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Abstract Controlling the direction of ferromagnetism and antiferromagnetism by an electric field in single-phase multiferroics will open the door to the next generation of devices for spintronics and electronics. The typical magnetoelectric coupling such as the linear magnetoelectric effect is very weak in type-I multiferroics and therefore the magnetoelectric switching is rarely achieved. Here, using first-principles simulations, we propose a magnetoelectric switching mechanism to achieve such highly desired control in orthorhombic multiferroics. One class of two-dimensional proper multiferroics (CrX 2Se3 and MnX 2Te3, X = Sn, Ge) and perovskite multiferroics (EuTiO3 and BiFeO3/LaFeO3 superlattice) are taken as examples to show the mechanism. In the ferroelectric switching process, the proper polarization rotates its direction by 180° and keeps its magnitude almost unchanged, the ferromagnetic or antiferromagnetic vector is rotationally switched by 180° following the rotation of ferroelectric polarization. This rotational magnetoelectric switching results from in-plane structural anisotropy and magnetic anisotropy, and the process of switching is governed by c o s i n e functions from the phenomenological Landau-type models. This study addresses the challenge of magnetoelectric switching in type-I multiferroics by proposing a general magnetoelectric switching mechanism.

Abstract Piezoelectrics are a class of functional materials that have been extensively used for application in modern electro-mechanical and mechatronics technologies. The sign of longitudinal piezoelectric coefficients is typically positive but recently a few ferroelectrics, such as ferroelectric polymer poly(vinylidene fluoride) and van der Waals ferroelectric CuInP2S6, were experimentally found to have negative piezoelectricity. Here, using first-principles calculation and measurements, we show that the sign of the longitudinal linear piezoelectric coefficient of HfO2 can be tuned from positive to negative via epitaxial strain. Nonlinear and even parabolic piezoelectric behaviors are further found at tensile epitaxial strain. This parabolic piezoelectric behavior implies that the polarization decreases when increasing the magnitude of either compressive or tensile longitudinal strain, or, equivalently, that the strain increases when increasing the magnitude of electric field being either parallel or antiparallel to the direction of polarization. The unusual piezoelectric effects are from the chemical coordination of the active oxygen atoms. These striking piezoelectric features of positive and negative sign, as well as linear and parabolical behaviors, expand the current knowledge in piezoelectricity and broaden the potential of piezoelectric applications towards electro-mechanical and communications technology.

Abstract The deterministic creation and modification of domain walls in ferroelectric films have attracted broad interest due to their unprecedented potential as the active element in non-volatile memory, logic computation and energy-harvesting technologies. However, the correlation between charged and antiphase states, and their hybridization into a single domain wall still remain elusive. Here we demonstrate the facile fabrication of antiphase boundaries in BiFeO3 thin films using a He-ion implantation process. Cross-sectional electron microscopy, spectroscopy and piezoresponse force measurement reveal the creation of a continuous in-plane charged antiphase boundaries around the implanted depth and a variety of atomic bonding configurations at the antiphase interface, showing the atomically sharp 180° polarization reversal across the boundary. Therefore, this work not only inspires a domain-wall fabrication strategy using He-ion implantation, which is compatible with the wafer-scale patterning, but also provides atomic-scale structural insights for its future utilization in domain-wall nanoelectronics.

Memristive neural networks have extensively been investigated for their capability in handling various artificial intelligence tasks. The training performance of memristive neural networks depends on the pulse scheme applied to the constituent memristors. However, the design of the pulse scheme in most previous studies was approached in an empirical manner or through a trial-and-error method. Here, we choose ferroelectric tunnel junction (FTJ) as a model memristor and demonstrate a physics-based predictive model for the pulse design to achieve high training performance. This predictive model comprises a physical model for FTJ that can adequately describe the polarization switching and memristive switching behaviors of the FTJ and an FTJ-based neural network that uses the long-term potentiation (LTP)/long-term depression (LTD) characteristics of the FTJ for the weight update. Simulation results based on the predictive model demonstrate that the LTP/LTD characteristics with a good trade-off between ON/OFF ratio, nonlinearity, and asymmetry can lead to high training accuracies for the FTJ-based neural network. Moreover, it is revealed that an amplitude-increasing pulse scheme may be the most favorable pulse scheme as it offers the widest ranges of pulse amplitudes and widths for achieving high accuracies. This study may provide useful guidance for the pulse design in the experimental development of high-performance memristive neural networks.

