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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. [ABSTRACT FROM AUTHOR]

Running jumps that depart the ground from two feet require momenta redirection upward from initial momenta that are primarily horizontal. It is not known how each leg generates backward and upward impulses from ground reaction forces to satisfy this mechanical objective when jumping to maximize height. We examined whole-body linear momentum control strategies during these two-foot running jumps by uncovering the roles of each leg in impulse generation. 3D motion capture and force plates were used to record 14 male basketball players performing two-foot running jumps towards an adjustable basketball hoop. Total ground contact phase started from the first leg ground contact and ended at takeoff and was divided into center of mass descent and ascent subphases. During the total ground contact phase, all participants generated significantly more upward impulse with the first leg and ten participants generated significantly more backward impulse with the first leg compared to the second leg. During the descent subphase, all participants generated significantly more upward and backward impulses with the first leg. During the ascent subphase, all but one participant generated significantly more backward impulse with the second leg. In addition to group-level statistics, participant-specific strategies were described. Overall, this study revealed the fundamental whole-body momentum control strategies used in two-foot running jumps and supports future research into optimal jump techniques and training interventions that respect the need to satisfy the mechanical objectives of the movement. [ABSTRACT FROM AUTHOR]

This study examined the roles of each leg in generating linear and angular impulses during baseball pitching. Professional pitchers (n = 4) pitched from a force plate instrumented mound, and 6–11 successful fastball pitches were used for analyses. We compared linear and angular impulses across the back and front legs. Linear and angular impulses were calculated from ground reaction force (GRF) and moment about each global axis passing through the centre of mass (COM), respectively. Additionally, we analysed measures that control the moment: (1) GRF magnitude, (2) magnitude of the position vector from COM to the centre of pressure and (3) the angle between (1) and (2). We found that the back leg generated forward linear impulse and the front leg generated backward linear impulse for all pitchers. Surprisingly, we found that the back leg generated significantly greater positive angular impulse about a global leftward axis (from the mound towards first base) than did the front leg in all four pitchers. Furthermore, the back leg’s moment about the leftward axis became positive after the magnitude of forward GRF decreased from its maximum, suggesting that the back leg’s role transitioned from generating forward linear momentum to angular momentum. [ABSTRACT FROM AUTHOR]

In the classical model, ferroelectricity is associated with small ion displacements from paraelectric phases with high symmetry, and ferroelectric crystals must adopt one of the ten polar point groups with low symmetry according to Neumann's principle. In this work, it is proposed that this conclusion is based on perfect bulk crystals without taking the boundaries into account. First‐principles evidence shows that ferroelectric polarizations may also be formed in some non‐polar point groups as the edges generally break the crystal symmetry. Meanwhile, such polarizations can be maintained at macroscale and are switchable when the transition between multiple equivalent states with high symmetry can be realized via long ion displacements， essentially akin to ion conductors. For example, the switching barriers can be much reduced in sliding ferroelectric bilayer systems or ionic compounds with covalent‐like directionality. Such unconventional ferroelectricity can be attributed to the boundaries and long ion displacements, and its existence in several systems like CuCrS2 is supported by experimental observations. It may explain a series of unclarified phenomena reported previously as well as significantly expand the scope of ferroelectrics, especially those with high polarizations induced by long ion displacements. [ABSTRACT FROM AUTHOR]

We describe the impact of post-annealing on ferroelectric-domain structures in arrays of BiFeO3 (BFO) epitaxial nanoislands, which exhibit a domain evolution from an initial 71° stripe/vortex domains to center-convergent topological domains. These results suggest that the increase and redistribution of charged defects, e.g., oxygen vacancies, in BFO nanoislands play a crucial role in driving the formation of center-type domain structures. The observation of defect-driven domain evolution in BFO nanoislands provides a path for further exploring their formation mechanism, topological properties, novel functionalities, and potential applications. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) van der Waals (vdW) magnets are believed to be promising candidates for next-generation information storage, which requires both high Curie points (TC) and large perpendicular magnetic anisotropy (PMA). As one of the most well-known 2D magnets, CrI3 has large PMA but a relatively low TC. Recent theoretical works proposed that implanting metal atoms into the hollow sites of CrI3 could greatly boost TC. However, this process may have the unintended consequence of reducing the PMA and introducing in-plane magnetic anisotropy (IMA) instead. It is, therefore, highly required to implement an additional technique to enhance the PMA. In this work, we use the first-principles method to study the underlying mechanisms of the suppressed PMA (and induced IMA) in the Co-implanted CrI3 monolayer [denoted as Co-(CrI3)2] as an example. It is found that the Co-implantation-induced itinerant electrons cause the transition from PMA to IMA by tuning the orbital orientation of the states around the Fermi level, noting that an in-plane (or out-of-plane) electronic orbital leads to the out-of-plane (or in-plane) momentum that favors PMA (or IMA) due to the spin–orbit coupling. In order to restore the PMA, we predict that using the vdW substrate PtTe2 to construct a heterostructure with the Co-(CrI3)2 monolayer not only reduces the contributions of the interfacial out-of-plane orbitals but also generates additional intralayer in-plane orbitals, both supporting the PMA. Thus, this work provides alternative perspectives on enhancing PMA by interfacial engineering of orbital orientation, paving the way for the development of 2D strong magnets. [ABSTRACT FROM AUTHOR]

