Majority logic gate for magnetic quantum-dot cellular automata

Realization of inverse-design magnonic logic gates

Magnonic logic gates represent a crucial step toward realizing fully magnonic data processing systems without reliance on conventional electronic or photonic elements. Recently, a universal and reconfigurable inverse-design device has been developed, featuring a 7 by 7 array of independent current loops that create local inhomogeneous magnetic fields to scatter spin waves in an yttrium-iron-garnet film. Although initially used for linear radio frequency components, we now demonstrate key nonlinear logic gates, NOT, OR, NOR, AND, NAND, and a half-adder, sufficient for building a full processor. In this system, binary data ("0" and "1") are encoded in the spin-wave amplitude. The contrast ratio, representing the difference between logic states, achieved values of 34, 53.9, 11.8, 19.7, 17, and 9.8 decibels for these gates, respectively.

Ultraflexible Sensor Development via 4D Printing: Enhanced Sensitivity to Strain, Temperature, and Magnetic Fields

This paper addresses the trade-off between sensitivity and sensing range in strain sensors, while introducing additional functionalities through an innovative 4D printing approach. The resulting ultraflexible sensor integrates carbon nanotubes/liquid metal hybrids and iron powders within an Ecoflex matrix. The optimization of this composition enables the creation of an uncured resin ideal for Direct Ink Writing (DIW) and a cured sensor with exceptional electromechanical, thermal, and magnetic performance. Notably, the sensor achieves a wide linear strain range of 350% and maintains a stable Gauge Factor of 19.8, offering an ultralow detection limit of 0.1% strain and a rapid 83-ms response time. Beyond superior strain sensing capabilities, the sensor exhibits outstanding thermal endurance for temperatures exceeding 300 °C, enhanced thermal conductivity, and a consistent resistance-temperature relationship, making it well-suited for high-temperature applications. Moreover, the inclusion of iron particles provides magnetic responsiveness, enabling synergistic applications in location and speed detection, particularly in home care. Leveraging DIW facilitates the creation of complex-shaped sensors with multiple functional materials, significantly broadening the sensor's capabilities. This convergence of additive manufacturing and multifunctional materials marks a transformative step in advancing the performance of next-generation sensors across diverse domains.

Magnetic Domain Wall Energy Landscape Engineering in a Ferrimagnet

Architectures based on a magnetic domain wall (DW) can store and process information at a high speed in a nonvolatile manner with ultra-low power consumption. Recently, transition-metal rare earth metal alloy-based ferrimagnets have attracted a considerable amount of attention for the ultrafast current-driven DW motion. However, the high-speed DW motion is subject to film inhomogeneity and device edge defects, causing challenges in controlling the DW motion and hindering practical application. In this work, we demonstrate a strategy for precisely engineering the DW energy landscape by locally modifying the compensation state in a ferrimagnet via ion irradiation by using the focused ion beam technique. A diode-like DW motion behavior is observed at the lateral junction interface, i.e., the boundary between irradiated and non-irradiated CoGd, enabling selective control over DW pinning and depinning at specific locations. Our work provides insight into the development of next-generation DW-based ferrimagnetic racetrack memory and logic devices.

Critical metrology of minimally accessible anisotropic spin chains

We address quantum metrology in critical spin chains with anisotropy and Dzyaloshinskii-Moriya (DM) interaction, and show how local and quasi-local measurements may be exploited to characterize global properties of the systems. In particular, we evaluate the classical (magnetization) and quantum Fisher information of the relevant parameters for the density matrix of a single spin and that of a pair of spins ranging from nearest to sixth-nearest neighbors, to the limiting case of very distant spins. Our results allow us to elucidate the role of the different parameters and to individuate the optimal working regimes for the precise characterization of the system, also clarifying the effects of correlations on the estimation precision.

Magnetization dynamics in single and trilayer nanowires

We have studied the magnetization dynamics of single Py(t) (t= 20 nm, 50 nm) and trilayer [Py(50)/Pd(tPd)/Py(20)] nanowire arrays fabricated over large areas using deep ultraviolet lithography technique. The dynamic properties are sensitive to the field orientation and magnetic film thicknesses. A single resonant mode corresponding to the excitations at the bulk part of the wire is detected in all the single-layer nanowire arrays. Furthermore, the spacer layer thickness influenced the dynamic properties in trilayer samples due to the different coupling mechanisms. A single resonant mode is observed intPd= 2 nm trilayer nanowires with a sharp frequency jump from 13 GHz to 15 GHz across the reversal regime. This indicates the exchange coupling and the coherence in magnetization precession in the ferromagnetic layers. On the other hand, wires with 10 nm-spacer display two well-resolved modes separated by ∼3 GHz with a gradual change in frequency across the reversal regime from-26mT to-46mT, indicating the presence of long-range dipolar interactions instead of exchange coupling. The spacer layer of the proposed spin-valve-type structure can be tailored for desired microwave splitters or combiners.

