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In this work, we have studied the spin dynamics of a synthetic antiferromagnet (AFM)/heavy metal/ferromagnet double barrier magnetic tunnel junction in the presence of Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction, interfacial Dzyaloshinskii–Moriya (iDM) interaction, Néel field, and Spin–Orbit Coupling (SOC) with different Spin-Transfer Torque (STT). We employ the Landau–Lifshitz–Gilbert–Slonczewski equation to investigate the AFM dynamics of the proposed system. We found that the system exhibits a transition from regular to damped oscillations with the increase in strength of STT for systems with a weaker strength of iDM interaction than RKKY interaction while displaying sustained oscillations for systems having the same order of RKKY and iDM interactions. On the other hand, the systems with sufficiently strong iDM interaction strength exhibit self-similar but aperiodic patterns in the absence of the Néel field. In the presence of the Néel field, the RKKY interaction dominating systems exhibit chaotic oscillations for low STT but display sustained oscillations under moderate STT. Our results suggest that the decay time of oscillations can be controlled via SOC. The system can work as an oscillator for low SOC but displays non-linear characteristics with the rise in SOC for systems having weaker iDM interaction than RKKY interactions. In contrast, opposite characteristics are noticed for iDM interaction dominating systems. We found periodic oscillations under low external magnetic fields in RKKY interaction dominating systems. However, moderate fields are necessary for sustained oscillation in iDM interaction dominating systems. Moreover, the system exhibits saddle-node bifurcations and chaos under moderate Néel field and SOC with suitable RKKY and iDM interactions. In addition, our results indicate that the magnon lifetime can be enhanced by increasing the strength of iDM interaction for both optical and acoustic modes. [ABSTRACT FROM AUTHOR]

This article analytically explores defect assisted spin injection in organic magnetic tunnel junctions (MTJs) [x/rubrene/Co, x = La 2 O 3 , LaMnO 3 , La 0.7 Ca 0.3 MnO 3 (LCMO), La 0.7 Sr 0.3 MnO 3 (LSMO)] employing nonequilibrium Green's function (NEGF). Spin precession at ferromagnet (FM)/organic semiconductor (OSC) interface defect states have been considered while modeling the MTJ devices. Variations in voltage dependent parallel (R P) and antiparallel (R A P ) resistances have been attributed to modified spin dependent scattering at modified spin resolved density of states of magnetic electrodes. Moreover, change in distribution of defect state depths at a spin injection interface has also been observed to modify R P /R A P , and hence, tunnel magnetoresistance (TMR) across the devices. Localization of defect state distribution due to a high spin split band may have resulted in large TMR for La 2 O 3 devices. Nonlinear spin transfer torque (STT) in devices other than LSMO indicates compensation of spin damping, resulting in a high TMR response across the devices. Hence, the localization of defect state distribution and the choice of magnetic electrodes with high spin split bands may be exercised to realize spintronic devices for low power spin memory applications. [ABSTRACT FROM AUTHOR]

The urgent demand for high-performance emerging memory, propelled by artificial intelligence in internet of things (AIoT) and machine learning advancements, spotlights spin-transfer torque magnetic random-access memory as a prime candidate for practical application. However, magnetic tunnel junctions (MTJs) with a single-crystalline MgO barrier, which are central to magnetic random-access memory (MRAM), suffer from significant drawbacks: insufficient endurance due to breakdown and high writing power requirements. A superlattice barrier-based MTJ (SL-MTJ) is proposed to overcome the limitation. We first fabricated the MTJ using an SL barrier while examining the magnetoresistance and resistance-area product. Lower writing power can be achieved in SL-MTJs compared to MgO-MTJs. Our study may provide a new route to the development of MRAM technologies. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new approach for constructing broadband rectifiers from resonant-type in-plane spin-torque diodes (STDs). The intrinsic bandwidth of such STDs constrained by the ferromagnetic resonance linewidth of the corresponding magnetic tunnel junction's is relatively narrow, which is a significant limitation. To address this issue, we propose the implementation of an array of these STDs, each with a distinct resonance frequency. By ensuring that the frequency difference between adjacent STDs is smaller than their individual bandwidths, we achieve a device capable of rectifying signals over a much wider frequency range. To verify the effectiveness of our approach, we have performed analytical calculations based on the Landau–Lifshitz–Gilbert equation with the Slonczewski term, complemented by macrospin modeling and full-scale micromagnetic simulations to account for thermal fluctuations and local magnetization inhomogeneities. Our results demonstrate that an STD array can effectively function as a broadband energy harvester, maintaining near-constant rectification efficiency across a broad frequency range. This research establishes the groundwork for the development of broadband energy harvesters based on STD arrays, with potential applications in various fields requiring efficient energy conversion across a wide frequency spectrum. [ABSTRACT FROM AUTHOR]

