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Owing to the unique features of low Gilbert damping, long spin‐diffusion lengths, and zero Ohmic losses, magnetic insulators are promising candidate materials for next‐generation spintronic applications. However, due to the localized magnetic moments and the complex metal–oxide interface between magnetic insulators and heavy metals, spin‐functional Dzyaloshinskii–Moriya interactions or spin Hall and Edelstein effects are weak, which diminishes the performance of these typical building blocks for spintronic devices. Herein, the exchange coupling between metallic and insulating magnets is exploited for efficient electrical manipulation of heavy metal/magnetic insulator heterostructures. By inserting a thin Co layer, the spin‐orbit torque efficiency is enhanced by more than 20 times, which significantly reduces the switching current density. Moreover, field‐free current‐induced magnetization switching caused by a symmetry‐breaking non‐collinear magnetic texture is demonstrated. This work launches magnetic insulators as an alternative platform for low‐power spintronic devices. [ABSTRACT FROM AUTHOR]

A method of using non‐volatile and fast ferroelectric field‐effect transistor (FeFET) devices to realize Boolean logic is proposed. First, the internal states are initialized. Then, the gate and body function as input terminals, which are used to write the states of the device, based on the voltage. Finally, the output signals can be easily read through the drain current. Of the 10 Institute of Electrical and Electronics Engineers (IEEE) standard logic gates, eight can be implemented using the proposed operation method alone and by following the definitions listed herein. Thus, to enable FeFET devices to act as functional logic gates, a simple operating method is proposed, providing substantial contributions to the development of computing in memory. The experimental results provide evidence of the efficacy of this method. [ABSTRACT FROM AUTHOR]

The memristor is a resistive switch where its resistive state is programable based on the applied voltage or current. Memristive devices are thus capable of storing and computing information simultaneously, breaking the Von Neumann bottleneck. Since the first nanomemristor made by Hewlett‐Packard in 2008, advances so far have enabled nanostructured, low‐power, high‐durability devices that exhibit superior performance over conventional CMOS devices. Herein, the development of memristors based on different physical mechanisms is reviewed. In particular, device stability, integration density, power consumption, switching speed, retention, and endurance of memristors, that are crucial for neuromorphic computing, are discussed in detail. An overview of various neural networks with a focus on building a memristor‐based spike neural network neuromorphic computing system is then provided. Finally, the existing issues and challenges in implementing such neuromorphic computing systems are analyzed, and an outlook for brain‐like computing is proposed. [ABSTRACT FROM AUTHOR]

Electrical manipulation of exchange bias (EB) enables an additional degree of freedom in the design of innovative spintronic devices. However, the electrical switching of EB via spin–orbit torque (SOT) has not been achieved in magnetic tunnel junctions (MTJs), which are one of the building blocks in spintronic devices. Herein, based on the SOT in antiferromagnets (AFMs), perpendicular EB reversal across AFM IrMn and ferromagnetic (FM) [Co/Pt]2 multilayer is demonstrated both in extended and confined geometries. In particular, in three‐terminal perpendicular MTJ devices, the switching of the EB using the SOT is achieved. Both high and low resistances are observed at the zero magnetic field during EB switching. The findings provide the direction to include a new functionality in spintronic devices and will inspire future research in exploring the electrical control of EB in SOT magnetic random access memory (SOT‐MRAM). [ABSTRACT FROM AUTHOR]

To solve the von Neumann performance bottleneck, many kinds of magnetic logic devices are proposed. However, the operation speed, power consumption, and error rate of these devices are incompatible with complementary metal−oxide−semiconductor (CMOS) logic, and moreover, cascading of the devices is difficult. Herein, instead, a new voltage‐dominated magnetic logic‐memory device is proposed, with switching time of 300 ps and power consumption of 150 fJ, representing ≈10 times improvement compared with CMOS logic on the same scale. The device has a reliable output ratio of >3000%, a low working magnetic field of <10 mT, and a low error rate of ≈10−7. Moreover, complex logic operations, such as XOR gates and a full adder, can be realized using this device via cascading. As a result of these advantages, the magnetic logic‐memory device is well suited for practical applications. [ABSTRACT FROM AUTHOR]