It is known that rare-earth-based pyrochlore oxide may accommodate the well-defined two-in-two-out spin ice state with its tetrahedral unit. Low-energy excitation is argued to favor the highly concerned monopole state which attracts essential attention. However, such an excitation cannot be directly tracked and imaged using advanced characterizations, raising challenges to our understanding of the physics of monopoles. In this work, we propose an improved two-dimensional artificial spin ice structure on the Shastry–Sutherland lattice to restore the degeneracy of realistic pyrochlore systems. Such a structure avoids the deficiency of inequivalent nearest and next-nearest exchanges in the planar quadrate unit, which, however, is equivalent to the tetrahedral unit of realistic pyrochlore oxides. Therefore, this spin ice model restores state degeneracy that is lost in conventional planar artificial spin ice structures, representing an improved simulator of real spin ice systems. Our careful investigations of such improved structures reveal the rich physics of spin ice excitations, including the phase diagram, which allows different ordered phases and interesting critical phase transitions between spin ice phase I and phase II. Energy spectrum analysis suggests that restoration of state degeneracy substantially reduces monopole excitation energy, resulting in a striking monopole emergency at the critical point. Furthermore, the emergent spin dimer phase in this improved model allows high-density monopole excitations and exhibits high-correlated monopole fluid states. [ABSTRACT FROM AUTHOR]

Antiferromagnetic spintronics is intrigued due to its unique properties that could break through the restrictions in ferromagnets. A 3d/5d transition metal oxide heterostructure is a good platform in antiferromagnetic spintronics research since the strong spin–orbit coupling in 5d oxides may bring about delicate interaction with the correlation energy and motivate unconventional phenomena. Here, the transport and magnetic characters of bilayers composed of antiferromagnetic 3d perovskite NdNiO3 and 5d perovskite SrIrO3 were investigated. The decreased metal–insulator transition and Néel temperature associated with suppressed negative magnetoresistance, emerged spin-glass like phenomenon, and the humped nonlinear Hall effect were observed in NdNiO3/SrIrO3 bilayers, which were absent in NdNiO3 and SrIrO3 pure films. It suggests the important role of interfacial interaction between NdNiO3 and SrIrO3 in modulating heterostructure transport and magnetic behavior and also manifests that complex magnetic structures might be realized in NdNiO3/SrIrO3 bilayers. [ABSTRACT FROM AUTHOR]

Transition metal oxides provide opportunities to induce and modulate the superconducting state, due to the delicate interplay between charge, spin, orbital, and lattice order. In this work, 5d transition metal oxide SrTaO3 films were deposited by pulsed laser deposition, and an anomalous negative resistance was observed. The negative resistance can be ascribed to the nonuniform conductivity, associated with nonuniform electronic states in the SrTaO3 thin films, as confirmed by conductive atomic force microscopy and x-ray photoelectron spectroscopy. Moreover, a sharp drop in the resistance together with a decrease in magnetization was observed at around 40 K. This might imply a possible superconducting state. The negative resistance can be well explained based on an equivalent circuit comprising normal and superconductive states, also supporting the possible superconducting state in SrTaO3 thin films. This work promotes the exploring and revealing of the mechanism in tantalates superconductivity. [ABSTRACT FROM AUTHOR]

Multiferroics are those materials with more than one ferroic order, and magnetoelectricity refers to the mutual coupling between magnetism (spins and/or magnetic field) and electricity (electric dipoles and/or electric field). In spite of the long research history in the whole twentieth century, the discipline of multiferroicity has never been so highly active as that in the first decade of the twenty-first century, and it has become one of the hottest disciplines of condensed matter physics and materials science. A series of milestones and steady progress in the past decade have enabled our understanding of multiferroic physics substantially comprehensive and profound, which is further pushing forward the research frontier of this exciting area. The availability of more multiferroic materials and improved magnetoelectric performance are approaching to make the applications within reach. While seminal review articles covering the major progress before 2010 are available, an updated review addressing the new achievements since that time becomes imperative. In this review, following a concise outline of the basic knowledge of multiferroicity and magnetoelectricity, we summarize the important research activities on multiferroics, especially magnetoelectricity and related physics in the last six years. We consider not only single-phase multiferroics but also multiferroic heterostructures. We address the physical mechanisms regarding magnetoelectric coupling so that the backbone of this divergent discipline can be highlighted. A series of issues on lattice symmetry, magnetic ordering, ferroelectricity generation, electromagnon excitations, multiferroic domain structure and domain wall dynamics, and interfacial coupling in multiferroic heterostructures, will be revisited in an updated framework of physics. In addition, several emergent phenomena and related physics, including magnetic skyrmions and generic topological structures associated with magnetoelectricity will be discussed. The review is ended with a set of prospectives and forward-looking conclusions, which may inevitably reflect the authors' biased opinions but are certainly critical. [ABSTRACT FROM AUTHOR]

In recent few years, the two-dimensional (2D) magnets have emerged as one of the most important frontiers in materials physics and attracted much attention. As one of the earliest experimentally discovered 2D magnets, CrI3 shows a wealth of properties and has been extensively studied. In particular, an intriguing characteristic of the CrI3 monolayer is its octahedrally coordinated hollow within the unit-cell, which enables the implantation of a magnetic atom, thereby resulting in an artificial 2D superlattice with fertile physics to explore. In this work, using first-principles calculations, we investigate the Co-implanted CrI3 monolayer, denoted as Co-(CrI3)2, and demonstrate the vital roles of the exchange channels of eg electrons in enhancing magnetism. It is shown that the Co-(CrI3)2 monolayer has a half-metallic ferrimagnetic (FiM) ground-state with a net in-plane magnetic moment of 5.0μB/f.u. and a relatively high Curie point (TC) of ∼195 K, noting that TC of pristine CrI3 is only 45–61 K. The FiM ordering is established by the strong anti-ferromagnetic coupling in the t2g-eg exchange channels of the nearest-neighbor (NN) Cr–Co pair and the sizeable ferromagnetic coupling of the third NN Cr–Cr pair mediated by the itinerant eg electrons. In addition, an in-plane biaxial tensile strain of ∼2% may further enhance TC up to ∼210 K. This work offers unique insights into the magnetism enhancement of the CrI3 monolayer by atom-implantation, paving the way for the development of 2D magnets. [ABSTRACT FROM AUTHOR]