Progress in Spin Logic Devices Based on Domain-Wall Motion

Spintronics, utilizing both the charge and spin of electrons, benefits from the nonvolatility, low switching energy, and collective behavior of magnetization. These properties allow the development of magnetoresistive random access memories, with magnetic tunnel junctions (MTJs) playing a central role. Various spin logic concepts are also extensively explored. Among these, spin logic devices based on the motion of magnetic domain walls (DWs) enable the implementation of compact and energy-efficient logic circuits. In these devices, DW motion within a magnetic track enables spin information processing, while MTJs at the input and output serve as electrical writing and reading elements. DW logic holds promise for simplifying logic circuit complexity by performing multiple functions within a single device. Nevertheless, the demonstration of DW logic circuits with electrical writing and reading at the nanoscale is still needed to unveil their practical application potential. In this review, we discuss material advancements for high-speed DW motion, progress in DW logic devices, groundbreaking demonstrations of current-driven DW logic, and its potential for practical applications. Additionally, we discuss alternative approaches for current-free information propagation, along with challenges and prospects for the development of DW logic.

Atomically precise vacancy-assembled quantum antidots

Patterning antidots, which are regions of potential hills that repel electrons, into well-defined antidot lattices creates fascinating artificial periodic structures, leading to anomalous transport properties and exotic quantum phenomena in two-dimensional systems. Although nanolithography has brought conventional antidots from the semiclassical regime to the quantum regime, achieving precise control over the size of each antidot and its spatial period at the atomic scale has remained challenging. However, attaining such control opens the door to a new paradigm, enabling the creation of quantum antidots with discrete quantum hole states, which, in turn, offer a fertile platform to explore novel quantum phenomena and hot electron dynamics in previously inaccessible regimes. Here we report an atomically precise bottom-up fabrication of a series of atomic-scale quantum antidots through a thermal-induced assembly of a chalcogenide single vacancy in PtTe2. Such quantum antidots consist of highly ordered single-vacancy lattices, spaced by a single Te atom, reaching the ultimate downscaling limit of antidot lattices. Increasing the number of single vacancies in quantum antidots strengthens the cumulative repulsive potential and consequently enhances the collective interference of multiple-pocket scattered quasiparticles inside quantum antidots, creating multilevel quantum hole states with a tunable gap from the telecom to far-infrared regime. Moreover, precisely engineered quantum hole states of quantum antidots are geometry protected and thus survive on oxygen substitutional doping. Therefore, single-vacancy-assembled quantum antidots exhibit unprecedented robustness and property tunability, positioning them as highly promising candidates for advancing quantum information and photocatalysis technologies.

Electrically programmable magnetic coupling in an Ising network exploiting solid-state ionic gating

Two-dimensional arrays of magnetically coupled nanomagnets provide a mesoscopic platform for exploring collective phenomena as well as realizing a broad range of spintronic devices. In particular, the magnetic coupling plays a critical role in determining the nature of the cooperative behavior and providing new functionalities in nanomagnet-based devices. Here, we create coupled Ising-like nanomagnets in which the coupling between adjacent nanomagnetic regions can be reversibly converted between parallel and antiparallel through solid-state ionic gating. This is achieved with the voltage-control of the magnetic anisotropy in a nanosized region where the symmetric exchange interaction favors parallel alignment and the antisymmetric exchange interaction, namely the Dzyaloshinskii-Moriya interaction, favors antiparallel alignment of the nanomagnet magnetizations. Applying this concept to a two-dimensional lattice, we demonstrate a voltage-controlled phase transition in artificial spin ices. Furthermore, we achieve an addressable control of the individual couplings and realize an electrically programmable Ising network, which opens up new avenues to design nanomagnet-based logic devices and neuromorphic computers.

Graphene Spin Valves for Spin Logic Devices

An alternative to charge-based electronics identifies the spin degree of freedom for information communication and processing. The long spin-diffusion length in graphene at room temperature demonstrates its ability for highly scalable spintronics. The development of the graphene spin valve (SV) has inspired spin devices in graphene including spin field-effect transistors and spin majority logic gates. A comprehensive picture of spin transport in graphene SVs is required for further development of spin logic. This review examines the advances in graphene SVs and their role in the development of spin logic devices. Different transport and scattering mechanisms in charge and spin are discussed. Furthermore, the on/off switching energy between graphene SVs and charge-based FETs is compared to highlight their prospects for low-power devices. The challenges and perspectives that need to be addressed for the future development of spin logic devices are then outlined.

Photonic elementary cellular automata for simulation of complex phenomena

Cellular automata are a class of computational models based on simple rules and algorithms that can simulate a wide range of complex phenomena. However, when using conventional computers, these 'simple' rules are only encapsulated at the level of software. This can be taken one step further by simplifying the underlying physical hardware. Here, we propose and implement a simple photonic hardware platform for simulating complex phenomena based on cellular automata. Using this special-purpose computer, we experimentally demonstrate complex phenomena, including fractals, chaos, and solitons, which are typically associated with much more complex physical systems. The flexibility and programmability of our photonic computer present new opportunities to simulate and harness complexity for efficient, robust, and decentralized information processing using light.