The controllable manipulation of polar topological structures (e.g. skyrmion bubble) in ferroelectric materials have been considered as a cornerstone for future programmable nano-electronics. Here, we present the effective creation and erasure of polar bubble states PbTiO3 (PTO) multilayers trigged by mechanical stress and light illumination, respectively. It was found that applying atomic force microscope (AFM) tip force can induced formation of nanoscale bubble domains from the initial monodomain state. Moreover, the created bubble domain can be eliminated by exposure to ultraviolet or infrared light illumination. The above results can be understood by modulation of depolarization screening charges and bias fields, as reflected by scanning Kelvin potential microscopic (SKPM) observations, whereby the flexoelectric effect from the tip force tends to remove the screening charges on top surface and modulate the bias field that favors the formation of bubble state while light illumination tends to recover the screen charges and favor the monodomain state. The results provide a good example for multi-field manipulation of polar topologies, which might create a new avenue towards the immerging new concept electronic devices.

Abstract Reservoir computing (RC) offers efficient temporal information processing with low training cost. All-ferroelectric implementation of RC is appealing because it can fully exploit the merits of ferroelectric memristors (e.g., good controllability); however, this has been undemonstrated due to the challenge of developing ferroelectric memristors with distinctly different switching characteristics specific to the reservoir and readout network. Here, we experimentally demonstrate an all-ferroelectric RC system whose reservoir and readout network are implemented with volatile and nonvolatile ferroelectric diodes (FDs), respectively. The volatile and nonvolatile FDs are derived from the same Pt/BiFeO3/SrRuO3 structure via the manipulation of an imprint field (E imp). It is shown that the volatile FD with E imp exhibits short-term memory and nonlinearity while the nonvolatile FD with negligible E imp displays long-term potentiation/depression, fulfilling the functional requirements of the reservoir and readout network, respectively. Hence, the all-ferroelectric RC system is competent for handling various temporal tasks. In particular, it achieves an ultralow normalized root mean square error of 0.017 in the Hénon map time-series prediction. Besides, both the volatile and nonvolatile FDs demonstrate long-term stability in ambient air, high endurance, and low power consumption, promising the all-ferroelectric RC system as a reliable and low-power neuromorphic hardware for temporal information processing.

Abstract The van der Waals (vdW) ferromagnet Fe3‐δGeTe2 has garnered significant research interest as a platform for skyrmionic spin configurations, that is, skyrmions and skyrmionic bubbles. However, despite extensive efforts, the origin of the Dzyaloshinskii–Moriya interaction (DMI) in Fe3‐δGeTe2 remains elusive, making it challenging to acquire these skyrmionic phases in a controlled manner. In this study, it is demonstrated that the Fe content in Fe3‐δGeTe2 has a profound effect on the crystal structure, DMI, and skyrmionic phase. For the first time, a marked increase in Fe atom displacement with decreasing Fe content is observed, transforming the original centrosymmetric crystal structure into a non‐centrosymmetric symmetry, leading to a considerable DMI. Additionally, by varying the Fe content and sample thickness, a controllable transition between Néel‐type skyrmions and Bloch‐type skyrmionic bubbles is achieved, governed by a delicate interplay between dipole–dipole interaction and the DMI. The findings offer novel insights into the variable skyrmionic phases in Fe3‐δGeTe2 and provide the impetus for developing vdW ferromagnet‐based spintronic devices.

