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Electrons have not only charge and spin degrees of freedom, but also additional valley degrees of freedom. The search for valleytronic materials with large valley splits is important for the development of valleytronics. In this work, we applied first principles computations to calculate 1 L Hf3C2O2 at the level of HSE06. When the spin–orbit coupling (SOC) effect is considered, 1 L Hf3C2O2 is an indirect bandgap semiconductor with a bandgap of 0.952 eV. Meanwhile, valley splitting occurs between the conduction bands Γ and K, with a valley splitting value as high as 98.228 meV. Bader charge analysis was used to determine that Hf–O and Hf–C are ionic bonds. The computed elastic constants and phonon spectra proved that 1 L Hf3C2O2 is mechanically and dynamically stable. In addition, the Berry curvature of 1 L Hf3C2O2 is non-zero. In the work the effect of the electronic properties of 1 L Hf3C2O2 was also calculated with respect to the biaxial strain. The results show that the biaxial strain can well regulate the band gap and valley splitting. Finally, we calculated the effects of hole and electron doping on the band gap and valley splitting of 1 L Hf3C2O2. The results show that the band gap and valley splitting are linearly related to the doping concentration. Our study shows that 1 L Hf3C2O2 is a promising two-dimensional valleytronics material. [ABSTRACT FROM AUTHOR]

The aim of voltage control of magnetism is to reduce the power consumption of spintronic devices. For a spin valve, the relative magnetic orientation for the two ferromagnetic layers is a key factor determining the giant magnetoresistance (GMR) ratio. However, achieving full voltage manipulation of the magnetization directions between parallel and antiparallel states is a significant challenge. Here, we demonstrate that by utilizing two exchange-biased Co/IrMn bilayers with opposite pinning directions and with ferromagnetic interlayer coupling between the two Co layers, the magnetization alignment of the two Co layers of a spin valve can be switched between antiparallel and nearly parallel states by voltage-induced strain, leading to a full voltage control of GMR in a repeatable manner. The magnetization rotating processes for the two Co layers under different voltages can be clearly demonstrated by simulations based on the Landau–Lifshitz–Gilbert equation. This work provides valuable references for the development of full voltage-controlled spintronic devices with low energy consumption. [ABSTRACT FROM AUTHOR]

Non-destructive testing (NDT) enables the determination of internal defects and flaws in concrete structures without damaging them, making it a common application in current bridge concrete inspections. However, due to the complexity of the internal structure of this type of concrete, limitations regarding measurement point placement, and the extensive detection area, accurate defect detection cannot be guaranteed. This paper proposes a method that combines the Simultaneous Algebraic Reconstruction Technique with Group Sparsity Regularization (SART-GSR) to achieve tomographic imaging of bridge concrete under sparse measurement conditions. Firstly, a mathematical model is established based on the principles of the tomographic imaging of bridge concrete; secondly, the SART algorithm is used to solve for its velocity values; thirdly, on the basis of the SART results, GSR is applied for optimized solution processing; finally, simulation experiments are conducted to verify the reconstruction effects of the SART-GSR algorithm compared with those of the SART and ART algorithms. The results show that the SART-GSR algorithm reduced the relative error to 1.5% and the root mean square error to 89.76 m/s compared to the SART and ART algorithms. This improvement in accuracy makes it valuable for the tomographic imaging of bridge concrete and provides a reference for defect detection in bridge concrete. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) ferroelectrics has emerged as a promising building block for nonvolatile memory devices. In this work, we demonstrate the out-of-plane ferroelectricity of 2D CuCrP2S6 (CCPS) at the room temperature and the switchable diode effect in 2D CCPS-based ferroelectric nanodevices. The spontaneous out-of-plane ferroelectric polarization switching and hysteresis loops are directly evidenced by the piezoresponse force microscopy. The intrinsic ferroelectricity originates from the non-centrosymmetric structure of 2D CCPS, which is confirmed by optical second-harmonic generation technique. A ferroelectric tunnel junction was built up by using 2D CCPS as a function layer. The observed diode-like forward rectification effect of CCPS diode is opposite to the direction of remnant polarization, which is attributed to the ferroelectric polarization modulation of Schottky barrier. Our work highlights the great potential of 2D CCPS in ultrathin ferroelectric memory device and motivates the development of multifunctional nanodevices. [ABSTRACT FROM AUTHOR]

