Rare-Earth Permanent Magnet SmCo5 for Chiral Interfacial Spin-Orbitronics

Interfacially asymmetric magnetic multilayers made of heavy metal/ferromagnet have attracted considerable attention in the spintronics community for accommodating spin-orbit torques (SOTs) and meanwhile for hosting chiral spin textures. In these multilayers, the accompanied interfacial Dzyaloshinskii–Moriya interaction (iDMI) permits the formation of Néel-type spin textures. While significant progresses have been made in Co, CoFeB, Co₂FeAl, CoFeGd based multilayers, it would be intriguing to identify new magnetic multilayers that could enable spin-torque controllability and meanwhile host nanoscale skyrmions. In this report, first, thin films made of permanent magnet SmCo₅ with perpendicular magnetic anisotropy are synthesized, in which the deterministic SOT switching, enabled by the spin Hall effect, in Pt/SmCo₅/Ta trilayer is demonstrated. Further, the stabilization of room-temperature skyrmions with diameters ≈100 nm in [Pt/SmCo₅/Ta]₁₅, together with a skyrmionium-like spin texture in [Pt/SmCo₅/Ir]₁₅ multilayers is shown. Based on the material specific parameters, micromagnetic simulations are also carried out. The results confirm the presence of chiral spin textures in this new material family. Through interfacial engineering, the results thus demonstrate that rare earth permanent magnets could be a new platform for studying interfacial chiral spintronics.     

Strain-Controlled Spin Wave Excitation and Gilbert Damping in Flexible Co2FeSi Films Activated by Femtosecond Laser Pulse

The dynamic response of magnetic order to optical excitation at sub-picosecond scale has offered an intriguing alternative for magnetism manipulation. Such ultrafast optical manipulation of magnetism has become a fundamental challenging topic with high implications for future spintronics. Here, this study demonstrates such manipulation in Co₂FeSi films grown on flexible polyimide substrate, and demonstrates how the magneto-optical interaction can be modified by using strain engineering which in turn triggers the excitation of both dipolar and exchange spin waves modes. Furthermore, Gilbert damping and spin-orbit coupling in Co₂FeSi can both be tuned significantly by altering the magnitude and type of applied strain, suggesting an appealing way to manipulate spin wave propagation. These results develop the optical manipulation magnetism into the field of spin wave dynamics, and open a new direction in the application of spin orbitronics and magnonics devices using strain engineering.     

Anomalous Anisotropic Magnetoresistance of Antiferromagnetic Epitaxial Bimetallic Films: Mn2Au and Mn2Au/Fe Bilayers

Recently intensive efforts have been devoted to the emerging field of antiferromagnetic (AFM) spintronics, where ferromagnetic electrodes are substituted by antiferromagnets. This study investigates the anisotropic magnetoresistance (AMR) of epitaxial tetragonal antiferromagnetic bimetallic films: Mn₂Au and Mn₂Au/Fe bilayers. An anomalous AMR effect with additional peaks is observed. This study theoretically and experimentally demonstrates that the AFM spins of Mn₂Au can be viewed and controlled at room temperature, and this is achievable with a notably relatively small magnetic field of 200 mT. Strong hybridization between Au and Mn, and strong modification of the intrinsic quadratic anisotropy of Mn₂Au from interfacial biquadratic anisotropy result in an additional anomalous AMR component of 1%. The findings suggest that Mn₂Au films can be used in room temperature antiferromagnetic spintronics.     

Multifunctional Lateral Transition‐Metal Disulfides Heterojunctions

The intrinsic spin‐dependent transport properties of two types of lateral VS₂|MoS₂ heterojunctions are systematically investigated using first‐principles calculations, and their various nanodevices with novel properties are designed. The lateral VS₂|MoS₂ heterojunction diodes show a perfect rectifying effect and are promising for the applications of Schottky diodes. A large spin‐polarization ratio is observed for the A‐type device and pure spin‐mediated current is then realized. The gate voltage significantly tunes the current and rectification ratio of their field‐effect transistors. In addition, they all demonstrate a sensitive photoresponse to blue light, and could be used as photodetector and photovoltaic device. Moreover, they generate an effective thermally driven current when a temperature gratitude appears between the two terminals, suggesting them as potential thermoelectric materials. Hence, the lateral VS₂|MoS₂ heterojunctions show a multifunctional nature and have various potential applications in spintronics, optoelectronics, and spin caloritronics.     