As semiconductor technology enters the more than Moore era, there exists an apparent contradiction between the rapidly growing demands for data processing and the visible inefficiency rooted in traditional computing architecture. Neuromorphic systems hold great prospects in enabling a new generation of computing paradigm that can address this issue, which demands device components with rich dynamics and nonlinearity. Herein, the nonlinearity in memristive devices and their application in building neuromorphic dynamic systems are reviewed. The internal mechanisms that endow memristive devices with nonlinearity and rich dynamics are reviewed and subsequently the nonlinear spiking neurons that are implemented utilizing the physical processes in memristors are shown. Typical examples on neuromorphic dynamic systems based on nonlinear memristors are summarized, including memristive reservoir, memristive oscillatory neural network, and memristive chaotic computing. Finally, an outlook in the development of neuromorphic dynamic systems is given. [ABSTRACT FROM AUTHOR]

Nanometer‐thick Co–Fe–B/MgO based structures have been widely accepted as the preferred system for immediate and long‐term goals in magnetic random access memory (MRAM) devices because of excellent spin‐torque efficiency and promise for high‐density MRAM. To realize next‐generation ultra‐low‐power MRAM, further lowering of power consumption in these structures is a crucial ongoing effort. Gilbert damping is one critical material parameter toward lowering energy consumption but is traditionally large (≈10−2) in these Co–Fe–B/MgO systems. Here, Gilbert damping of (1.3 ± 0.3) × 10−3 from a perpendicular double Co–Fe–B/MgO interface system engineered at different boron compositions is reported. Remarkably, this value is achieved with ≈1 nm of Co–Fe–B thickness while maintaining magnetic anisotropy of 0.4 Merg cc−1. An unusual damping trend that scales with layer thickness in high‐boron content films established from both experiments and first‐principles calculations is reported. [ABSTRACT FROM AUTHOR]

From Deep Blue to AlphaGo, artificial intelligence and machine learning are booming, and neural networks have become the hot research direction. However, due to the size limit of complementary metal–oxide–semiconductor (CMOS) transistors, von Neumann‐based computing systems are facing multiple challenges (such as memory walls). As the number of transistors required by the neural network increases, the development of neural networks based on the von Neumann computer is limited by volume and energy consumption. As the fourth basic circuit element, memristor shines in the field of neuromorphic computing. The new computer architecture based on memristor is widely considered as a substitute for the von Neumann architecture and has great potential to deal with the neural network and big data era challenge. This article reviews existing materials and structures of memristors, neurophysiological simulations based on memristors, and applications of memristor‐based neural networks. The feasibility and advancement of implementing neural networks using memristors are discussed, the difficulties that need to be overcome at this stage are put forward, and their development prospects and challenges faced are also discussed. [ABSTRACT FROM AUTHOR]

One of the critical issues in spintronics‐based technologies is to increase the data storage density. Current strategy is based on shrinking the devices size down to tens of nanometers, or several nanometers, which is reaching its limit. A new proposal is to use multi‐level cells (MLCs) to store more than two bits in each cell. In this work, the multi‐level switching is realized in CoFeB/MgO/CoFeB based nano‐scale single perpendicular magnetic tunnel junctions (p‐MTJs) with three or four stable resistance states. A large range of writing currents for each state is obtained, accompanying with a good repeatability of set‐reset operations between different states. The developed multi‐domain model perfectly matches the experimental results, reflecting the magnetic behaviors during multi‐level switching. Furthermore, current‐driven domain wall (DW) motion is revealed in the circular p‐MTJs, where the DW position can be reversibly manipulated by applied current. To design high‐performance multi‐level p‐MTJs, the parameter diagrams are calculated, suggesting various feasible strategies to improve the multi‐level switching through materials optimization and devices geometry. In summary, the demonstration of multi‐level switching in single p‐MTJ shows the high potential of realizing the new generation of p‐MTJ‐based multi‐level spintronic devices, such as multi‐level memories and spin‐neuron devices. [ABSTRACT FROM AUTHOR]