The poor contact at poly(3-hexylthiophene)/perovskite interface has led to unsatisfactory performance in solar cells. To resolve this issue, the authors introduce a molecular bridge to form a charge transport channel, realizing devices with maximum efficiency value of 22.87% and long-term stability.

Spiking neural network (SNN) consisting of memristor-based artificial neurons and synapses has emerged as a compact and energy-efficient hardware solution for spatiotemporal information processing. However, it is challenging to develop memristive neurons and synapses based on the same material system because the required resistive switching (RS) characteristics are different. Here, it is shown that SrFeOx (SFO), an intriguing material system exhibiting topotactic phase transformation between insulating brownmillerite (BM) SrFeO2.5 phase and conductive perovskite (PV) SrFeO3 phase, can be engineered into both neuronal and synaptic devices. Using a BM-SFO single layer as the RS medium, the Au/BM-SFO/SrRuO3 (SRO) memristor exhibits nonvolatile RS behavior originating from the formation/rupture of PV-SFO filaments in the BM-SFO matrix. By contrast, using a PV-SFO (matrix)/BM-SFO (interfacial layer) bilayer as the RS medium, the Au/PV-SFO/BM-SFO/SRO memristor exhibits volatile RS behavior originating from the interfacial BM-PV phase transformation. Synaptic and neuronal characteristics are further demonstrated in the Au/BM-SFO/SRO and Au/PV-SFO/BM-SFO/SRO memristors, respectively. Using the SFO-based synapses and neurons, fully memristive SNNs are constructed by simulation, which show good performance on unsupervised image recognition. Our study suggests that SFO is a versatile material platform on which both neuronal and synaptic devices can be developed for constructing fully memristive SNNs.

Recently, there is a surge of research interest in configurable ferroelectric conductive domain walls which have been considered as possible fundamental building blocks for future electronic devices. In this work, by using piezoresponse force microscopy and conductive atomic force microscopy, we demonstrated the controlled manipulation of various conductive domain walls in epitaxial BiFeO3 thin films, e.g. neutral domain walls (NDW) and charged domain walls (CDWs). More interestingly, a specific type of nanoscale domains was also identified, which are surrounded by highly conductive circular CWDs. Similar nanoscale domains can also be controlled created and erasured by applying local field via conductive probe, which allow nondestructive current readout of different domain states with a large on/off resistance ratio up to 102. The results indicate the potential to design and develop high-density non-volatile ferroelectric memories by utilizing these programable conductive nanoscale domain walls.

As a high-k material, hafnium oxide (HfO2) has been used in gate dielectrics for decades. Since the discovery of polar phase in Si-doped HfO2 films, chemical doping has been widely demonstrated as an effective approach to stabilize the ferroelectric phase in HfO2 based thin films. However, the extra capping layer deposition, post-growth annealing and wake-up effect are usually required to arouse the ferroelectricity in HfO2 based thin films, resulting in the increase of complexity for sample synthesis and the impediment of device application. In this study, the ferroelectricity is observed in non-capped dopant-free HfO2 thin films prepared by pulsed laser deposition (PLD) without post-growth annealing. By adjusting the deposited temperature, oxygen pressure and thickness, the maximum polarization up to 14.7 μC/cm2 was obtained in 7.4 nm-thick film. The fraction of orthorhombic phase, concentrations of defects and size effects are considered as possible mechanisms for the influences of ferroelectric properties. This study indicates that PLD is an effective technique to fabricate high-quality ferroelectric HfO2 thin films in the absence of chemical doping, capping layer deposition and post-growth annealing, which may boost the process of nonvolatile memory device application.

Robust, fast, and low-power hardware platforms are desirable for the implementation of real-time machine vision. Here the authors develop a computing-in-sensor network using ferroelectric photo sensors with remanent-polarization-controlled photo responsivities.