Skyrmion based majority logic gate by voltage controlled magnetic anisotropy in a nanomagnetic device

Magnetic skyrmions are topologically protected spin textures and they are suitable for future logic-in-memory applications for energy-efficient, high-speed information processing and computing technologies. In this work, we have demonstrated skyrmion-based 3 bit majority logic gate using micromagnetic simulations. The skyrmion motion is controlled by introducing agatethat works on voltage controlled magnetic anisotropy. Here, the inhomogeneous magnetic anisotropy behaves as a tunable potential barrier/well that modulates the skyrmion trajectory in the structure for the successful implementation of the majority logic gate. In addition, several other effects such as skyrmion-skyrmion topological repulsion, skyrmion-edge repulsion, spin-orbit torque and skyrmion Hall effect have been shown to govern the logic functionalities. We have systematically presented the robust logic operations by varying the current density, magnetic anisotropy, voltage-controlled gate dimension and geometrical parameters of the logic device. The skyrmion Hall angle is monitored to understand the trajectory and stability of the skyrmion as a function of time in the logic device. The results demonstrate a novel method to achieve majority logic by using voltage controlled magnetic anisotropy which further opens up a new route for skyrmion-based low-power and high-speed computing devices.

Applications of nanomagnets as dynamical systems: I

When magnets are fashioned into nanoscale elements, they exhibit a wide variety of phenomena replete with rich physics and the lure of tantalizing applications. In this topical review, we discuss some of these phenomena, especially those that have come to light recently, and highlight their potential applications. We emphasize what drives a phenomenon, what undergirds the dynamics of the system that exhibits the phenomenon, how the dynamics can be manipulated, and what specific features can be harnessed for technological advances. For the sake of balance, we point out both advantages and shortcomings of nanomagnet based devices and systems predicated on the phenomena we discuss. Where possible, we chart out paths for future investigations that can shed new light on an intriguing phenomenon and/or facilitate both traditional and non-traditional applications.

Interlayer exchange couple based reliable and robust 3-input adder design methodology

In this paper, a novel inter-layer exchange coupled (IEC) based 3-input full adder design methodology is proposed and subsequently the architecture has been implemented on the widely accepted micromagnetic OOMMF platform. The impact of temperature on the IEC coupled full-adder design has been analyzed up to Curie temperature. It was observed that even up to Curie temperature the IEC based adder design was able to operate at sub-50 nm as contrast to dipole coupled adder design which failed at 5 K for sub 50 nm. Simulation results obtained from OOMMF micromagnetic simulator shows, the IEC based adder design was at a lower energy state as compared to the dipole coupled adder indicating a more stable system and as the temperature of the design was increased, the total energy increased resulting in reduced stability. Potential explanation for the thermodynamic stability of IEC model lies in its energetically favored architecture, such that the total energy was lower than its dipole coupled counterparts. IEC architecture demonstrates supremacy in reliability and strength enabling NML to march towards beyond CMOS devices.

Area efficient in-plane nanomagnetic multiplier and convolution architecture design

In this study, we propose a nanomagnetic logic (NML) based 2 bit multiplier architecture design for the first time to the best of author’s knowledge. This complex combinational logic (nanomagnetic multiplier) design proposed is built by exploiting shape, positional hybrid anisotropy and the ferromagnetically coupled fixed input majority gate. Subsequently, we extend this proposed multiplier architecture along with the NML adder architecture in introducing NML based convolution architecture design which is efficient in terms of number of nanomagnets, majority gates and clock-cycles. The proposed NML design yields ∼21%–72%, ∼26%–42%, ∼36%–63%, and ∼20%–68%, reduction in the required number of nanomagnets, majority gate, clock cycles and energy compared to the state-of-the-art designs.

A novel and reliable interlayer exchange coupled nanomagnetic universal logic gate design

In this paper, we propose an interlayer exchange coupling (IEC) based 3D universal NAND/NOR gate design methodology for the reliable and robust implementation of nanomagnetic logic design as compared to the state-of-the art architectures. Owing to stronger coupling scheme as compared to the conventional dipole coupling, the random flip of the states of the nanomagnets (i.e. the soft error) is reduced resulting in greater scalability and better data retention at the deep sub-micron level. Results obtained from Object Oriented Micromagnetic Framework micromagnetic simulation show even at a Curie temperature of the nanomagnets coupled through IEC, the logic function works properly as opposed to dipole coupled nanomagnets which fails at 5 K when scaled down to sub 50 nm. Contemplating the fabrication challenges, the robustness of the IEC design was studied for structural defects, positional misalignment, shape, and size variations. This proposed 3D universal gate design methodology benefits from the miniaturization of nanomagnets as well as reduces the effect of thermally induced errors resulting in opening up a new perspective for nanomagnet based design in magneto-logic devices.

Linear chains of nanomagnets: engineering the effective magnetic anisotropy

This paper investigates the control of effective magnetic anisotropy in Permalloy linear chain arrays, achieved by tuning the symmetry arrangement of the ellipsoidal nanomagnets and the film thickness. When the ellipsoidal nanomagnets are coupled along their easy axis, stronger effective magnetic anisotropy is achieved compared to when the nanomagnets are coupled along their hard axis. A clear transition from a single domain state to a combination of complex flux closure states such as a vortex or double vortices is observed at different applied field angles when the film thickness is varied in the range from 20 nm to 100 nm. Tunable microwave absorption spectra, obtained by ferromagnetic resonance spectroscopy, established the complex interplay between the shape anisotropy and magnetostatic interactions, which becomes more intriguing at different film thicknesses and applied field angles. The micromagnetic simulations are in good agreement with the experimental results. Our results demonstrate possible ways of manipulating the effective magnetic anisotropy in arrays of nanomagnets for magnonic and microwave applications.