In complementary metal–oxide–semiconductor (CMOS)‐based von Neumann architectures, the intrinsic power and speed inefficiencies are worsened by the drastic increase in information with big data. With the potential to store numerous values in I–V pinched hysteresis, memristors (memory resistors) have emerged as alternatives to existing CMOS‐based computing systems. Herein, four types of memristive devices, namely, resistive switching, phase‐change, spintronics, and ferroelectric tunnel junction memristors, are explored. The application of these devices to a crossbar array (CBA), which is a novel concept of integrated architecture, is a step toward the realization of ultradense electronics. Exploiting the fascinating capabilities of memristive devices, computing systems can be developed with novel computing paradigms, in which large amounts of data can be stored and processed within CBAs. Looking further ahead, the ways in which memristors could be incorporated in neuromorphic computing systems along with various artificial intelligence algorithms are established. Finally, perspectives and challenges that memristor technology should address to provide excellent alternatives to existing computing systems are discussed. The infinite potential of memristors is the key to unlock new computing paradigms, which pave the way for next‐generation computing systems. [ABSTRACT FROM AUTHOR]

The economical, agile, customizable manufacturing, and integration of multifunctional device modules into networked systems with mechanical compliance and robustness enable unprecedented human‐integrated smart wearables and usher in exciting opportunities in emerging technologies. The additive manufacturing (AM) processes have emerged as potential candidates for rapid prototyping printed devices with diversified functionalities, e.g., energy harvesting/storage, sensing, actuation, and computation. However, there are few review reports about the ink‐based additive nanomanufacturing of functional materials for human‐integrated smart wearables. To fill this gap, herein, the recent progress in ink‐based additive nanomanufacturing technologies, focusing on their capability and potential for producing wearable human‐integrated devices, is reviewed. The manufacturing process integration, functional materials, device implementation, and application performance issues in designing and implementing the ink‐based additively nanomanufactured wearable systems are thoroughly discussed. The recent printed devices focusing on the processing conditions and performance metrics are comprehensively reviewed. Finally, the vision and outlook for the challenges and opportunities associated with related topics are provided. The rapid progress achieved in related disciplines enables more capable smart human‐integrated wearable systems that can be fully printed with rapid, agile, reconfigurable, and smart AM platforms. [ABSTRACT FROM AUTHOR]

A strong perpendicular magnetic anisotropy (PMA) and a high thermal stability are essential for long‐term stable storage of data in PMA‐based magnetic tunnel junctions (p‐MTJs). This work investigates the magnetic anisotropy of the MgO/CoFeB/X/CoFeB/MgO double‐interface free layer stacks, where X represents the spacer material. After annealing at 350 °C for an hour, interfacial magnetic anisotropy (Ki) as high as 4.06 mJ m−2 is obtained in the MgO/CoFeB/Mo (0.4 nm)/CoFeB/MgO stacks, much higher than those for Ta‐ and W‐based films. Experimental and first‐principle calculation results demonstrate that bulk PMA plays a great role in the Mo‐based structure, which is often negligible in Ta‐ and W‐based structures. Moreover, a strong PMA is achieved after annealing at 500 °C, which is attributed to the weak interdiffusion and good uniformity as shown in high‐resolution transmission electron microscopy and energy‐dispersive X‐ray spectroscopy results. These findings help to understand the origin of strong PMA in Mo‐based structures and show the promising prospect of using this structure for high‐packing‐density p‐MTJs and other spintronic device applications down to 10 nm scale. [ABSTRACT FROM AUTHOR]

This paper extends the applicability of the micro four‐point probe technique from the sheet resistance measurements on large areas toward narrow (<20 nm) semiconducting nanostructures with an elongated fin geometry. Using this technology, it is shown that the sheet resistance of boron‐implanted and laser‐annealed silicon fins with widths ranging from 500 down to 20 nm rises as the width is reduced. Drift‐diffusion simulations show that the observed increase can be partially explained by the carrier depletion induced by interface states at the fin sidewalls. [ABSTRACT FROM AUTHOR]