Abstract Recently lead halide perovskite based solar cells have rapidly advanced and their power conversion efficiency (PCE) increased to 25.7%. The progress has been attributed to the super‐long carriers’ lifetime (τ) and long diffusion length (LD) of the photocarriers, however it has been a challenge to precisely characterize and understand the super‐long τ and LD of photocarriers. Here, a MAPbI3 single crystal exhibits four different τ which increase with LD extending from nm scale to mm scale. The prior two lifetimes estimated by transient photoluminescence (TPL) spectra are in the range of ns which comes from the recombination of photocarriers in the tens of nm thick surface layer. In contrast, the third lifetime estimated by transient open‐circuit voltage is hundreds of µs, which is a result of the excess photocarriers diffusing hundreds of µm to electrodes. Finally, the fourth lifetime estimated from the transient photoconductance is as long as sub‐second since the low‐density photocarriers under an electric field drift across the mm‐scale high‐quality single crystal. This study not only clarifies the physical mechanisms of four different lifetimes of photocarriers but also facilitates the design of novel electronics with the halide perovskite semiconductors.

Magnetoelectric (ME) materials have caught worldwide attentions owing to their potential technological applications in ME switching devices or high-density data storage. However, realizing a sufficiently strong ME effect in one single material is always the key issue. Herein, we systematically investigate the Co3NiNb2O9, including the characterization of its crystalline structure, magnetism, specific heat, and pyroelectric properties. It is revealed that Co3NiNb2O9 exhibits a remarkable ME response below the magnetic phase transition temperature of TN ∼32 K. On one hand, the magnetic field-induced electric polarization is observed below TN while it is non-ferroelectric at no magnetic field. The evaluated ME coefficient is as large as 21.2 ps/m. On the other hand, the magnetization is significantly modulated by the applied electric field, with the inverse ME coefficient being 14.1 ps/m. The observed ME responses suggest a stable ME mutual control by the magnetic or electric field in Co3NiNb2O9.

Ferroelectric tunnel junction (FTJ) has attracted considerable attention for its potential applications in nonvolatile memory and neuromorphic computing. However, the experimental exploration of FTJs with high ON/OFF ratios is a challenging task due to the vast search space comprising of ferroelectric and electrode materials, fabrication methods and conditions and so on. Here, machine learning (ML) is demonstrated to be an effective tool to guide the experimental search of FTJs with high ON/OFF ratios. A dataset consisting of 152 FTJ samples with nine features and one target attribute (i.e., ON/OFF ratio) is established for ML modeling. Among various ML models, the gradient boosting classification model achieves the highest prediction accuracy. Combining the feature importance analysis based on this model with the association rule mining, it is extracted that the utilizations of {graphene/graphite (Gra) (top), LaNiO3 (LNO) (bottom)} and {Gra (top), Ca[Formula: see text]Ce[Formula: see text]MnO3 (CCMO) (bottom)} electrode pairs are likely to result in high ON/OFF ratios in FTJs. Moreover, two previously unexplored FTJs: Gra/BaTiO3 (BTO)/LNO and Gra/BTO/CCMO, are predicted to achieve ON/OFF ratios higher than 1000. Guided by the ML predictions, the Gra/BTO/LNO and Gra/BTO/CCMO FTJs are experimentally fabricated, which unsurprisingly exhibit [Formula: see text]1000 ON/OFF ratios ([Formula: see text]8540 and [Formula: see text]7890, respectively). This study demonstrates a new paradigm of developing high-performance FTJs by using ML.

BiFeO3, a single-phase multiferroic material, possesses several polymorphs and exhibits a strong sensitivity to strain. Recently, emergent strain engineering in BiFeO3 thin films has attracted intense interest, which can overcome the confines of traditional strain engineering introduced through the mismatch between the film and substrate. In this review, we discuss emerging non-traditional strain engineering approaches to create new ground states and manipulate novel functionalities in multiferroic BiFeO3 thin films. Through fabricating freestanding thin films, inserting an interface layer or utilizing thermal expansion mismatch, continuously tunable strain can be imposed beyond substrate limitations. Nanostructured evolution and defect introduction are discussed as efficient routes to introduce strain, promising for the development of new nanodevices. Ultrafast optical excitation, growth conditions and chemical doping driven strain are summarized as well. We hope this review will arouse the readers’ interest in this fascinating field.