Emerging topological polar domains have a wide range of potential applications in electronic devices. It is critical to accurately manipulate these topological domains by electrical fields and explore their exotic properties for making more energy-efficient high-density non-volatile memories. Herein, we demonstrate that skyrmion-like polar nanodomains appear at room temperature in SrTiO3/PbTiO3 bilayer heterostructures by balancing the elastic and electrostatic energies via varying the SrTiO3 capping layer thickness. These polar nanodomains, stable at room temperature, can be electrically written, erased, and rewritten into the bilayer by applying an appropriate bias on the conductive tip of an atomic force microscope. The lateral size and location of these polar nanodomains can be precisely controlled. Moreover, ring-shaped conductive domain walls are observed around these polar nanodomains, with on/off ratios of more than two orders of magnitude with respect to the ferroelectric background. Based on these characteristics, the polar nanodomains can be created, erased, and probed electrically, suggesting applications for high-density ferroelectric hard disks. [ABSTRACT FROM AUTHOR]

Abstract: During the course of tuning anisotropy from Ising type to zero, the variation of magnetization (M) steps against magnetic field (h) is investigated in a triangular antiferromagnetic Heisenberg model using Monte Carlo techniques. It is revealed that the anisotropy is an essential key to induce the temperature-dependent stepwise M(h) curve observed in frustrated magnetic system, and it can be employed to modulate this steplike magnetic behavior effectively. When the anisotropy is strengthened, a ground state transition occurs from the homogeneous 120° triangular structure to the collinear partially disordered antiferromagnetic state. No M step is detected in the system without anisotropy. But if the anisotropy is nonzero, the M 0/3 step (where M 0 is the saturated M) will emerge on M(h) curve, which is due to an h-induced quasi-collinear ferrimagnetic state. This M 0/3 step can be extended by increasing the anisotropy. When the M 0/3 plateau dominates the h-range broad enough, the equidistant metastable substeps, which originates from the disorders frozen in the frustrated collinear spin structure, appear to be superposed on the M 0/3 plateau. Thus the system with a strong anisotropy presents the whole temperature evolution of stepwise M(h) curve in quantitative agreement with the experiments of Ca3Co2O6. [Copyright &y& Elsevier]

Abstract: For the first time, a substorm event with double onsets is shown observationally under northward IMF condition in this study. Magnetic field data from ground stations and from geosynchronous satellite, and aurora data from IMAGE satellite are examined to study the substorm activity. The results show that the intensity and the spatial extent of the event are as large as those of typical substorms. Another interesting finding is that two expansion onsets seem to occur during the event. A possible mechanism for the two onsets was proposed. The energy source for the event was also discussed. [Copyright &y& Elsevier]

Exotic topological domains in BiFeO3 nanoislands have attracted much attention regarding their potential applications in advanced electronic devices. Here, different from the earlier reported disordered distributed BiFeO3 nanoislands formed by a self-assembly method, we fabricated an ordered BiFeO3 nanoisland array by mask-assisted pulsed laser deposition on a SrTiO3 substrate, which exhibits a center-converged in-plane polarization component and a monodomain pattern along the vertical direction. Such center-type quad-domain structures exhibit high stability, maintaining their topological structures after heating to 250 °C and subsequently cooling to room temperature. Moreover, they can be switched by applying a scanning electric field and recovered by applying a heating and cooling process. Observing this topological structure in BiFeO3 nanoislands might provide a suitable platform for further exploration of its topological phase transition properties, new functions, and potential applications. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

It is known that the utilization of exchange bias (EB) effect for data storage underscores its importance. However, achieving a giant EB effect with a small cooling field (HCF) in single-phase materials remains a challenge. This study unveils a giant EB value within a single-phase material, Fe2−xGaxTeO6 (FGTO), originating from the anchoring of spin-glass phase by antiferromagnetic order. Manipulating the relative strengths of the spin-glass and antiferromagnetic order parameters by Ga3+-substitution of Fe3+ ions in the Fe2TeO6 lattice governs the magnitude of the EB effect. It is found that FGTO single crystals synthesized via the chemical vapor transport do exhibit a remarkably large EB value as large as 1.5 T at x = 0.50 and a quite small cooling field HCF = 50 Oe. Investigations on the training effect, minor loop, and relaxation behavior unravel the intricate dynamics inherent to the spin-glass state. This study not only establishes a platform for exploring the EB effect in single-phase materials but also illuminates potential applications of FGTO in the realm of spintronics. [ABSTRACT FROM AUTHOR]

Hf0.5Zr0.5O2 (HZO) thin films are promising for applications in ferroelectric memories. However, these materials often face challenges, such as polarization fluctuations (e.g., fatigue and wake-up) and electric break-down incidents during the "1/0" write/read cycles, hindering their industrial application. Herein, fatigue, wake-up, and electric break-down seriously depend on both the electric field for polarization switching (Es) and the charge accumulation in the HZO film. More and more charges pin ferroelectric domains, and the sub-switching polarization introduces serious ferroelectric fatigue during the 1010 write/read cycles at Es ∼ 1.2Ec, where Ec is a ferroelectric coercive field. On the contrary, new charges increase rather slowly, and complete polarization switching is realized during the 1010 cycles at Es ∼ 1.5Ec, so the HZO film presents excellent polarization stability. A high Es ∼ 2Ec introduces the strong wake-up effect first; however, the serious charge accumulation largely increases leakage current and quickly introduces an electric break-down of the HZO film. Furthermore, it was found that the leakage current and dielectric permittivity can effectively monitor the charge accumulation and provide an early warning for fatigue and electric break-down. [ABSTRACT FROM AUTHOR]