Graphene Oxide Quantum Dots Based Memristors with Progressive Conduction Tuning for Artificial Synaptic Learning

Memristors as electronic artificial synapses have attracted increasing attention in neuromorphic computing. Emulation of both “learning” and “forgetting” processes requires a bidirectional progressive adjustment of memristor conductance, which is a challenge for cutting‐edge artificial intelligence. In this work, a memristor device with a structure of Ag/Zr_0.5Hf_0.5O₂:graphene oxide quantum dots/Ag is presented with the feature of bidirectional progressive conductance tuning. The conductance of proposed memristor is adjusted through voltage pulse number, amplitude, and width. A series of voltage pulses with an amplitude of 0.6 V and a width of 30 ns is enough to modulate conductance. The impacts of pulses with different parameters on conductance modulation are investigated, and the potential relationship between pulse amplitude and energy is revealed. Furthermore, it is proved that the pulse with low energy can realize the almost linear conductance regulation, which is beneficial to improve the accuracy of pattern recognition. The bidirectional progressive conduction modulation mimics various plastic synapses, such as spike‐timing‐dependent plasticity and paired‐pulse facilitation. This progressive conduction tuning mechanism might be attributed to the coexistence of tunneling effect and extrinsic electrochemical metallization effect. This work provides one way for memristor to attain attractive features such as bidirectional tuning, low‐power consumption, and fast speed switching that is in urgent demand for further evolution of neuromorphic chips.     

A Leaky‐Integrate‐and‐Fire Neuron Analog Realized with a Mott Insulator

During the last half century, the tremendous development of computers based on von Neumann architecture has led to the revolution of the information technology. However, von Neumann computers are outperformed by the mammal brain in numerous data‐processing applications such as pattern recognition and data mining. Neuromorphic engineering aims to mimic brain‐like behavior through the implementation of artificial neural networks based on the combination of a large number of artificial neurons massively interconnected by an even larger number of artificial synapses. In order to effectively implement artificial neural networks directly in hardware, it is mandatory to develop artificial neurons and synapses. A promising advance has been made in recent years with the introduction of the components called memristors that might implement synaptic functions. In contrast, the advances in artificial neurons have consisted in the implementation of silicon‐based circuits. However, so far, a single‐component artificial neuron that will bring an improvement comparable to what memristors have brought to synapses is still missing. Here, a simple two‐terminal device is introduced, which can implement the basic functions leaky integrate and fire of spiking neurons. Remarkably, it has been found that it is realized by the behavior of strongly correlated narrow‐gap Mott insulators subject to electric pulsing.     

Artificial Synapse Based on Oxygen Vacancy Migration in Ferroelectric-Like C-Axis-Aligned Crystalline InGaSnO Semiconductor Thin-Film Transistors for Highly Integrated Neuromorphic Electronics

Artificial synapses are a key component of neuromorphic computing systems. To achieve high-performance neuromorphic computing ability, a huge number of artificial synapses should be integrated because the human brain has a huge number of synapses (≈10¹⁵). In this study, a coplanar synaptic, thin-film transistor (TFT) made of c-axis-aligned crystalline indium gallium tin oxide (CAAC–IGTO) is developed. The electrical characteristics of the biological synapses such as inhibitory postsynaptic current (IPSC), paired-pulse depression (PPD), short-term plasticity (STP), and long-term plasticity at V_DS = 0.1 V, are demonstrated. The measured synaptic behavior can be explained by the migration of positively charged oxygen vacancies (V_o⁺/V_o⁺⁺) in the CAAC–IGTO layer. The mechanism of implementing synaptic behavior is completely new, compared to previous reports using electrolytes or ferroelectric gate insulators. The advantage of this device is to use conventional gate insulators such as SiO₂ for synaptic behavior. Previous studies use chitosan, Ta₂O₃, SiO₂ nanoparticles , Gd₂O₃, and HfZrO_x for gate insulators, which cannot be used for high integration of synaptic devices. The metal–oxide TFTs, widely used in the display industry, can be applied to the synaptic transistors. Therefore, CAAC–IGTO synaptic TFT can be a good candidate for application as an artificial synapse for highly integrated neuromorphic chips.     