Memristor crossbar is extensively investigated as an energy‐efficient accelerator for neural network (NN) computations. However, hardware implementation of NNs using realistic memristors is challenging due to the ubiquity of faults (mainly classified into hard and soft faults) in memristors. Herein, a hardware‐friendly, low‐power multifault‐tolerant training (MFTT) scheme capable of addressing both hard and soft faults simultaneously for memristive NNs is proposed. The MFTT scheme consists of multifault detection, targeted weight pruning, and in situ training with the Manhattan update rule. Specifically, multifault detection is first conducted to detect both hard and large soft faults. The detected faulty weights are subsequently pruned to prevent them from disturbing the NN. The sparsified NN after pruning is in situ trained so that the hard and large soft faults can be effectively tolerated using the sparsity and self‐adaptivity of NNs. In addition, the remaining small soft faults can be well tolerated by the Manhattan update rule. Experimentally, MFTT demonstrates the lowest accuracy losses among several representative fault‐tolerant schemes not only in the hard fault‐only (when the hard fault ratio exceeds 10%) and soft fault‐only (when the soft faults are large) cases, but also in the case where both types of faults coexist.

Abstract Halide perovskite single crystal (HPSC) films have demonstrated extraordinary performance in solar cells, photodetectors, and lighting applications, owing to the high carrier mobility, long carrier diffusion length, tunable bandgap, and large light absorption coefficients of these materials. Here, the recent development of the major HPSC thin films is reviewed systematically, including MAPbI3, α‐FAPbI3, MAPbBr3, CsPbBr3, with special emphasis on different classes of fabrication methods and thin‐film characteristics. Finally, the conclusion and prospects in this field are discussed in detail. It is anticipated that the HPSC thin films will lead to a compelling future for the rising electronic applications.

Ferroelectric topological defects show emerging exotic physical properties, which are important for future nanoelectronic devices. Here, the authors demonstrate conductive metallic conduction channels in two types of topological defects, namely vortex and center cores.

The distinct spin amplitude wave was reported in a highly frustrated magnetic compound Fe _2 GeO _4 , which is very different from observations on other members of the M _2 GeO _4 (M = Fe, Co, and Ni) family, raising interest in this compound for some additional emergent phenomena. In particular, this non-uniform spin order allows the intrinsic connection between ferroelectric polarization and magnetically gradient structure to probe the potential linear magnetoelectric (ME) effect. In this work, we address this issue and investigate the magnetism of Fe _2 GeO _4 single crystal that hosts two successive anomalies at antiferromagnetic (AFM) Néel temperatures T _N1 ∼ 7.5 K and T _N2 ∼ 6.7 K, respectively. Our results reveal a remarkable metamagnetic transition in the magnetization as a function of the magnetic field, occurring at a critical magnetic field H _c ∼ 4.1 T when applied along the [110] and [1–10] directions, while such transition along the [001] direction is pointedly absent. Further exploration uncovers two predominant off-diagonal ME coefficients α _yz and α _zy in the incommensurate AFM phase between T _N1 and T _N2 . Additionally, all components of the linear ME tensor remain non-vanishing in the canting AFM phase below T _N2 . This indicates the ME mechanisms for the two phases that may be driven by different magnetic structures. All these presented results are sufficient for us to draw a non-trivial ME phase diagram, which is beneficial to understanding the ME behavior of Fe _2 GeO _4 . Therefore, our study implies that Fe _2 GeO _4 , an unusual frustrated magnet, provides a platform for manipulating the fascinating ME effect in the spinel structure.