We propose a new approach to obtain ultra-high piezoelectric coefficients that can be infinitely large theoretically, where ferroelectrics with strain-sensitive Curie temperature are necessary. We show the first-principles plus Monte Carlo simulation evidence that many hydrogen-bonded ferroelectrics (e.g. organic PhMDA) can be ideal candidates, which are also flexible and lead-free. Owing to the specific features of hydrogen bonding, their proton hopping barrier will drastically increase with prolonged proton transfer distance, while their hydrogen-bonded network can be easily compressed or stretched due to softness of hydrogen bonds. Their barriers as well as the Curie temperature can be approximately doubled upon a tensile strain as low as 2%. Their Curie temperature can be tuned exactly to room temperature by fixing a strain in one direction, and in another direction, an unprecedented ultra-high piezoelectric coefficient of 2058 pC/N can be obtained. This value is even underestimated and can be greatly enhanced when applying a smaller strain. Aside from sensors, they can also be utilized for converting either mechanical or thermal energies into electrical energies due to high pyroelectric coefficients. [ABSTRACT FROM AUTHOR]

The MAPbBr3 halide perovskite with a cubic paraelectric phase exhibits excellent semiconductor properties. Here, an interfacial polarization (Pin) at the ITO/MAPbBr3 Schottky junction can largely enhance photovoltaic current and be applied in the light and force multifunctional detector. An external force can alter the Pin and increase the photocurrent of the ITO/MAPbBr3/spiro‐OMeTAD/ITO detector, and a 1 N force increases the short‐circuit photocurrent by 120%. Furthermore, the ITO/MAPbBr3/ITO structure with one ITO surface in light and another ITO surface in dark exhibits an equivalent piezoelectric coefficient (d33) of up to 83 pC N−1 since the Pin and the corresponding photovoltaic current dynamically change with periodic external force. The light and force multifunctional detectors will promote the development and blend of optoelectronic devices and MEMS. [ABSTRACT FROM AUTHOR]

The anomalous transport phenomena and underlying mechanism of SrTiO3 have been long term concerned, including the Kondo physics and anomalous Hall effects to be discussed herein. Nevertheless, a clarification of the physical origins for these phenomena and their intertransitions upon varying carrier density remain to be an issue, due to the limited modulation of carrier density. Herein, the intriguing transport behaviors of electrolyte‐gated SrTiO3 in the field‐effect transistor geometry are investigated, which allows a relatively wide carrier density window. It is revealed that the remarkable Kondo‐like resistance upturn, identified at relatively low carrier density, becomes gradually disappeared and replaced by the emerging nonlinear Hall resistance with increasing gating voltage, indicating the interesting gating‐controlled transport behaviors. The detailed discussions on the underlying physics suggest that the gating‐controlled transport can be well described by the multiband transport model taking into account magnetic scattering in the channel layer, a comprehensive scenario for the emergent transport effects in carrier‐doped SrTiO3. The present work provides a promising platform for exploring novel quantum materials phenomena in SrTiO3 and analogous systems. [ABSTRACT FROM AUTHOR]

To understand the fascinating multiferroicity observed in CoCr2O4, Monte Carlo simulation is performed on a three-dimensional spinel lattice with classical Heisenberg spins. The conical spin order is confirmed to be the origin of the peculiar magnetoelectric behavior with coexisting magnetization and ferroelectric polarization. Furthermore, the simultaneous reversals of magnetization and polarization controlled by the external magnetic field are reproduced, consisting with the experimental observation qualitatively. It is revealed that, from the microscopic structures of spins, the axis of spin cone provides a “handle,” with which the magnetization and polarization can be reversed by the magnetic field easily. [ABSTRACT FROM AUTHOR]

The fantastic ferroelectric response to the magnetic field observed in Ca3CoMnO6 compound, where the ferroelectricity is driven by the collinear magnetism, is investigated by using Monte Carlo simulation based on a one-dimensional elastic Ising model. The microscopic domain structures of spins and ionic displacements are evaluated at different temperatures under different external magnetic fields. It is revealed that the up-up-down-down (↑↑↓↓) spin domains clamped with the domains of ionic displacement are responsible for the exotic ferroelectric behavior upon different magnetic fields in the low temperature range. [ABSTRACT FROM AUTHOR]

The fascinating magnetoelectric behavior as observed in Ca3CoMnO6 compound [Choi et al., Phys. Rev. Lett. 100, 047601 (2008)] is investigated by using Monte Carlo simulation based on a one-dimensional elastic Ising model. The macroscopic polarization results from the ionic displacements attributed to the exchange striction in an up-up-down-down (↑↑↓↓) spin ordering. In this scenario, the microscopic structures of spin and ionic displacement are investigated at different temperatures under different external electric fields to illuminate in detail the microscopic mechanism of the strong coupling between the magnetism and the ferroelectricity. It is revealed that the change in spin configuration dependent on temperature induces the freezing and melting phenomena of the polarized domains and thus the complicated temperature-dependent ferroelectric behavior in the whole low temperature range, namely the decline of the macroscopic polarization and the broad peak of dielectric constant. On the other hand, an external electric field also has influence on the magnetic structure through affecting the ionic displacements. [ABSTRACT FROM AUTHOR]