Spin–orbit torque provides an efficient way to achieve switching of perpendicular magnetization, which is essential for designing energy-efficient spintronic devices. An in-plane antidamping torque combined with an out-of-plane antidamping torque can often deterministically switch perpendicular magnetization without an external magnetic field. Encouragingly, field-free perpendicular magnetization switching of a two-dimensional (2D) material WTe2/ferromagnet bilayer has been reported recently, but the working temperature (< 200 K) is quite below room temperature. Here, we demonstrate field-free perpendicular magnetization switching in the Pt/Co/Pt/WTe2 multilayer films at room temperature, which is mainly attributed to the out-of-plane antidamping torque originating from the WTe2 layer. In addition, current-induced perpendicular magnetization switching at zero magnetic field is also accomplished in the [Co/Pt]2/WTe2 multilayer film with a very large perpendicular magnetic anisotropic field (∼13 600 Oe), which is very useful for practical applications. This work offers a potential way to develop spintronic devices based on 2D materials at room temperature. [ABSTRACT FROM AUTHOR]

Two-dimensional van der Waals ferroelectrics with in-plane polarization are less vulnerable to the depolarization field effect, making them practically more favorable in device applications. Herein, symmetric planar memristor based on two-dimensional van der Waals WO2Cl2 was fabricated and electrically characterized, showing significant memory effect with a current ON/OFF ratio up to 104 and stable switching cycles. Both short-term plasticity and long-term potentiation were observed in synaptic simulations by applying consecutive positive and negative pulses, respectively, which demonstrates the potential capability of this WO2Cl2 memristor in neuro-morphic computing as an artificial synapse. [ABSTRACT FROM AUTHOR]

As a promising van der Waals (vdW) magnet, Fe3GeTe2 (FGT) has an inversion symmetry in structure, thus nominally prohibiting the generation of the Dzyaloshinskii–Moriya interaction and the resultant topological Hall effect (THE), which is manifested as hump-like features in transport. By virtue of doping, like the method of fabricating heterostructures, the crystal inversion symmetry of FGT could be broken artificially; therefore, humps of Hall resistance due to the THE are expected. However, alternative interpretations indicate inhomogeneity-induced multi-channel anomalous Hall effect (AHE) could also give rise to these humps. Here, besides the magnetic properties modified by Co doping, we report emergent humps in (Fe0.74Co0.26)3GeTe2 (FCGT) nanodevices. By scanning minor loops, partial anomalous Hall loops exceeding the full loop cannot be attributed to the THE, while it is in line with the multi-channel AHE scenario. These channels likely develop as a result of the Co atoms in FGT being randomly distributed, leading to multiple spatially separated magnetic regions with distinct coercive fields and magnetizations. By combing these AHE channels, the hump features in FCGT are effectively reproduced. Our work implies that the underlying multi-channel transport could also facilitate the development of versatile nanodevices utilizing the doped vdW ferromagnets. [ABSTRACT FROM AUTHOR]

The fluctuation of switching parameters is unavoidable in conductive filaments (CFs)-type resistive switching (RS) devices, which restricts the application in resistive random-access memory. Here, we employed an uninsulated antiferromagnetic (AFM) NiO layer adhered to a well-insulating HfO2 layer to effectively suppress the RS fluctuation by achieving forming-free, narrower set voltage distribution, a more stable on/off ratio, and better endurance in comparison with single-HfO2-layer based RS devices. The conduction scaling behavior indicates that the NiO/HfO2 bilayer has a smaller scale parameter S0 (lateral dimension of the bottleneck for the CFs). Besides this, considering some preexisting conductive paths in the NiO layer, the electric fields and the formation/rupture of CFs can be highly localized, leading to reduced switching fluctuation and improved RS performance in the NiO/HfO2-based RS devices. Moreover, asymmetric I–V curves measured in a high resistance state (HRS) in positively and negatively biased regions and the electric modulation of exchange bias (EB) arising from the Co-NiO interfacial coupling are favorable for revealing the inherent mechanism for RS. The coexistence of RS and EB is also useful to the design of novel multifunctional memory devices. [ABSTRACT FROM AUTHOR]