Spin transfer torque (STT) switching-based magnetic random access memory (MRAM) is gaining significant industrial and academic attention due to its potential application as a non-volatile memory device in computing devices, smartphones, and so on. STT-MRAM devices with in-plane magnetization configuration have been marketed as niche products. Devices with out-of-plane magnetization are being considered for embedded memory as the first step. Aggressive goals include replacing dynamic random access memory (DRAM) with STT-MRAM. This review article introduces the basics of STT-MRAM and describes the recent progress in overcoming certain challenges such as reduction of power consumption and increase of storage density, which will make it a strong competitor for DRAM. [ABSTRACT FROM AUTHOR]

Graphene and related materials (GRMs) are promising candidates for the fabrication of resistive random access memories (RRAMs). Here, this emerging field is analyzed, classified, and evaluated, and the performance of a number of RRAM prototypes using GRMs is summarized. Graphene oxide, amorphous carbon films, transition metal dichalcogenides, hexagonal boron nitride and black phosphorous can be used as resistive switching media, in which the switching can be governed either by the migration of intrinsic species or penetration of metallic ions from adjacent layers. Graphene can be used as an electrode to provide flexibility and transparency, as well as an interface layer between the electrode and dielectric to block atomic diffusion, reduce power consumption, suppress surface effects, limit the number of conductive filaments in the dielectric, and improve device integration. GRM-based RRAMs fit some non-volatile memory technological requirements, such as low operating voltages (<1V) and switching times (<10 ns), but others, like retention >10 years, endurance >109 cycles and power consumption ≈10 pJ per transition still remain a challenge. More technology-oriented studies including reliability and variability analyses may lead to the development of GRMs-based RRAMs with realistic possibilities of commercialization. [ABSTRACT FROM AUTHOR]

General drawbacks of current electronic/spintronic devices are high power consumption and low density storage. A multiferroic tunnel junction (MFTJ), employing a ferroelectric barrier layer sandwiched between two ferromagnetic layers, presents four resistance states in a single device and therefore provides an alternative way to achieve high density memories. Here, an MFTJ device with eight nonvolatile resistance states by further integrating the design of noncollinear magnetization alignments between the ferromagnetic layers is demonstrated. Through the angle‐resolved tunneling magnetoresistance investigations on La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 junctions, it is found that, besides collinear parallel/antiparallel magnetic configurations, the MFTJ shows at least two other stable noncollinear (45° and 90°) magnetic configurations. Combining the tunneling electroresistance effect caused by the ferroelectricity reversal of the BaTiO3 barrier, an octonary memory device is obtained, representing potential applications in high density nonvolatile storage in the future. [ABSTRACT FROM AUTHOR]

We describe the comprehensive characterization of GaMnAs epitaxial thin films and magnetic tunnel junctions (MTJ) by complementary techniques ranging from high-resolution imaging to magnetometry, magnetotransport, time-resolved magneto-optics, and coplanar broadband ferromagnetic resonance (FMR). Magnetometry and magnetotransport on macroscopic samples allow deriving the saturation magnetization and quasi-static reversal fields. Perpendicular transport experiments on patterned MTJ pillars further reveal the tunneling magnetoresistance ratio. Additionally the precessional dynamics are characterized by time-resolved magneto-optics and broadband network analyzer FMR yielding the effective Gilbert damping and the sample anisotropies. The combination of the different techniques allows a comprehensive characterization of the key magnetostatic and dynamic material parameters of GaMnAs-based thin films and devices. [ABSTRACT FROM AUTHOR]

In this paper, we review the theory of spin switching for systems of different sizes, from a quantum mechanical master equation approach for small atomic clusters to the quasiclassical description of spin dynamics by a stochastic Landau-Lifshits-Gilbert equation in metallic nanoscale magnetic systems. We present characteristic results emphasizing the role of the quantum character of spin at different scales. Comparing the quantum mechanical and the quasiclassical approach to spin switching, we draw analogies between the factors affecting quantum and classical spin dynamics. We analyze assumptions used in each approach and emphasize the limits of applicability of the quantum mechanical and of the quasiclassical descriptions. [ABSTRACT FROM AUTHOR]