Single crystalline polar magnets (Mn1−xCox)2Mo3O8 (0 ≤ x ≤ 1) have been synthesized, and their magnetic properties have been studied. Magnetic interactions of the samples can be modulated drastically by Co-doping, and a ferrimagnetic to antiferromagnetic phase transition is identified at x = 0.35. For the samples hosting a ferrimagnetic state (0 ≤ x ≤ 0.3), square-like magnetic hysteresis loops are commonly identified, and the remnant magnetization and coercive field are revealed to strongly depend on the Co-content and temperature. The occupation ratio and magnetic nature of Co2+ are key ingredients to dictate the competition of various magnetic exchange couplings in the samples. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Monte Carlo simulations are employed to study the model of a triangular Ising antiferromagnet with the next-nearest neighbor ferromagnetic interaction (TIAFF), which can be well mapped to a six-state clock model, and provide a new model to explore the excitation of a topological six-state domain vortex. The TIAFF model retains the symmetry of the lattice and provides more details of vortex excitations and micro dynamics. The crossover of the domain walls in three sub-lattices creates the topological six-state domain vortices. The attractive force between the vortex and the anti-vortex is proportional to the number of domain walls that connect them. The movement of the vortex in the lattice is along the domain walls to avoid creating new defects. Our simulation works reveal that vortices obeying Arrhenius law are difficult to excite at a low temperature. Therefore, the surviving vortices are generated through the Kibble–Zurek mechanism (KZM), which explains the formation of topological solitons in a nonequilibrium system. The existing vortices in the system go through a slow random walk and annihilate in the first-order kinetic process. [ABSTRACT FROM AUTHOR]

In recent years, there is a surge of research interest in exotic ferroelectric topological states, motivated by their rich emerging physical properties and potential applications in nanoelectronic devices. Here, we demonstrate the observation of a sort of complex center-type topological domain structures, which exhibit a quadrant center-type (with polarization pointing to the center) topological texture for an in-plane polarization component and a cylinder domain pattern along the vertical direction, in rhombohedral structured Pb(Zr0.7Ti0.3)O3 (R-PZT) nanoislands. Such a center domain state exhibits a rather high stability, which can well maintain its topological texture after heating to above curie temperature and subsequently cooling down to room temperature. Moreover, it allows erasure by a scanning electric field, yet it can also be recovered by a similar heating and cooling process. The observation of these unique topological textures in R-PZT nanoislands might provide a good playground for further exploring their topological phase transition properties, emerging novel functionalities, and application potential. [ABSTRACT FROM AUTHOR]

In recent years, with the fast development of magnetic devices for information technology, the demands of magnetic thin films with both high functional stability and integration flexibility rapidly increase. It is believed that building a magnet with complementary advantages of van der Waals (vdW) and non-vdW magnets, which can be described as a "quasi-vdW magnet," will be highly appreciated. One may expect a quasi-vdW magnet to have chemical bonding between the neighboring sublayers for strong magnetic coupling, but to preserve clean surfaces with vdW feature for flexible interface engineering. For this purpose, an intercalation of magnetic atoms into the interlayer gaps of vdW magnets, as a powerful method for tuning the interlayer coupling, can be a practical approach. In this work, using the first-principles calculations, we study the potential to utilize the Fe-intercalation to transform the vdW magnets Fe3GeTe2 (FGT) into quasi-vdW magnets. As two extreme cases, it is revealed that: (i) the Fe-intercalated FGT bilayer Fe-[Fe3GeTe2]2 (Fe-[FGT]2) does have remarkable interlayer ferromagnetic coupling based on covalent bonding between the intercalated Fe atom and FGT monolayers and retains low exfoliation energy with vdW feature, suggesting that the Fe-[FGT]2 bilayer can be regarded as a quasi-vdW magnet; and (ii) the Fe-intercalation can transform the vdW FGT bulk into a non-vdW Fe-Fe3GeTe2 (Fe-FGT) bulk magnet. Accordingly, as for the intermediate cases, it is suggested that Fe-intercalated FGT multilayers (Fen−1-[FGT]n, n > 2) can also be potential quasi-vdW magnets, forming a family of magnetic thin films that provide alternative building blocks for microminiaturized magnetic devices. [ABSTRACT FROM AUTHOR]

Topological quad-domain textures in ferroelectric nanoislands have been considered as enablers for nanoelectric devices. However, the fabrication of ordered arrays of ferroelectric islands exhibiting this domain structure is a challenge. By using substrate patterning to create nucleation sites, highly ordered quad-domain ferroelectric polarization configurations were achieved in BiFeO3 nanoisland arrays. Reversible switching of the quad-domain between the center divergent state with highly conductive domain walls and the center convergent state with insulating domain walls can be realized, resulting in a resistance change with a large on/off ratio. This templated growth strategy enables the controllable fabrication of exotic topological domains and sheds light on their applications for configurable electronic devices. [ABSTRACT FROM AUTHOR]

Abstract: Nature offers structural solutions to various optimization problems. For example, an optimal, low‐shedding water transport at various scales is achieved with quasi‐fractal structures, shown to be close to optimal. In a series of projects, metallic network analogs of some of these solutions to make high‐efficiency transparent conductors are studied. Specifically, transparent conductors are developed by directly metalizing leaf venations, spider webs, and other organic fibers. Also, the natural process of self‐cracking, similar to that occurring in the mud of dried‐out riverbeds, is employed to develop masks for metallic network fabrications. These comprehensive studies and developments contributed to, and in some cases initiate new directions in the field of network transparent conductors. These structures offer performance exceeding those of conventional oxide‐based films, while providing a possibility of reduced processing expense. This paper provides a concise, comparative review of this study and other groups' efforts in recent years. In the context of applications, the performance criteria are defined, and with those as a guideline, practicality of the most promising networks is discussed. [ABSTRACT FROM AUTHOR]