Scalable Synthesis of Ultrathin Mn3N2 Exhibiting Room‐Temperature Antiferromagnetism

Ultrathin and 2D magnetic materials have attracted a great deal of attention recently due to their potential applications in spintronics. Only a handful of stable ultrathin magnetic materials have been reported, but their high‐yield synthesis remains a challenge. Transition metal (e.g., manganese) nitrides are attractive candidates for spintronics due to their predicted high magnetic transition temperatures. Here, a lattice matching synthesis of ultrathin Mn₃N₂ is employed. Taking advantage of the lattice match between a KCl salt template and Mn₃N₂, this method yields the first ultrathin magnetic metal nitride via a solution‐based route. Mn₃N₂ flakes show intrinsic magnetic behavior even at 300 K, enabling potential room‐temperature applications. This synthesis procedure offers an approach to the discovery of other ultrathin or 2D metal nitrides.     

Organic Field Effect Transistor-Based Photonic Synapses: Materials,Devices, and Applications

Photonic artificial synapses-based neuromorphic computing systems have been regarded as promising candidates for replacing von Neumann-based computing systems due to the high bandwidth, ultrafast signal transmission, low energy consumption, and wireless communication. Although significant progress has been made in developing varied device structures for synaptic emulation, organic field-effect transistors (OFETs) hold the compelling advantages of facile preparation, liable integration, and versatile structures. As a powerful and effective platform for photonic synapses, OFETs can fulfill not only the simulation of simple synaptic functions, but also complex photoelectric dual modulation and simulation of the visual system. Herein, an overview of OFET-based photonic synapses, including functional materials, device configurations, and innovative applications is provided. Meanwhile, rules for selecting materials, mechanism of photoelectric conversion, and fabrication techniques of devices are also highlighted. Finally, challenges and opportunities are all discussed, providing solid guidance for multilevel memory, multi-functional tandem artificial neural system, and artificial intelligence.     

基于自旋电子学的太赫兹波产生方法

自旋电子学的某些物理现象,如交换型磁振子、反铁磁共振、超快自旋动力学等,其特征频率刚好处于太赫兹频段。利用相应的自旋电子学现象和原理,研究人员发现和建立了若干新型的太赫兹波产生方法,为新型太赫兹源的实现和发展提供指导方向。这些新型产生方法有:a)自旋注入产生太赫兹波;b)基于反铁磁共振的太赫兹波产生;c)基于超快自旋动力学的太赫兹波产生。理论及实验结果表明,基于自旋电子学的太赫兹产生方法具有较大的潜力,有望推动太赫兹技术的发展。     

Sn-Based Self-Powered Ultrafast Perovskite Photodetectors with Highly Crystalline Order for Flexible Imaging Applications

Sn-based perovskite materials are promising lead-free alternatives in thin film photodetectors (PDs) for applications such as optical communications, night visions and biomedical near-infrared imaging systems. However, constructing Sn-based photodetectors with high sensitivity, ultrafast response, and good operation stability has been a challenge. Herein, the phenyl-ethyl ammonium (PEA⁺) additive is introduced in pristine FASnI₃, which regulates the thin film growth, passivates the trap/defect states, prevents Sn²⁺/Sn⁴⁺oxidation, and releases the crystal strain. The Resulting FA_0.8PEA_0.2SnI₃ thin films exhibit highly crystalline order and flexibility. A self-powered PD using FA_0.8PEA_0.2SnI₃ as the active layer demonstrates excellent responsivity of 0.262 W⁻¹, detectivity of 2.3 × 10¹¹ Jones. And it possesses the fastest rise and decay time of 25 µs and 42 µs as compared with the state-of-art Sn-based perovskite PDs. The transient absorption spectroscopy analysis validates greatly reduced trapping states and defects of FASnI₃ with the PEA⁺ film for ultrafast response. A flexible Sn-based perovskite PD without any encapsulation in air continuously shows ultrafast responses after 10,000 bending cycles. Meanwhile, a flexible imaging system can be realized by a 5 × 5 PD array with good sensing results. This study shows great potential in nontoxic and ultrafast Sn-based perovskite PDs for flexible imaging applications.     

Ultrathin Epitaxial Ferromagnetic γ‐Fe2O3 Layer as High Efficiency Spin Filtering Materials for Spintronics Device Based on Semiconductors

In spintronics, identifying an effective technique for generating spin‐polarized current has fundamental importance. The spin‐filtering effect across a ferromagnetic insulating layer originates from unequal tunneling barrier heights for spin‐up and spin‐down electrons, which has shown great promise for use in different ferromagnetic materials. However, the low spin‐filtering efficiency in some materials can be ascribed partially to the difficulty in fabricating high‐quality thin film with high Curie temperature and/or partially to the improper model used to extract the spin‐filtering efficiency. In this work, a new technique is successfully developed to fabricate high quality, ferrimagnetic insulating γ‐Fe₂O₃ films as spin filter. To extract the spin‐filtering effect of γ‐Fe₂O₃ films more accurately, a new model is proposed based on Fowler–Nordheim tunneling and Zeeman effect to obtain the spin polarization of the tunneling currents. Spin polarization of the tunneled current can be as high as ?94.3% at 2 K in γ‐Fe₂O₃ layer with 6.5 nm thick, and the spin polarization decays monotonically with temperature. Although the spin‐filter effect is not very high at room temperature, this work demonstrates that spinel ferrites are very promising materials for spin injection into semiconductors at low temperature, which is important for development of novel spintronics devices.     