Many perovskite oxide ferroelectrics (e.g. PbZr1-xTixO3, BaTiO3, LiNbO3) are born with multitudinous robust performances and have been widely used in sensors, actuators, surface acoustic wave devices, and memories et al. However, their hardness, brittleness and harsh synthesis conditions (i.e. high temperature and oxygen ambience) restrain their application into flexible electronic devices which are significant components among the three pillars of modern society development, i.e. energy, information and materials. Here we review the preparation of flexible devices based on these oxide ferroelectrics, including transferring these freestanding films to flexible substrates after separating ferroelectric oxide films from the hard substrates, such as Si and SrTiO3 crystals, and also direct fabrication methods without transferring process. Subsequently, we summarize three kinds of representative flexible devices, i.e. flexible ferroelectric memories, sensors and generators. These inorganic electronics not only show excellent electric properties competitive with those corresponding electronics on hard substrates but also exhibit good flexibility similar to many organic flexible electronics. Keywords: Perovskite oxides, Flexible devices, Sensors, Energy harvesters, Memories

Magnetic skyrmion in chiral magnet exhibits a variety of unique topological properties associated with its innate topological structure. This inspires a number of ongoing searching for new topological magnetic textures. In this work, we used micromagnetic simulations and Monte Carlo simulations to investigate an exotic Néel-type magnetic kinks in square-shaped nanostructures of chiral magnets, which performs rather stably in the absence of magnetic field. The individual magnetic kink can reside in one of the four possible corners, and carry possibly upward or downward core polarity, constituting eight degenerate states. In addition, these kinks also exhibit unique behaviors of generation, stability and dynamics, as revealed by micromagnetic simulations. It was found that such kinks can be created, annihilated, displaced, and polarity-reversed on demand by applying a spin-polarized current pulse, and are easily switchable among the eight degenerate states. In particularly, the kinks can be switched toward the ferromagnetic-like states and backward reversibly by applying two successive current pulses, indicating the capability of writing and deleting the kink structures. These findings predict the existence of Néel-type magnetic kinks in the square-shaped nanostructures, as well as provide us a promising approach to tailor the kinks by utilizing the corners of the nanostructures, and control these states by spin-polarized currents. The present work also suggests a theoretical guide to explore other chiral magnetic textures in nanostructures of polygon geometries.

The determination of the antiferromagnetic (AFM) orders by the anisotropic magnetoresistance (AMR) is one of the key components to the AFM-spintronics. Here the authors report enhanced AMR ~160% in Sr2IrO4 due to the combination of atomic scale giant-MR-like effect and magnetocrystalline anisotropy energy.

Abstract Flexible transparent conductive electrodes are essential component for flexible optoelectronic devices and have been extensively studied in recent years, while most of the researches are focusing on the electrode itself, few topics in material green and recyclability. In this paper, we demonstrate a high-performance transparent conductive electrode (TCE), based on our previous cracking technology, combined with a green and recyclable substrate, a starch film. It not only shows low R s (less than 1.0 Ω sq−1), high transparency (> 82%, figure of merit ≈ 10,000), but also provides an ultra-smooth morphology and recyclability. Furthermore, a series of biosensors on human joints are demonstrated, showing great sensitivity and mechanical stability.

Intelligent robots have assisted mankind in achieving and operating thousands of functions, especially with the arrival of the artificial intelligent. However, heat dissipation and thermal management in the intelligent robots remain big challenges, which limit their miniaturization and performance. Electrocaloric (EC) materials, which exhibit temperature change in response to the application or withdrawal of an electric field, open a new strategy for cooling technology and have gained a flurry of research interest in recent years. Toward artificial intelligent self-cooling electronic skins, large-scale flexible materials with high EC effect near room temperature are in demand. Here, we report a large room temperature EC effect in flexible Pb0.82Ba0.08La0.1Zr0.9Ti0.1O3 (PBLZT) inorganic thin films via a transfer-free cost-effective sol-gel process, assisted by unique two-dimensional mica substrates. The maximum adiabatic temperature change and isothermal entropy change of the flexible PBLZT thin films reach to 22.5 K and 25.9 J K− 1 kg− 1 at room temperature. In particular, the flexible PBLZT thin films exhibit a stable EC effect both under bending state and after bending for 20000 times. Our flexible EC materials offer an alternative strategy to the development of cooling technologies for both artificial intelligent robots and personal wearable cooling devices. Keywords: Electrocaloric effect, Ferroelectric thin film, Flexible electronics, Mica, Wearable device