Tin-based perovskite solar cells (TPSCs) have become a star candidate in lead-free perovskite cells due to their excellent optoelectronic properties and low toxicity. However, there are a lot of problems such as uncontrollable crystallizationprocess, easy oxidation of Sn2+ and high defect density have not been completely resolved in TPSCs. Here, the thiourea (TU) and ami-dine thiourea (ASU) are added into the perovskite precursor to regulate the microstructure, inhibit the oxidation of Sn2+ and promote charge transfer. The characterization results demonstrate that the TU additive can not only improve the micrograph, crystallinity and antioxidant, but also significantly induce recrystallization and passivate trap states. Thus, the TPSCs with TU (TU-modified TPSCs) show a significantly higher power conversion effi-cienc (PCE) and better stability than those of the TPSCs with ASU (ASU-mod-ified PSCs) and reference TPSCs. After stored in N2 atmosphere for 8 months, the unencapsulated TU-modified PSCs achieve a champion PCE of 10.9% with an open-circuit voltage of 0.79 V. Furthermore, the unsealed TU-modified PSCs can maintain 115% of its initial efficiency after stored in N2 atmosphere for one year. This is the longest lifetime of unencapsulated pure TPSCs in N2 atmosphere. [ABSTRACT FROM AUTHOR]

Nowadays many semantic segmentation algorithms have achieved satisfactory accuracy on von Neumann platforms (e.g., GPU), but the speed and energy consumption have not meet the high requirements of certain edge applications like autonomous driving. To tackle this issue, it is of necessity to design an efficient lightweight semantic segmentation algorithm and then implement it on emerging hardware platforms with high speed and energy efficiency. Here, we first propose an extremely factorized network (EFNet) which can learn multi-scale context information while preserving rich spatial information with reduced model complexity. Experimental results on the Cityscapes dataset show that EFNet achieves an accuracy of 68.0% mean intersection over union (mIoU) with only 0.18M parameters, at a speed of 99 frames per second (FPS) on a single RTX 3090 GPU. Then, to further improve the speed and energy efficiency, we design a memristor-based computing-in-memory (CIM) accelerator for the hardware implementation of EFNet. It is shown by the simulation in DNN+NeuroSim V2.0 that the memristor-based CIM accelerator is ∼ 63 × (∼ 4.6 ×) smaller in area, at most ∼ 9.2 × (∼ 1000 ×) faster, and ∼ 470 × (∼ 2400 ×) more energy-efficient than the RTX 3090 GPU (the Jetson Nano embedded development board), although its accuracy slightly decreases by 1.7% mIoU. Therefore, the memristor-based CIM accelerator has great potential to be deployed at the edge to implement lightweight semantic segmentation models like EFNet. This study showcases an algorithm-hardware co-design to realize real-time and low-power semantic segmentation at the edge. • An efficient lightweight semantic segmentation model named EFNet is designed. • EFNet achieves 68.0% mIoU and 99 FPS on the Cityscapes dataset with only 0.18 M parameters. • Implementing EFNet on a memristor-based CIM accelerator realizes high speed and energy efficiency. [ABSTRACT FROM AUTHOR]

The ferroelectric polarization and phase diagram in Tm-doped GdMnO3 are studied by means of Monte Carlo simulation based on the Mochizuki–Furukawa model. Our work well reproduces the low temperature polarization at various substitution levels observed experimentally. It is demonstrated that the Tm-doping can control the multiferroic behaviors through modulating the spin structures, resulting in the flop of the electric polarization. In addition, the polarization in the ab-plane cycloidal spin phase arises from comparable contributions of the symmetric exchange striction and antisymmetric exchange striction, leading to much bigger polarization than that in the bc-plane cycloidal spin phase where only the contribution of the latter striction is available. The phase diagram obtained in our simulation is helpful for clarifying the multiferroic properties in doped manganite systems and other related multiferroics. [ABSTRACT FROM AUTHOR]

Deterministically controllable multi‐state polarizations in ferroelectric materials are promising for the application of next‐generation non‐volatile multi‐state memory devices. However, the achievement of multi‐state polarizations has been inhibited by the challenge of selective control of switching pathways. Herein, an approach to selectively control 71° ferroelastic and 180° ferroelectric switching paths by combining the out‐of‐plane electric field and in‐plane trailing field in multiferroic BiFeO3 thin films with periodically ordered 71° domain wall is reported. Four‐state polarization states can be deterministically achieved and reversibly controlled through precisely selecting different switching paths. These studies reveal the ability to obtain multiple polarization states for the realization of multi‐state memories and magnetoelectric coupling‐based devices. [ABSTRACT FROM AUTHOR]

In recent years, one of the urgent issues for two dimensional (2D) magnetic materials is to find efficient ways in enhancing the magnetic ordering temperature Tc. It is believed that an in-plane (IP) compressive strain can greatly enhance the interatomic interactions by shortening the chemical bond length if at all possible, leading to the enlarged spin exchange and possibly higher Tc. However, a large compressive strain usually favors antiferromagnetic (AFM) ordering due to growing dominance of the Pauli exclusion principle, in contradiction with the common requirement of nonzero magnetization. In compromise, ferrimagnetic (FiM) ordering can be alternated by synthesizing artificial 2D compound with two magnetic sublattices. In this work, we propose a V-implanted CrI3 monolayer, short for V-(CrI3)2, and study its FiM ordering under a series of IP biaxial strains using the first-principles calculations and Monte Carlo simulations. It is found that the V-(CrI3)2 monolayer may evolve from the stripy-type AFM insulator toward the FiM half-metal with net magnetic moment of 5.0 μB/f.u. aligned in parallel to the ab-plane upon increasing the IP biaxial strain up to ∼−3% (compressive strain) and beyond. As the IP biaxial strain increases up to ∼−5%, the Tc of the FiM state may be raised to room temperature. This work suggests that the IP strain engineering combined with spin implantation can be an alternative strategy for enhancing 2D magnetism. [ABSTRACT FROM AUTHOR]