Rediscovering Majority Logic in the Post-CMOS Era: A Perspective from In-Memory Computing

As we approach the end of Moore’s law, many alternative devices are being explored to satisfy the performance requirements of modern integrated circuits. At the same time, the movement of data between processing and memory units in contemporary computing systems (‘von Neumann bottleneck’ or ‘memory wall’) necessitates a paradigm shift in the way data is processed. Emerging resistance switching memories (memristors) show promising signs to overcome the ‘memory wall’ by enabling computation in the memory array. Majority logic is a type of Boolean logic which has been found to be an efficient logic primitive due to its expressive power. In this review, the efficiency of majority logic is analyzed from the perspective of in-memory computing. Recently reported methods to implement majority gate in Resistive RAM array are reviewed and compared. Conventional CMOS implementation accommodated heterogeneity of logic gates (NAND, NOR, XOR) while in-memory implementation usually accommodates homogeneity of gates (only IMPLY or only NAND or only MAJORITY). In view of this, memristive logic families which can implement MAJORITY gate and NOT (to make it functionally complete) are to be favored for in-memory computing. One-bit full adders implemented in memory array using different logic primitives are compared and the efficiency of majority-based implementation is underscored. To investigate if the efficiency of majority-based implementation extends to n-bit adders, eight-bit adders implemented in memory array using different logic primitives are compared. Parallel-prefix adders implemented in majority logic can reduce latency of in-memory adders by 50–70% when compared to IMPLY, NAND, NOR and other similar logic primitives.

Local Photothermal Control of Phase Transitions for On-Demand Room-Temperature Rewritable Magnetic Patterning

The ability to make controlled patterns of magnetic structures within a nonmagnetic background is essential for several types of existing and proposed technologies. Such patterns provide the foundation of magnetic memory and logic devices, allow the creation of artificial spin-ice lattices, and enable the study of magnon propagation. Here, a novel approach for magnetic patterning that allows repeated creation and erasure of arbitrary shapes of thin-film ferromagnetic structures is reported. This strategy is enabled by epitaxial Fe_0.52 Rh_0.48 thin films designed so that both ferromagnetic and antiferromagnetic phases are bistable at room temperature. Starting with the film in a uniform antiferromagnetic state, the ability to write arbitrary patterns of the ferromagnetic phase is demonstrated by local heating with a focused laser. If desired, the results can then be erased by cooling below room temperature and the material repeatedly re-patterned.

Nanomagnetic logic based runtime Reconfigurable area efficient and high speed adder design methodology

In this study, we present a runtime reconfigurable nanomagnetic (RRN) adder design offering significant area efficiency and high speed operations. Subsequently, it is implemented using a micromagnetic simulation tool, by exploiting the reversal magnetization and energy minimization nature of the nanomagnets. We compute the carry and sum of the 1-bit full adder using only two majority gates comprising a total of 7 nanomagnets and single design layout. Consequently, the on-chip clocking schematic for the proposed RRN adder implementation for both horizontal and vertical layouts are introduced. The quantitative analysis of the required resources for higher bit adder architecture using the proposed design is performed and compared with state-of-the art. The proposed design methodology leads to ∼86%, ∼83% and ∼93% reduction in the number of nanomagnets, majority gates and clock cycles respectively resulting in an area efficient and high speed RRN adder architecture.

Temperature and Size Effect on the Electrical Properties of Monolayer Graphene based Interconnects for Next Generation MQCA based Nanoelectronics

Graphene interconnects have been projected to out-perform Copper interconnects in the next generation Magnetic Quantum-dot Cellular Automata (MQCA) based nano-electronic applications. In this paper a simple two-step lithography process for patterning CVD monolayer graphene on SiO₂/Si substrate has been used that resulted in the current density of one order higher magnitude as compared to the state-of-the-art graphene-based interconnects. Electrical performances of the fabricated graphene interconnects were evaluated, and the impact of temperature and size on the current density and reliability was investigated. The maximum current density of 1.18 ×10⁸ A/cm² was observed for 0.3 μm graphene interconnect on SiO₂/Si substrate, which is about two orders and one order higher than that of conventionally used copper interconnects and CVD grown graphene respectively, thus demonstrating huge potential in outperforming copper wires for on-chip clocking. The drop in current at 473 K as compared to room temperature was found to be nearly 30%, indicating a positive temperature coefficient of resistivity (TCR). TCR for all cases were studied and it was found that with decrease in width, the sensitivity of temperature also reduces. The effect of resistivity on the breakdown current density was analysed on the experimental data using Matlab and found to follow the power-law equations. The breakdown current density was found to have a reciprocal relationship to graphene interconnect resistivity suggesting Joule heating as the likely mechanism of breakdown.

Dipole coupled magnetic quantum-dot cellular automata-based efficient approximate nanomagnetic subtractor and adder design approach

In this paper, we propose a dipole coupled magnetic quantum-dot cellular automata-based approximate nanomagnetic (APN) architectural design approach for subtractor and adder. In addition, we also introduce an APN architecture which offers runtime reconfigurability using a single design layout comprising only four nanomagnets. Subsequently, we propose the APN add/sub architecture by exploiting shape anisotropy and ferromagnetically coupled fixed input majority gate. The proposed APN architecture designs have been implemented using a micromagnetic simulation tool and performance has been compared with the state-of-the-art approach resulting in a ∼50%-80% reduction in the number of nanomagnets and clock cycles without degradation in the accuracy leading to area and energy efficiency.