Summary: Ferroelectric synapses using polarization switching (a purely electronic switching process) to induce analog conductance change have attracted considerable interest. Here, we propose ferroelectric photovoltaic (FePV) synapses that use polarization-controlled photocurrent as the readout and thus have no limitations on the forms and thicknesses of the constituent ferroelectric and electrode materials. This not only makes FePV synapses easy to fabricate but also reduces the depolarization effect and hence enhances the polarization controllability. As a proof-of-concept implementation, a Pt/Pb(Zr0.2Ti0.8)O3/LaNiO3 FePV synapse is facilely grown on a silicon substrate, which demonstrates continuous photovoltaic response modulation with good controllability (small nonlinearity and write noise) enabled by gradual polarization switching. Using photovoltaic response as synaptic weight, this device exhibits versatile synaptic functions including long-term potentiation/depression and spike-timing-dependent plasticity. A simulated FePV synapse-based neural network achieves high accuracies (>93%) for image recognition. This study paves a new way toward highly controllable and silicon-compatible synapses for neuromorphic computing.

Magnetic skyrmions are promising potential information carriers for future spintronic devices owing to their nanoscale size, non-volatility and high mobility. In this work, we demonstrate the controlled manipulation of skyrmion motion and its implementation in a new concept of racetrack logical device by introducing an inhomogeneous perpendicular magnetic anisotropy (PMA) via micromagnetic simulation. Here, the inhomogeneous PMA can be introduced by a capping nano-island that serves as a tunable potential barriers/well which can effectively modulate the size and shape of isolated skyrmion. Using the inhomogeneous PMA in skyrmion-based racetrack enables the manipulation of skyrmion motion behaviors, for instance, blocking, trapping or allowing passing the injected skyrmion. In addition, the skyrmion trapping operation can be further exploited in developing special designed racetrack devices with logic AND and NOT, wherein a set of logic AND operations can be realized via skyrmion–skyrmion repulsion between two skyrmions. These results indicate an effective method for tailoring the skyrmion structures and motion behaviors by using inhomogeneous PMA, which further provide a new pathway to all-electric skyrmion-based memory and logic devices.

Two-dimensional (2D) ferroelectrics refer to those ferroelectrics with layered structure and weak interlayer interactions (e.g., van de Waals interlayer coupling). A number of basic physical issues in the framework of ferroelectricity deserve clarifications, and one of them is the size effect regarding the dependence of ferroelectricity on material thickness. In this work, we investigate the ferroelectric domain structures of 2D ferroelectric CuInP2S6 nanoflakes attached on heavily doped Si wafers and polarization switching using the piezoresponse force microscopy. While the domain structure shows highly irregular morphology and 180° domain walls, the statistics on domain size (diameter) W and nanoflake thickness d demonstrates the remarkable thickness dependence of domain size, illustrated by the shrinking domain size from 630 nm to 75 nm with decreasing thickness d from ∼130 nm to ∼11 nm. This dependence fits the Landau-Lifshitz-Kittel (LLK) scaling law with the scaling exponent of ∼0.65, slightly larger than 0.5 for 3D ferroelectrics. It is suggested that the size effect in terms of the LLK scaling law does not show an essential difference between the 2D and 3D ferroelectric systems.