Artificial Optoelectronic Synapses Based on TiNxO2–x/MoS2 Heterojunction for Neuromorphic Computing and Visual System

Being capable of dealing with both electrical signals and light, artificial optoelectronic synapses are of great importance for neuromorphic computing and are receiving a burgeoning amount of interest in visual information processing. In this work, an artificial optoelectronic synapse composed of Al/TiN_xO_2–x/MoS₂/ITO (H-OSD) is proposed and experimentally realized. The H-OSD can enable basic electrical voltage-induced synaptic functions such as the long/short-term plasticity and moreover the synaptic plasticity can be electrically adjusted. In response to the light stimuli, versatile advanced synaptic functions including long/short-term memory, and learning-forgetting-relearning are successfully demonstrated, which could enhance the information processing capability for neuromorphic computing. Most importantly, based on these light-induced salient features, a 4 × 4 synapse array is developed to show the potential application of the proposed H-OSD in constructing artificial visual system. It is shown that the perceiving and memorizing of the light information that are respectively relevant to the visual perception and visual memory functions, can be readily attained through tuning of the light intensity and the number of illuminations. As such, the proposed optoelectronic synapse shows great potentials in both neuromorphic computing and visual information processing and will facilitate the applications such as electronic eyes and light-driven neurorobotics.     

Dual‐Phase All‐Inorganic Cesium Halide Perovskites for Conducting‐Bridge Memory‐Based Artificial Synapses

Neuromorphic computing, which mimics biological neural networks, can overcome the high‐power and large‐throughput problems of current von Neumann computing. Two‐terminal memristors are regarded as promising candidates for artificial synapses, which are the fundamental functional units of neuromorphic computing systems. All‐inorganic CsPbI₃ perovskite‐based memristors are feasible to use in resistive switching memory and artificial synapses due to their fast ion migration. However, the ideal perovskite phase α‐CsPbI₃ is structurally unstable at ambient temperature and rapidly degrades to a non‐perovskite δ‐CsPbI₃ phase. Here, dual‐phase (Cs₃Bi₂I₉)_0.4?(CsPbI₃)_0.6 is successfully fabricated to achieve improved air stability and surface morphology compared to each single phase. Notably, the Ag/polymethylmethacrylate/(Cs₃Bi₂I₉)_0.4?(CsPbI₃)_0.6/Pt device exhibits non‐volatile memory functions with an endurance of ≈10³ cycles and retention of ≈10⁴ s with low operation voltages. Moreover, the device successfully emulates synaptic behavior such as long‐term potentiation/depression and spike timing/width‐dependent plasticity. This study will contribute to improving the structural and mechanical stability of all‐inorganic halide perovskites (IHPs) via the formation of dual phase. In addition, it proves the great potential of IHPs for use in low‐power non‐volatile memory devices and electronic synapses.     

A Nanozyme-Based Artificial Peroxisome Ameliorates Hyperuricemia and Ischemic Stroke

Artificial peroxisome has drawn a lot of attentions for its usefulness in fabricating protocell system and great potential in treating diseases. However, it is still a significant challenge to prepare a practicable artificial peroxisome to complement multiple and stable functions under physiological condition. Herein, a novel strategy is reported to design an artificial peroxisome using a nanozyme to accommodate multiple enzyme-like activities that mimics those enzymes in natural peroxisome. The enzymatic active sites are introduced into graphitized moieties on the shell of a hollow carbon nanozyme by doping iron and nitrogen to form Fe–N₄ coordination and atomic Fe cluster. With Fe clusters as reversible cofactors and Fe–N₄ as prosthetic group, the resulted carbon nanozyme exhibits stable and multiple peroxisomal-like activities, including catalase, uricase, superoxide dismutase, peroxidase, and oxidase, which is referred as nanozyme-based artificial peroxisome (pero-nanozysome). This pero-nanozysome shows therapeutic effect for treating hyperuricemia and protecting neurons from free radicals generated during ischemic stroke by employing the tandem activities of uricase-catalase and superoxide-dismutase-catalase, respectively. This study indicates that the pero-nanozysome is a promising candidate to design artificial peroxisome performing in vivo functions.     