Optical second harmonic generation (SHG) is a sensitive and powerful technique to probe various symmetry breaking, especially ferroelectric/magnetic domains, in artificial thin films or heterostructures. In a wide range of ferroelectric crystals, a non‐trivial broken symmetry will emerge at domain boundaries, however, the contribution of such symmetry breaking to SHG is often neglected due to its random orientation. Here, a co‐polarized SHG effect from the well‐aligned domain wall arrays is observed in BiFeO3 thin films. This SHG component is highly dependent on the local orientation of the wall arrays, and its polarization feature reveals the Néel‐like evolution of electric polar vectors in the wall region. Based on this intriguing effect, mixed‐phase patches with four possible orientations in the quasi‐tetragonal stripes are identified by polarization‐sensitive SHG mapping. These findings not only clarify a critical SHG contribution in this multiferroic material, but also demonstrate an optical approach for exploring phase‐determined function unit. [ABSTRACT FROM AUTHOR]

Review: [99 refs.] [ABSTRACT FROM AUTHOR]

So far tens of multiferroic materials, with various chemical compositions and crystal structures, have been discovered in the past years. Among these multiferroics, some perovskite manganites with ferroelectricity driven by magnetic orders are of particular interest. In these multiferroic perovskite manganites, the multiferroic phenomena are not only quite prominent, but the involved physical mechanisms are also very plenty and representative. In this brief review, we will introduce some recent theoretical and experimental progress on multiferroic manganites, including the fascinating microscopic physics and very recently addressed experimental findings with attractive multiferroicity. [ABSTRACT FROM AUTHOR]

MAPbI3, MAPbBr3, and CsPbBr3 are excellent halide perovskite semiconductors with super long carrier diffusion length, long minority carrier lifetime, and large light absorption coefficient. Compared with the small intrinsic electrostriction, photocarriers induce a large photostriction in the surface layer. Furthermore, an electric field can efficiently separate the light excited electron–hole pairs, enhance photocarriers diffusion, and finally increase the crystal expansion, i.e., photo-electro-striction. For each crystal under 30 V/mm and in light with 450 nm wavelength and 840 mW/cm2, the photo-electro-striction is over four times of the pure electrostriction and is larger than the sum of photostriction and electrostriction. Most importantly, MAPbI3 single crystal shows a large photostriction of ∼0.35% and the photo-electro-striction of ∼0.64%. This work proves a very large photo-electro-striction as a result of the strong coupling among photocarriers, electric fields, and crystal lattices, which is important to develop semiconductor devices. [ABSTRACT FROM AUTHOR]

• The backpropagation with gradient accumulation (BP-GA) algorithm is proposed. • The BP-GA algorithm can tolerate significant memristor non-idealities. • The BP-GA algorithm is insensitive to learning rate. • The robustness of the BP-GA algorithm is attributed to the gradient accumulation. Memristive neural network (MNN) has emerged as a new computing architecture with high speed and low power consumption, but its hardware implementation is hampered mainly by the device non-idealities of memristors. Here, we propose a backpropagation with gradient accumulation (BP-GA) algorithm which can effectively tolerate the memristor non-idealities. We first show that a memristor-based single-layer perceptron trained with BP-GA achieves high image recognition accuracies (>85% on the MNIST dataset) with a wide range of learning rates (0.01–50), large nonlinearities (>6), a small number of conductance states (even down to 3 states), a broad spectrum of ON/OFF ratios (across 3 orders of magnitude), and large noises (up to 40%). The origin for such good robustness against the learning rate and memristor non-idealities is then investigated and revealed to be associated with the operation mechanism of BP-GA. In this algorithm, the weights can keep increasing in magnitude due to the gradient accumulation and therefore become movable even at a small learning rate (or a large ON/OFF ratio equivalently). Moreover, the weights corresponding to the foreground and background of the input image are appropriately moved to the positive and negative boundaries of the weight range, respectively, thus allowing the learning of the image features using only a small number of conductance states. These boundary weights are trapped there without significant oscillation under the effects of accumulated gradients, resulting in immunity to large nonlinearity and noise. Therefore, BP-GA enables the MNN to be insensitive to the learning rate and robust against the memristor non-idealities. The performance of BP-GA is further evaluated on the memristor-based multilayer perceptron (on the MNIST dataset) and convolutional neural network (on the Cifar-10 dataset). For both MNNs, BP-GA exhibits relatively high accuracies and good tolerance against memristor non-idealities, demonstrating its applicability to complex networks and problems. This study provides a viable approach at the algorithm level for addressing some important hardware implementation issues of MNNs using realistic memristors. [ABSTRACT FROM AUTHOR]

Hydrogels have emerged as promising materials for the construction of skin-like mechanical sensors. The common design of hydrogel-based artificial skin requires a dielectric sandwiched between two hydrogel layers for capacitive sensing. However, such a planar configuration limits the sensitivity, stretchability and self-healing properties. Here, we report the design of single-layer composite hydrogels with bulk capacitive junctions as mechanical sensors. We engineer dielectric peptide-coated graphene (PCG) to serve as homogenously dispersed electric double layers in hydrogels. Any mechanical motions that alter the microscopic distributions of PCG in the hydrogels can significantly change the overall capacitance. We use peptide self-assembly to render strong yet dynamic interfacial interactions between the hydrogel network and graphene. The resulting hydrogels can be stretched up to 77 times their original length and self-heal in a few minutes. The devices can effectively sense strain and pressure in both air and aqueous environments, providing tremendous opportunities for next-generation iontronics. [ABSTRACT FROM AUTHOR]