Magnetic excitations in assemblies of dipolar coupled nanoparticles

The equilibrium magnetization configurations and the associated microwave susceptibility spectra of dipolar coupled nanoplatelets are explored using three-dimensional (3D) micromagnetic simulations. First, the case of periodic arrangements of nanoplatelets on square arrays is considered. As a result, a macro-vortex state defined as a flux closure pattern spreading over the whole array with or without a vortex core can be stabilized starting from an initial orthoradial magnetization configuration. For macro-vortex states with a vortex core, the linear excitation spectrum exhibits a sub-GHz resonance line ascribed to the vortex core dynamics at the array center. The features of this line (spectral position and amplitude) depend on the array size and the strength of the dipolar coupling through the interplatelet spacing. This resonance is also observed for macro-vortex states without a vortex core but only in the regime of a strong dipolar coupling. The effect of disorder is then investigated by numerically generating assemblies of nanoplatelets with a position disorder and, shape and size distributions. The micromagnetic simulations reveal flux closure magnetization configurations as well but without a vortex core. A low-frequency resonance appears in the susceptibility spectra for quite high surface contents of nanoplatelets but its amplitude is weaker compared to the case of periodic arrays. This line arises from a collective mode extended over a few nanoplatelets.

A large variety of static and dynamical behaviors is thus evidenced resulting in a great complexity even in such model systems.

Magnetization dynamics of weakly interacting sub-100 nm square artificial spin ices

Artificial Spin Ice (ASI), consisting of a two dimensional array of nanoscale magnetic elements, provides a fascinating opportunity to observe the physics of out-of-equilibrium systems. Initial studies concentrated on the static, frozen state, whilst more recent studies have accessed the out-of-equilibrium dynamic, fluctuating state. This opens up exciting possibilities such as the observation of systems exploring their energy landscape through monopole quasiparticle creation, potentially leading to ASI magnetricity, and to directly observe unconventional phase transitions. In this work we have measured and analysed the magnetic relaxation of thermally active ASI systems by means of SQUID magnetometry. We have investigated the effect of the interaction strength on the magnetization dynamics at different temperatures in the range where the nanomagnets are thermally active. We have observed that they follow an Arrhenius-type Néel-Brown behaviour. An unexpected negative correlation of the average blocking temperature with the interaction strength is also observed, which is supported by Monte Carlo simulations. The magnetization relaxation measurements show faster relaxation for more strongly coupled nanoelements with similar dimensions. The analysis of the stretching exponents obtained from the measurements suggest 1-D chain-like magnetization dynamics. This indicates that the nature of the interactions between nanoelements lowers the dimensionality of the ASI from 2-D to 1-D. Finally, we present a way to quantify the effective interaction energy of a square ASI system, and compare it to the interaction energy computed with micromagnetic simulations.

Voltage-induced strain clocking of nanomagnets with perpendicular magnetic anisotropies

Nanomagnetic logic (NML) has attracted attention during the last two decades due to its promise of high energy efficiency combined with non-volatility. Data transmission in NML relies on Bennett clocking through dipole interaction between neighboring nanomagnetic bits. This paper uses a fully coupled finite element model to simulate Bennett clocking based on strain-mediated multiferroic system for Ni, CoFeB and Terfenol-D with perpendicular magnetic anisotropies. Simulation results demonstrate that Terfenol-D system has the highest energy efficiency, which is 2 orders of magnitude more efficient than Ni and CoFeB. However, the high efficiency is associated with switching incoherency due to its large magnetostriction coefficient. It is also suggested that the CoFeB clocking system has lower bit-density than in Ni or Terfenol-D systems due to its large dipole coupling. Moreover, we demonstrate that the precessional perpendicular switching and the Bennett clocking can be achieved using the same strain-mediated multiferroic architecture with different voltage pulsing. This study opens new possibilities to an all-spin in-memory computing system.

Three-dimensional frequency- and phase-multiplexed magneto-optical microscopy

We describe a new approach to scanning magneto-optical Kerr effect (MOKE) microscopy in which two opto-mechanical choppers modulate the spatial profile of a probe laser beam to separately encode all three magnetization components at different frequencies and phases in one signal. We demonstrate this multiplexed technique in two representative regimes: the equilibrium and non-equilibrium response of a magnetic vortex to a changing magnetic field. We observe the translation of the vortex state in equilibrium and the spiraling gyrotropic trajectory of the vortex position out of equilibrium. We compare the results to a traditional MOKE measurement and to micromagnetic simulations. We find that the multiplexed method presented here provides better agreement with simulation than previous methods and equal or better signal-to-noise ratio.

Nanomagnetic logic design approach for area and speed efficient adder using ferromagnetically coupled fixed input majority gate

In this letter, we introduce the magnetic quantum-dot cellular automata (MQCA) based area and speed efficient design approach for nanomagnetic full adder implementation. We exploited the physical properties of three input MQCA majority gate (MG), where the fixed input of the MG is coupled ferromagnetically to one of the primary input operands. Subsequently we propose a design methodology, mapping logic and micromagnetic software implementation, validation of the binary full adder architecture built using two-three inputs MQCA MGs. In addition, we also analyzed our proposed design for switching errors to ensure bit stability and reliability. Our proposed design leads to ∼36%-69% reduction in the number of nanomagnets, ∼50%-75% reduction in the number of clock cycles and ∼33%-50% reduction in the number of MG operations required for the binary full adder implementation compared to the state of art designs.