Manipulation of exchange bias (EB) via spin-current-induced spin–orbit torque (SOT) is of great importance in developing full electric control spintronic devices. Here, we report on SOT-dominant manipulation of the interfacial antiferromagnetic spins and the related perpendicular EB (PEB) in the IrMn/Co1-xTbx (CoTb) bilayers with various Tb contents. No matter the magnetization of the ferrimagnetic CoTb layer is Co-dominant or Tb-dominant; all the samples were perpendicularly magnetized, and spontaneous PEB could be established during the isothermal crystallization of the IrMn layer. The SOT-induced EB switching could be accomplished with assistance of an in-plane or out-of-plane external magnetic field, associated with a monotonic reduction of the EB switching fraction by increasing x. This phenomenon is attributed to weakening of the interfacial exchange coupling between the CoTb and IrMn layers as x is increased. These findings provide a way to design high energy-efficient spintronic devices by employing the antiferromagnet/ferrimagnet bilayers, which may have weak stray field and strong robustness in contrast to commonly used heavy-metal/ferromagnet/antiferromagnet trilayers. [ABSTRACT FROM AUTHOR]

Resistance random access memories (RRAM) show excellent potential applications for nonvolatile data storage. Recently, one of the most representative materials is the MoS2–xOx fabricated by oxidation of the MoS2 flake. The resistive switching (RS) effect was observed in the graphene/MoS2–xOx/graphene device. This bulk-type RS device has a low Roff/Ron ratio. In addition, interface-type RS effect can be more attractive, which is not explored in MoS2–xOx devices yet. In this work, a bipolar interface-type RS effect is observed in Au/MoS2–xOx (MSO)/Au device for the first time. By inserting the Ti layer between top Au and MSO layers, a high stable bipolar interface-type RS effect is observed, and the Roff/Ron ratio is significantly increased by two orders of magnitude. The performance improvement can be understood by the redox reaction of the interface Ti/MSO. This work could provide a reference for improving the performance of RS devices. [ABSTRACT FROM AUTHOR]

Transition‐metal oxide (TMO) heterostructures provide fertile grounds for creating and manipulating intriguing properties and functionalities. At the interface of TMO heterostructures, electronic reconstructions generally occur via charge transfer and lead to an extraordinary spectrum of emergent phenomena but unattainable in their bulk constituents. However, the basic mechanism of charge transfer at the interface is not fully determined or even understood in heterostructures, which may hide the underlying mechanisms and intriguing physics. Herein, an intrinsic charge transfer and resultant exotic ferromagnetism are unambiguously observed in the heterostructures between the nonmagnetic LaCoO3 (LCO) and SrTiO3 (STO). Combining element‐specific X‐ray absorption spectroscopy and atomic multiplet fitting, direct evidence of charge transfer‐induced multivalence of cobalt ions, interactions of which would contribute to the novel magnetism beyond the intuition, in concert with first‐principles density‐functional‐theory calculations, is demonstrated. Beyond LCO/STO system, a more broadly applicable principle for the heterostructures between 3d TMO and STO where charge transfer and resultant multivalence or conducting interfaces are coexistent is establish. This study represents an advance that the electronic reconstruction and the multiple electron configurations of 3d transition metal ions will constitute a powerful tool for the designs of functional materials and creations of unconventional physical properties. [ABSTRACT FROM AUTHOR]

Controlled doping of transition‐metal dichalcogenide (TMDC)‐layered materials is of great importance for practical device application. Doping of TMDCs and tuning of the bandgap properties remain challenging owing to the difficulty of breaking covalent bonds. In this work, the doping of V, Fe, and Nb atoms into MoSe2 is successfully synthesized using the chemical vapor transport method. By the absorption of V or Nb dopants, the intrinsic n‐type MoSe2 is tuned to be of p type. A p‐n diode based on a homojunction is fabricated by stacking the n‐ and p‐type MoSe2 vertically. The photoresponse range of intrinsic MoSe2 is only up to 785 nm. However, the photodetector based on the doped MoSe2 flake with V, Fe, and Nb can be used up to the near‐infrared (1550 nm) region at room temperature. Furthermore, the photoresponse wavelength of a V‐doped MoSe2 could reach up to 10 µm. The results indicate that the elemental doping methods could enrich the electrical and optical application prospects of MoSe2. [ABSTRACT FROM AUTHOR]