Polymer-based dielectrics exhibit promising applications in energy storage devices due to their enormous power density, good flexibility, and low cost. However, the low energy storage density remains to be the bottleneck. Here, sandwiched polymer-ceramic nanocomposite films are designed by stacking the PVDF middle layer incorporated Ag-decorated BaTiO 3 (BT) ceramic nanoparticles (Ag@BT NPs) and the PVDF top/bottom layers embedded 2D layered MXene nanosheets. Interestingly, the optimal performances with a reversible energy storage density (W re) as high as ∼ 22.3 J/cm3 with an efficiency η ∼ 77% at a low electric field of 270 MV/m are achieved for the film with 5 wt% DA@Ag@BT/PVDF middle layer. Strong interfacial coupling, ionic interaction, and enhanced breakdown strength due to the Coulomb blocking effect in the hierarchical structures with different fillers are responsible for the high energy storage performance. Moreover, the phase-field simulation further proved an appropriate amount of DA@Ag@BT NPs can effectively prevent the formation of the conductive network, inhibit the dielectric loss and improve the breakdown strength. This hierarchical strategy demonstrates an applicable route for fabricating polymer nanocomposites with high performance. [ABSTRACT FROM AUTHOR]

The built-in electric field existing in heterojunction of hybrid photocatalyst is favorable to separate the photogenerated carriers in photocatalytic reaction. Besides, the electric field existing in the whole ferroelectric bulk can also effectively separate the photogenerated carriers. Here the catalytic reaction is enhanced through the enlarged electric field contributed by both p-n junction and the ferroelectric polarization. A new composite is prepared with the n-type single-crystal PbTiO 3 nanoplate coated with the p-type NiO particles, and its photocatalytic degradation rate of RhB (0.253 min−1) is 4.71 times of pure PbTiO 3 (0.0537 min−1) due to the contribution of p-n junction. In addition, the piezo-phototronic effect is applied to further enhance the photocatalytic performance. Under light and ultrasonic excitation, the screening effect of ferroelectric polarization can be broken by the alternating piezoelectric potential due to the periodic mechanical stress, and thus the reaction rate of piezo-photocatalytic degradation of RhB (0.461 min−1) is 1.82 times of photocatalytic reaction rate (0.253 min−1) for NiO@PbTiO 3 composite and 3.34 times of the piezo-photocatalytic reaction rate for pure PbTiO 3 (0.138 min−1). This work is helpful to clarify the piezo-photocatalytic mechanism and develop efficient photocatalysts. [ABSTRACT FROM AUTHOR]

Abstract: Based on the fact that the transcription of STAT-1 plus its Serine 727 and Tyrosine 701 phosphorylation is not the pre-requisite for the cell death signal transduction in the IFN-γ signaling pathway induced by co-immobilized IFN-γ/TNF-α, we investigate both in vitro and in vivo the key transcription regulators to promote the signal transduction of HeLa cells. It is found that IFN-γ R2 is the important death signal receptor in the HeLa cell death by RNA interference. Checking the expression of the whole transcription (STAT) protein family reveals that STAT-6 is highly expressed in comparison with the other STAT proteins. The gene silence of IFN-γ R2 leads to the down-regulation of STAT-6 and phosphorylation-STAT-6 (p-STAT-6) expressions. The successful gene silence of STAT-6 results in the reduction of HeLa cell programmed death and the expression of several important key factors related to programmed cell death (p53, Bcl-2, and Bax). More importantly, our in vivo experiments by injecting nanoparticle drug carriers with the co-immobilized IFN-γ/TNF-α into nude mice model confirm the high expression of STAT-6 and p-STAT-6. It is thus concluded that, in response to IFN-γ, the co-immobilized IFN-γ/TNF-α unusually promotes the activation of STAT-6 rather than STAT-1, resulting in the enhanced cell programmed death in HeLa. The present work reveals the gene-level molecular mechanism of IFN-γ/TNF-α co-immobilized on biomaterials as a potentially effective therapy against cancer cells. [Copyright &y& Elsevier]

Two-dimensional (2D) van der Waals (vdW) ferromagnetic (FM) materials have recently received attention due to their potential applications in next-generation spintronic devices. However, the reduced dimensionality and weak interlayer vdW interaction seriously suppress the magnetic Curie temperature Tc, raising the concern with enhancing the interlayer FM coupling. It is argued that proper ion intercalation may enhance the interlayer coupling by establishing strong chemical bonding. In this work, this issue in a 2D vdW FM Fe3GeTe2 (FGT) bilayer as an example is addressed, and our first-principles calculations predict that beryllium (Be) can be a promising intercalant for such enhancement. It is revealed that the Be-ion migration in-between the vdW gap has only moderate energy barriers owing to its small ionic radius, suggesting the feasibility of reversible intercalation. Particularly, Be-ion intercalation can significantly enhance the interlayer FM coupling by reducing the interlayer distance. The strong bonding that pulls two FGT monolayers closer is ascribed to orbital hybridization between Be-ions and interfacial Te-FeI sites. Be-ion intercalation also contributes to electron doping via charge transfer, favoring the enhanced intralayer FM coupling. This work suggests an alternative scheme for reversibly controlled ferromagnetism enhancement in 2D vdW ferromagnets using ion intercalation. [ABSTRACT FROM AUTHOR]

CsPbBr3 shows excellent photoelectric properties such as a direct bandgap of 2.25 eV, large optical absorption coefficient, and strong luminescence intensity. Therefore, it is promising to be applied in LED devices. It is important to modulate and enhance photoluminescence (PL) intensity through external stimulus. Here, (001) CsPbBr3 films with nanocrystals were grown on the PMN-PT ferroelectric single crystal substrate, and its PL can be largely modulated by the ferroelectric polarization switching of PMN-PT. The saturated polarization of a 90 nm thick CsPbBr3 film induces a 67% increase in the PL intensity, which is due to piezoelectric strain passivated defects, resulting in decreased nonradiative recombination. However, the upward saturated polarization of the 40 nm thick CsPbBr3 film introduces a 55% decrease in the PL intensity, which can be attributed to the inner electric field separating the light-excited electron–hole pairs, thereby decreasing their radiative combination. This reversible and tunable photoluminescence is important for the development of advanced multifunctional optoelectrical devices. [ABSTRACT FROM AUTHOR]