Implementing Functionality in Molecular Self-Assembled Monolayers

The planar heterocyclic molecules 1,6,7,12-tetraazaperylene on a Ag(111) metal substrate show different charging characteristics depending on their local environment: next to vacancies in self-assembled islands, molecules can be charged by local electric fields, whereas their charge state is fixed otherwise. This enables the activation of selected molecules inside islands by vacancy creation from scanning-probe-based manipulation. This concept allows for combining the precise mutual atomic-scale alignment of molecules by self-assembly, on one hand, and the implementation of specific functionality into otherwise homogeneous monolayers, on the other. Activated molecules in the direct neighborhood influence each other in their charging characteristics, suggesting their use as molecular quantum cellular automata. Surprisingly, only very few interacting molecules exhibit a rich spectroscopic signature, which offers the prospect of implementing complex functionality in such structures in the future.

Selective and fast plasmon-assisted photo-heating of nanomagnets

Thermal relaxation of nanoscale magnetic islands, mimicking Ising macrospins, is indispensable for studies of geometrically frustrated artificial spin systems and low-energy nanomagnetic computation. Currently-used heating schemes based on contact to a thermal reservoir, however, lack the speed and spatial selectivity required for the implementation in technological applications. Applying a hybrid approach by combining a plasmonic nanoheater with a magnetic element, in this work we establish the robust and reliable control of local temperatures in nanomagnetic arrays by contactless optical means. Plasmon-assisted photo-heating allows for temperature increases of up to several hundred kelvins, which lead to thermally-activated moment reversals and a pronounced reduction of the magnetic coercive field. Furthermore, the polarization-dependent absorption cross section of elongated plasmonic elements enables sublattice-specific heating on sub-nanosecond time scales. Using optical degrees of freedom, i.e. focal position, polarization, power, and pulse length, thermoplasmonic heating of nanomagnets offers itself for the use in flexible, fast, spatially-, and element-selective thermalization for functional magnetic metamaterials.

Chirally coupled nanomagnets

Magnetically coupled nanomagnets have multiple applications in nonvolatile memories, logic gates, and sensors. The most effective couplings have been found to occur between the magnetic layers in a vertical stack. We achieved strong coupling of laterally adjacent nanomagnets using the interfacial Dzyaloshinskii-Moriya interaction. This coupling is mediated by chiral domain walls between out-of-plane and in-plane magnetic regions and dominates the behavior of nanomagnets below a critical size. We used this concept to realize lateral exchange bias, field-free current-induced switching between multistate magnetic configurations as well as synthetic antiferromagnets, skyrmions, and artificial spin ices covering a broad range of length scales and topologies. Our work provides a platform to design arrays of correlated nanomagnets and to achieve all-electric control of planar logic gates and memory devices.

Scalable energy-efficient magnetoelectric spin-orbit logic

Since the early 1980s, most electronics have relied on the use of complementary metal-oxide-semiconductor (CMOS) transistors. However, the principles of CMOS operation, involving a switchable semiconductor conductance controlled by an insulating gate, have remained largely unchanged, even as transistors are miniaturized to sizes of 10 nanometres. We investigated what dimensionally scalable logic technology beyond CMOS could provide improvements in efficiency and performance for von Neumann architectures and enable growth in emerging computing such as artifical intelligence. Such a computing technology needs to allow progressive miniaturization, reduce switching energy, improve device interconnection and provide a complete logic and memory family. Here we propose a scalable spintronic logic device that operates via spin-orbit transduction (the coupling of an electron's angular momentum with its linear momentum) combined with magnetoelectric switching. The device uses advanced quantum materials, especially correlated oxides and topological states of matter, for collective switching and detection. We describe progress in magnetoelectric switching and spin-orbit detection of state, and show that in comparison with CMOS technology our device has superior switching energy (by a factor of 10 to 30), lower switching voltage (by a factor of 5) and enhanced logic density (by a factor of 5). In addition, its non-volatility enables ultralow standby power, which is critical to modern computing. The properties of our device indicate that the proposed technology could enable the development of multi-generational computing.

Energy-efficient switching of nanomagnets for computing: straintronics and other methodologies

The need for increasingly powerful computing hardware has spawned many ideas stipulating, primarily, the replacement of traditional transistors with alternate 'switches' that dissipate miniscule amounts of energy when they switch and provide additional functionality that are beneficial for information processing. An interesting idea that has emerged recently is the notion of using two-phase (piezoelectric/magnetostrictive) multiferroic nanomagnets with bistable (or multi-stable) magnetization states to encode digital information (bits), and switching the magnetization between these states with small voltages (that strain the nanomagnets) to carry out digital information processing. The switching delay is ∼1 ns and the energy dissipated in the switching operation can be few to tens of aJ, which is comparable to, or smaller than, the energy dissipated in switching a modern-day transistor. Unlike a transistor, a nanomagnet is 'non-volatile', so a nanomagnetic processing unit can store the result of a computation locally without refresh cycles, thereby allowing it to double as both logic and memory. These dual-role elements promise new, robust, energy-efficient, high-speed computing and signal processing architectures (usually non-Boolean and often non-von-Neumann) that can be more powerful, architecturally superior (fewer circuit elements needed to implement a given function) and sometimes faster than their traditional transistor-based counterparts. This topical review covers the important advances in computing and information processing with nanomagnets, with emphasis on strain-switched multiferroic nanomagnets acting as non-volatile and energy-efficient switches-a field known as 'straintronics'. It also outlines key challenges in straintronics.

