in terms of dielectric breakdown strength and charging/discharging speed etc. Our fundamental understanding of the physics behind also enriches the knowledge of materials science and dielectric physics.