Magnetization switching by a spin-polarized current in perpendicular anisotropy devices with magnetic nanocontact (NC) is investigated using a micromagnetic formalism. The critical switching current ( icr) and switching time ( τ0) can be reduced when a soft layer is exchange coupled to the NC. The study reveals that devices with fewer NCs have smaller icr compared to those with a large number. Furthermore, τ0 for nanoconstricted devices is almost constant with anisotropy field ( Hk), in contrast to devices without NCs that show an exponential increase with Hk. This suggests that nanoconstricted devices could be used to improve thermal stability, while reducing icr and τ0. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Spin reorientation phase transitions (RPTs) in magnetostatically coupled low-anisotropy ultrathin multilayers (MLs) have been studied. The RPT conditions were established and applied in a simple analytical model to describe spin reorientation between in-plane and out-of-plane magnetic phases. The proposed model has been found to be in good agreement with micromagnetic simulations. It was also shown how the magnetization orientation of MLs could be manipulated by choosing their geometrical and magnetic parameters. [ABSTRACT FROM AUTHOR]

Perpendicular exchange bias (PEB) between [Co 0.3 nm/Pd 0.8 nm]5 multilayers and IrMn antiferromagnetic (AFM) layer is studied as functions of thickness of the interface layer and the AFM layer. It is found that increasing the thickness of a CoFe interface layer up to 2.1 nm could effectively improve the PEB. The achieved PEB field ( Hbias) is more than 500 Oe. On the other hand, the coercivity ( Hc) exhibits an opposite trend as a function of CoFe interface layer thickness, which might promote the integration of PEB structure with the perpendicular magnetic memory stack. It is also found that PEB is sensitive to the thickness of the AFM layer. The thickness window is only around 2 nm to achieve the largest Hbias. Moreover, for a very thin IrMn layer, a ferromagnetic nature is observed at low magnetic fields, which is likely owing to the net spins at the surface that might have been magnetized by the CoFe interface layer. [ABSTRACT FROM AUTHOR]

By means of integrated circuit (IC) process technology, a monolithic thin-film rector was fabricated on a silicon substrate with lamination of a thick-film conductor and a magnetic thin film. In addition to the fundamental characteristics of the reactor, the dynamic characteristics are evaluated when the reactor is used in a dc-dc converter. For the buck converter application, the output of more than 2 W with the efficiency of more than 70 percent is achieved. [ABSTRACT FROM AUTHOR]

In this article, the film of Sr0.775Y0.225CoO3-δ, which shows the highest ferromagnetic Curie temperature in perovskite ABO3-based cobaltates due to antiferrotype orbital order, was first prepared successfully on LaAlO3 (100) substrate using the simple chemical solution deposition (CSD) method. The results show that the derived film is (h00)-epitaxial, and the transport property is semiconductor like with room-temperature ferromagnetism (FM). The result will provide a feasible route to prepare Sr0.775Y0.225CoO3-d film with room-temperature FM using CSD with a low-cost and nonvaccum method. [ABSTRACT FROM AUTHOR]

With the widespread use of mobile computing and internet of things, secured communication and chip authentication have become extremely important. Hardware‐based security concepts generally provide the best performance in terms of a good standard of security, low power consumption, and large‐area density. In these concepts, the stochastic properties of nanoscale devices, such as the physical and geometrical variations of the process, are harnessed for true random number generators (TRNGs) and physical unclonable functions (PUFs). Emerging memory devices, such as resistive‐switching memory (RRAM), phase‐change memory (PCM), and spin‐transfer torque magnetic memory (STT‐MRAM), rely on a unique combination of physical mechanisms for transport and switching, thus appear to be an ideal source of entropy for TRNGs and PUFs. An overview of stochastic phenomena in memory devices and their use for developing security and computing primitives is provided. First, a broad classification of methods to generate true random numbers via the stochastic properties of nanoscale devices is presented. Then, practical implementations of stochastic TRNGs, such as hardware security and stochastic computing, are shown. Finally, future challenges to stochastic memory development are discussed. [ABSTRACT FROM AUTHOR]