In photovoltaics window electrodes must display uniform current transport, as well as high light transmission from the substrate. Here, Han et al.show that quasi-fractal metallic networks provide a practical realization of an electrode structure with an optimal surface coverage and a uniform current density.

Voltage driven magnetic switching (VDMS) in multiferroic heterostructure is highly demanded for next generation energy efficient high-density memory (e.g. magnetoelectric random access memory) and spintronic devices. For practical applications in large scale integrated device, it is imperative to understand the VDMS behaviors in nanometer scale. In this work, we have investigated the effects of geometric and anisotropy parameters on 180° VDMS behaviors in a model multiferroic heterostructure system consisting of Co nano-ellipse on BiFeO3 films by using micromagnetic simulation. It was revealed that the switching behaviors can be greatly affected by geometric factors, whereby dimension shrinkage and rising aspect ratio of Co nano-ellipse can apparently increase the critical exchange coupling field (hDMcri-field) needed for triggering the VDMS, greatly reducing the watchability of VDMS. To improve the watchability, an external static perpendicular magnetoanisotropy (Kp) can be introduced to reduce the hDMcri-field, whereas too large Kp tends to reorientate the magnetization towards out-of-plane orientation. Moreover, a strategy was also proposed to assist the VDMS by applying an anisotropy pulse, which is able to reduce the hDMcri-field and expand the switching window (e.g. wider range of aspect ratio and overall dimension size) for both in-plane and out-of-plane VDMS. These results may provide some guides for further experimental modulation of VDMS for device applications.

Abstract A rapid surge in the research of lightweight, invisible, and flexible electronics is occurring with the arrival of Internet of Things (IoT). However, multifunctional perovskite oxide electronics are commonly hard and should be synthesized at high temperature and oxygen ambience, where most transparent conductive films will become brittle or highly resistive. Thus, the realization of transparent and flexible nonvolatile perovskite oxide resistive memory remains a big challenge. Here, a transparent, flexible, nonvolatile, and all‐inorganic memory with the mica substrate is prepared: the 2.7 wt% Ag‐doped indium–tin oxide (Ag–ITO) film as bottom electrodes, the BaTi0.95Co0.05O3−δ (BTCO) film as resistive‐switching functional layer, and the Ag/ITO films as top electrodes. The Ag–ITO/BTCO/Ag/ITO heterosturcture shows a unipolar resistive‐switching behavior, and its high/low resistance ratio is up to 5 × 103 under a low operating voltage (

Abstract Background Generation and regulation (control) of linear and angular momentum is a challenge during turning while walking which may be exacerbated by age-related changes. In healthy older adults, little is known about how momentum is controlled during turns, especially within each phase of gait. Each phase of gait affords unique mechanical contexts to control momenta and regulate balance. In healthy young adults, we found that the transverse-plane linear and angular momenta generation strategies observed within specific phases of gait during straight-line gait were also used during turns. Therefore, in this study, we investigated whether healthy older adults shared similar momentum control strategies specific to each gait phase during straight-line gait and turns. Methods Nine healthy older adults completed straight-line gait and 90° leftward walking turns. We compared the change in transverse-plane whole-body linear and angular momentum across gait phases (left and right single and double support). We also compared the average leftward force and transverse-plane moment across gait phases. Results We found that leftward linear momentum was generated most during right single support in straight-line gait and leftward turns. However, in contrast to straight-line gait, during leftward turns, average leftward force was applied across gait phases, with left single support generating significantly less leftward average force than other gait phases. Leftward angular momentum generation and average moment were greatest during left double support in both tasks. We observed some within-participant results that diverged from the group statistical findings, illustrating that although they are common, these momenta control strategies are not necessary. Conclusions Older adults generated transverse-plane linear and angular momentum during consistent phases of gait during straight-line gait and 90° turns, potentially indicating a shared control strategy. Understanding momentum control within each phase of gait can help design more specific targets in gait and balance training interventions.