共振混频过程的超快弛豫现象研究

本文报导利用共振混频过程,可在不利用超短脉冲激光情况下对皮秒甚至飞秒量级的超快弛豫进行测量。采用密度矩阵方法对该混频过程的二能级系统的非线性极化率XR进行了计算,结果表明过程的频率特性与样品的纵向弛豫时间T1和横向弛豫时间T2有关。实验测量得到孔雀绿水溶液的T1和T2分别为1.20ps和0.09ps。     

Printed Neuromorphic Devices Based on Printed Carbon Nanotube Thin‐Film Transistors

Hardware implementation of artificial synapse/neuron by electronic/ionic hybrid devices is of great interest for brain‐inspired neuromorphic systems. At the same time, printed electronics have received considerable interest in recent years. Here, printed dual‐gate carbon‐nanotube thin‐film transistors with very high saturation field‐effect mobility (≈269 cm² V^?1 s^–1) are proposed for artificial synapse application. Some important synaptic behaviors including paired‐pulse facilitation (PPF), and signal filtering characteristics are successfully emulated in such printed artificial synapses. The PPF index can be modulated by spike width and spike interval of presynaptic impulse voltages. The results present a printable approach to fabricate artificial synaptic devices for neuromorphic systems.     

Spin-Dependent Charge Transport in 1D Chiral Hybrid Lead-Bromide Perovskite with High Stability

Spin-dependent charge transport, along with the potential electronic applications, is investigated in chiral 2D iodide hybrid organic/inorganic perovskites (HOIPs) via the chirality-induced spin selectivity (CISS) effect, paving a new way in spintronics. Despite the high spin-polarized current enhancement, the intrinsic oxidation tendency of iodide ions brings about severe problems in the stability and lifetime of electronic devices. Here, spin-dependent charge transport properties in lead-bromide perovskites hybrid with chiral R/S-methylbenzylammonium (MBA), that is, (R/S-MBA)PbBr₃ are explored. Distinct from layered 2D iodide perovskites (R/S-MBA)₂PbI₄ which experience obvious crystal degradation along time, (R/S-MBA)PbBr₃ maintain good crystallinity even in the oxidative, humid, and high-temperature environment due to the lower Fermi level of bromide than iodide. Magnetic conductive atomic force microscopy displays a spin filtration efficiency as high as 90%, showing negligible decay after 1 month. This work expands the spin transport to chiral bromide perovskites with higher stability, and thus provides significant support for the practical application of HOIPs in spintronics.     

Electrolyte-gated transistors for neuromorphic applications

Von Neumann computers are currently failing to follow Moore’s law and are limited by the von Neumann bottleneck.To enhance computing performance,neuromorphic computing systems that can simulate the function of the human brain are being developed.Artificial synapses are essential electronic devices for neuromorphic architectures,which have the ability to perform signal processing and storage between neighboring artificial neurons.In recent years,electrolyte-gated transistors(EGTs)have been seen as promising devices in imitating synaptic dynamic plasticity and neuromorphic applications.Among the various electronic devices,EGT-based artificial synapses offer the benefits of good stability,ultra-high linearity and repeated cyclic symmetry,and can be constructed from a variety of materials.They also spatially separate“read”and“write”operations.In this article,we provide a review of the recent progress and major trends in the field of electrolyte-gated transistors for neuromorphic applications.We introduce the operation mechanisms of electric-double-layer and the structure of EGT-based artificial synapses.Then,we review different types of channels and electrolyte materials for EGT-based artificial synapses.Finally,we review the potential applications in biological functions.     

Study of front-side connected chemical field effect transistor for water analysis

Front-side connected, N-channel, normally-off, chemical field effect transistor (ChemFET) microsensors including a SiO₂/Si₃N₄ pH-sensitive gate have been fabricated using a standard P-well silicon technology. The fabrication and packaging processes are described and sensor properties and performances are demonstrated through pH measurements. Finally, the front-side connected ChemFETs microsensors have been adapted to the detection of ions thanks to polyHEMA/siloprene-based ionosensitive membranes. Application is performed through the NH₄⁺ and NO₃⁻ ions detection in artificial solutions, evidencing quasi-Nernstian responses (s≈50 mV/pH) in the appropriate detection ranges. This microsensor will be used for the monitoring of environmental pollution and more precisely for ground water analysis.