The hysteretic behavior of organic–inorganic halide perovskites (OHPs) are exploited for application in neuromorphic electronics. Artificial synapses with 2D and quasi‐2D perovskite are demonstrated that have a bulky organic cation (phenethylammonium (PEA)) to form structures of (PEA)2MAn‐1PbnBr3n+1. The OHP films have morphological properties that depend on their structure dimensionality (i.e., n value), and artificial synapses fabricated from them show synaptic responses such as short‐term plasticity, paired‐pulse facilitation, and long‐term plasticity. The operation mechanism of OHP artificial synapses are also analyzed depending on the dimensionality and it is found that quasi‐2D (n = 3–5) OHP artificial synapses show much longer retention than 2D and 3D OHP counterparts. The calculated energy consumption of a 2D OHP artificial synapse (≈0.7 fJ per synaptic event) is comparable to that of biological synapses (1–10 fJ per synaptic event). These OHP artificial synapses may enable development of neuromorphic electronics that use very little energy. [ABSTRACT FROM AUTHOR]

Spintronic devices such as magnetic tunnel junctions and skyrmions have attracted considerable attention due to features such as nonvolatility, high scalability, low power, and high speed. Over the past few years, innovative materials and new structures in this field have resulted in the emergence of new phenomena and exciting device performance. It has been found that the heavy metal (HM)/ferromagnetic metal (FM) interface plays an essential role in spintronic devices. Spintronic device performance can be significantly enhanced through proper modulation of this interface. Recent progress in this blooming field is reviewed with specific emphasis on the HM/FM interface. Investigations into HM/FM‐interface‐related phenomena, including perpendicular magnetic anisotropy, tunnel magnetoresistance, magnetic damping, spin–orbit torque, and Dzyaloshinskii–Moriya interaction, are put into context. Guidelines for realizing high‐performance spintronic devices are provided, and an outlook on their future research direction and potential applications is given. [ABSTRACT FROM AUTHOR]

Realization of sub‐10 nm spin‐based logic and memory devices relies on the development of magnetic materials with perpendicular magnetic anisotropy that can provide low switching current and large thermal stability simultaneously. In this work, the authors report on one promising candidate, Fe16N2, a heavy‐metal‐free, non‐interface perpendicular magnetic material and demonstrate a perpendicularly magnetized current‐perpendicular‐to‐plane (CPP) giant magnetoresistance (GMR) device based on Fe16N2. The crystalline‐based perpendicular anisotropy of Fe16N2 in the CPP GMR device is measured to be about 1.9 × 106 J m−3 (1.9 × 107 erg cm−3), which is sufficient to maintain the thermal stability of sub‐10 nm devices. A first principle calculation is performed to support this large magnitude of the perpendicular anisotropy. Moreover, the Gilbert damping constant of the Fe16N2 thin film (α ≈0.01) measured by ferromagnetic resonance (FMR) is lower than for most existing materials with crystalline perpendicular magnetic anisotropy. The non‐interface perpendicular anisotropy and low damping properties of Fe16N2 may offer a pathway for future spintronics logic and memory devices. [ABSTRACT FROM AUTHOR]

Cobalt ferrite ferrimagnetic nanoparticles (NPs) are prepared and used in this work as seeds to grow a thin antiferromagnetic poly‐ and nanocrystalline CoO shell. The major purpose is to study systematically the characteristics of the as‐produced powders, making emphasis on their internal crystallographic arrangement and their magnetic properties. 57Fe Mössbauer spectrometry evidences an evolution of the cation distribution among the spinel lattice in the cobalt ferrite core during the core–shell NPs processing. High‐resolution transmission electron microscopy shows a perfect epitaxy between the face‐centered cubic lattices of the spinel core and the rock‐salt shell. Finally, the measurements of 7T‐field‐cooled magnetic hysteresis loops at low temperature (5 K) of the composite particles exhibit a strong exchange bias coupling with an exchange field, µ0HE, of 365 mT and an enhanced coercive field, µ0HC, of 1395 mT. These values are very high compared to those of differently prepared CoO‐based oxide composite NPs and for which a giant exchange‐bias is reported. These features are attributed to the favorable material processing conditions offered by the polyol process in terms of crystalline quality, particularly at the interfaces, and for the pinning action exerted by the CoO phase on the magnetization of the CoFe2O4 phase. Oxide‐based core–shell like nanoparticles are produced by the polyol process. Their advanced structural and microstructural characterization highlighted their very exceptional crystallographic quality, making them able to exhibit giant EB feature. [ABSTRACT FROM AUTHOR]