Quantum Artificial Life in an IBM Quantum Computer

We present the first experimental realization of a quantum artificial life algorithm in a quantum computer. The quantum biomimetic protocol encodes tailored quantum behaviors belonging to living systems, namely, self-replication, mutation, interaction between individuals, and death, into the cloud quantum computer IBM ibmqx4. In this experiment, entanglement spreads throughout generations of individuals, where genuine quantum information features are inherited through genealogical networks. As a pioneering proof-of-principle, experimental data fits the ideal model with accuracy. Thereafter, these and other models of quantum artificial life, for which no classical device may predict its quantum supremacy evolution, can be further explored in novel generations of quantum computers. Quantum biomimetics, quantum machine learning, and quantum artificial intelligence will move forward hand in hand through more elaborate levels of quantum complexity.

A majority gate with chiral magnetic solitons

In magnetic materials, nontrivial spin textures may emerge due to the competition among different types of magnetic interactions. Among such spin textures, chiral magnetic solitons represent topologically protected spin configurations with particle-like properties. Based on atomistic spin dynamics simulations, we demonstrate that these chiral magnetic solitons are ideal to use for logical operations, and we demonstrate the functionality of a three-input majority gate, in which the input states can be controlled by applying an external electromagnetic field or spin-polarized currents. One of the main advantages of the proposed device is that the input and output signals are encoded in the chirality of solitons, that may be moved, allowing to perform logical operations using only minute electric currents. As an example we illustrate how the three input majority gate can be used to perform logical relations, such as Boolean AND and OR.

Ising-like behaviour of mesoscopic magnetic chains

We demonstrate an experimental realization of the short range magnetic order in a one-dimensional Ising chain using fabricated mesospins. We confirm an excellent agreement between the experimental findings and simulations obtained using the original Ising model. In particular, we are able to show that the thermal behaviour of the mesoscopic Ising chain dominates over the thermal behaviour of the individual mesospins themselves, confirming that fabricated mesospins can be viewed as artificial magnetic atoms.

Crystalline and magnetic structure-property relationship in spinel ferrite nanoparticles

Magnetic spinel ferrite MFe2O4 (M = Mn, Co, Ni, Zn) nanoparticles have been prepared via simple, green and scalable hydrothermal synthesis pathways utilizing sub- and supercritical conditions to attain specific product characteristics. The crystal-, magnetic- and micro-structures of the prepared crystallites have been elucidated through meticulous characterization employing several complementary techniques. Analysis of energy dispersive X-ray spectroscopy (EDS) and X-ray absorption near edge structure (XANES) data verifies the desired stoichiometries with divalent M and trivalent Fe ions. Robust structural characterization is carried out by simultaneous Rietveld refinement of a constrained structural model to powder X-ray diffraction (PXRD) and high-resolution neutron powder diffraction (NPD) data. The structural modeling reveals different affinities of the 3d transition metal ions for the specific crystallographic sites in the nanocrystallites, characterized by the spinel inversion degree, x, [M2+1-xFe3+x]tet[M2+xFe3+2-x]octO4, compared to the well-established bulk structures. The MnFe2O4 and CoFe2O4 nanocrystallites exhibit random disordered spinel structures (x = 0.643(3) and 0.660(6)), while NiFe2O4 is a completely inverse spinel (x = 1.00) and ZnFe2O4 is close to a normal spinel (x = 0.166(10)). Furthermore, the size, size distribution and morphology of the nanoparticles have been assessed by peak profile analysis of the diffraction data, transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The differences in nanostructure, spinel inversion and distinct magnetic nature of the M2+ ions directly alter the magnetic structures of the crystallites at the atomic-scale and consequently the macroscopic magnetic properties of the materials. The present study serves as an important structural benchmark for the rapidly expanding field of spinel ferrite nanoparticle research.

Computational logic with square rings of nanomagnets

Nanomagnets are a promising low-power alternative to traditional computing. However, the successful implementation of nanomagnets in logic gates has been hindered so far by a lack of reliability. Here, we present a novel design with dipolar-coupled nanomagnets arranged on a square lattice to (i) support transfer of information and (ii) perform logic operations. We introduce a thermal protocol, using thermally active nanomagnets as a means to perform computation. Within this scheme, the nanomagnets are initialized by a global magnetic field and thermally relax on raising the temperature with a resistive heater. We demonstrate error-free transfer of information in chains of up to 19 square rings and we show a high level of reliability with successful gate operations of ∼94% across more than 2000 logic gates. Finally, we present a functionally complete prototype NAND/NOR logic gate that could be implemented for advanced logic operations. Here we support our experiments with simulations of the thermally averaged output and determine the optimal gate parameters. Our approach provides a new pathway to a long standing problem concerning reliability in the use of nanomagnets for computation.

Studies on a multifunctional chromo-fluorogenic sensor for dual channel recognition of Zn2+ and CN− ions in aqueous media: mimicking multiple molecular logic gates and memory devices

A new effectual naphthalene-based azomethine receptor has been systematically designed and synthesized as a selective colorimetric and fluorescent chemosensor for dual channel detection of cations and anions in aqueous environments.

Implementation of cascade logic gates and majority logic gate on a simple and universal molecular platform

Wiring a series of simple logic gates to process complex data is significantly important and a large challenge for untraditional molecular computing systems. The programmable property of DNA endows its powerful application in molecular computing. In our investigation, it was found that DNA exhibits excellent peroxidase-like activity in a colorimetric system of TMB/H₂O₂/Hemin (TMB, 3,3′, 5,5′-Tetramethylbenzidine) in the presence of K⁺ and Cu²⁺, which is significantly inhibited by the addition of an antioxidant. According to the modulated catalytic activity of this DNA-based catalyst, three cascade logic gates including AND-OR-INH (INHIBIT), AND-INH and OR-INH were successfully constructed. Interestingly, by only modulating the concentration of Cu²⁺, a majority logic gate with a single-vote veto function was realized following the same threshold value as that of the cascade logic gates. The strategy is quite straightforward and versatile and provides an instructive method for constructing multiple logic gates on a simple platform to implement complex molecular computing.

Realization of tunable artificial synapse and memory based on amorphous oxide semiconductor transistor

Recently, advanced designs and materials emerge to study biologically inspired neuromorphic circuit, such as oxide semiconductor devices. The existence of mobile ions in the oxide semiconductors could be somewhat regarded to be similar with the case of the ions movements among the neurons and synapses in the brain. Most of the previous studies focus on the spike time, pulse number and material species: however, a quantitative modeling is still needed to study the voltage dependence of the relaxation process of synaptic devices. Here, the gate pulse stimulated currents of oxide semiconductor devices have been employed to mimic and investigate artificial synapses functions. The modeling for relaxation process of important synaptic behaviors, excitatory post-synaptic current (EPSC), has been updated as a stretched-exponential function with voltage factors in a more quantitative way. This quantitative modeling investigation of representative synaptic transmission bias impacts would help to better simulate, realize and thus control neuromorphic computing.

Nanoscale magnetic ratchets based on shape anisotropy

Controlling magnetization using piezoelectric strain through the magnetoelectric effect offers several orders of magnitude reduction in energy consumption for spintronic applications. However strain is a uniaxial effect and, unlike directional magnetic field or spin-polarized current, cannot induce a full 180° reorientation of the magnetization vector when acting alone. We have engineered novel 'peanut' and 'cat-eye' shaped nanomagnets on piezoelectric substrates that undergo repeated deterministic 180° magnetization rotations in response to individual electric-field-induced strain pulses by breaking the uniaxial symmetry using shape anisotropy. This behavior can be likened to a magnetic ratchet, advancing magnetization clockwise with each piezostrain trigger. The results were validated using micromagnetics implemented in a multiphysics finite elements code to simulate the engineered spatial and temporal magnetic behavior. The engineering principles start from a target device function and proceed to the identification of shapes that produce the desired function. This approach opens a broad design space for next generation magnetoelectric spintronic devices.

Intra-wire coupling in segmented Ni/Cu nanowires deposited by electrodeposition

Segmented magnetic nanowires are a promising route for the development of three dimensional data storage techniques. Such devices require a control of the coercive field and the coupling mechanisms between individual magnetic elements. In our study, we investigate electrodeposited nanomagnets within host templates using vibrating sample magnetometry and observe a strong dependence between nanowire length and coercive field (25 nm-5 μm) and diameter (25-45 nm). A transition from a magnetization reversal through coherent rotation to domain wall propagation is observed at an aspect ratio of approximately 2. Our results are further reinforced via micromagnetic simulations and angle dependent hysteresis loops. The found behavior is exploited to create nanowires consisting of a fixed and a free segment in a spin-valve like structure. The wires are released from the membrane and electrically contacted, displaying a giant magnetoresistance effect that is attributed to individual switching of the coupled nanomagnets. We develop a simple analytical model to describe the observed switching phenomena and to predict stable and unstable regimes in coupled nanomagnets of certain geometries.

Exchange coupling between laterally adjacent nanomagnets

We experimentally demonstrate exchange-coupling between laterally adjacent nanomagnets. Our results show that two neighboring nanomagnets that are each antiferromagnetically exchange-coupled to a common ferromagnetic bottom layer can be brought into strong ferromagnetic interaction. Simulations show that interlayer exchange coupling effectively promotes ferromagnetic alignment between the two nanomagnets, as opposed to antiferromagnetic alignment due to dipole-coupling. In order to experimentally demonstrate the proposed scheme, we fabricated arrays of pairs of elongated, single-domain nanomagnets. Magnetic force microscopy measurements show that most of the pairs are ferromagnetically ordered. The results are in agreement with micromagnetic simulations. The presented scheme can achieve coupling strengths that are significantly stronger than dipole coupling, potentially enabling far-reaching applications in Nanomagnet Logic, spin-wave devices and three-dimensional storage and computing.