In magnetic tunnel junctions (MTJs), an antiferromagnetic iridium manganese (IrMn) layer neighboring a ferromagnetic electrode is indispensable for pinning the magnetization of the ferromagnet. The effect of its antiferromagnetism on adjacent ferromagnet and, thus, the quantum transport is, nevertheless, scarcely studied. Here, we investigate the role of antiferromagnetically orientated Mn spins in IrMn on the spin-dependent tunneling transport in IrMn/FeCo/MgO/FeCo/IrMn MTJ by analyzing the tunneling magnetoresistance (TMR) effect. The opposite spin orientation of Mn induces the mixing of Bloch symmetries, Δ 1 and Δ 5 , irrespective of the spin alignment of the FeCo electrode. This auxiliary contribution from the Mn spins improves the tunneling in majority- and minority-spin channels in parallel configuration. In the antiparallel configuration, the tunneling in majority- and minority-spin channels is non-identical. The TMR as high as 8643% is obtained under equilibrium. In addition, the non-equilibrium behavior of TMR and the spin-filtering effect are examined in the voltage bias range of 10–50 mV. The TMR ratio of 3600% with the spin-filtering efficiency of ∼ 98% is maintained at 50 mV, presenting the MTJ as an effective spin-filtering device robust to the bias endurance. Finally, it is speculated that our device structure can be a potential spin–orbit torque-based MTJ that offers a giant TMR and promotes upscaling of the generation of multi-bit devices with a simplified design strategy. [ABSTRACT FROM AUTHOR]

While magnetoresistive random-access memory (MRAM) stands out as a leading candidate for embedded nonvolatile memory and last-level cache applications, its endurance is compromised by substantial self-heating due to the high programming current density. The effect of self-heating on the endurance of the magnetic tunnel junction (MTJ) has primarily been studied in spin-transfer torque (STT)-MRAM. Here, we analyze the transient temperature response of two-terminal spin–orbit torque (SOT)-MRAM with a 1 ns switching current pulse using electro-thermal simulations. We estimate a peak temperature range of 350–450 °C in 40 nm diameter MTJs, underscoring the critical need for thermal management to improve endurance. We suggest several thermal engineering strategies to reduce the peak temperature by up to 120 °C in such devices, which could improve their endurance by at least a factor of 1000× at 0.75 V operating voltage. These results suggest that two-terminal SOT-MRAM could significantly outperform conventional STT-MRAM in terms of endurance, substantially benefiting from thermal engineering. These insights are pivotal for thermal optimization strategies in the development of MRAM technologies. [ABSTRACT FROM AUTHOR]

Writing and reading of magnetization states via mechanical strain are crucial for the development of ultralow-power spintronic devices. In this study, a van der Waals magnetic tunnel junction (vdW MTJ) of Fe3GaTe2/h-BN/MnBi2Te4 is constructed to explore the magnetization reversal under in-plane biaxial strains. Interestingly, the interlayer magnetic coupling of devices can be tuned to ferromagnetic and antiferromagnetic states by tensile and compressive strains, respectively. The various magnetic couplings on applied strains are analyzed using the superexchange theory. Importantly, the interlayer coupling nearly vanishes after removing external strains, ensuring the nonvolatility of magnetization reversal, resulting in the nonvolatile writing of magnetization states in the present vdW MTJ. Moreover, the tunneling magnetoresistance ratio of the device is up to −5745%, which remains −1478% even with −2% strain, showing great potential for reading the magnetization states. Therefore, this work provides an alternate avenue to write and read magnetization states in one vdW MTJ under biaxial strains. [ABSTRACT FROM AUTHOR]

Atomic-scale spectroscopic imaging of sputtered magnetic tunnel junction structures with a thick oxygen-rich MgO barrier reveals the diffusion of iron and cobalt into the MgO barrier from CoFeB electrodes. First principles calculations are performed to (1) confirm that Fe diffusion through Mg vacancies is energetically favorable, (2) quantify the reduction of interfacial perpendicular magnetic anisotropy due to Fe diffusion into MgO, and (3) predict that the presence of Fe impurities in MgO causes an increased leakage and a tunneling magnetoresistance decrease. Through the chemical shift of the Fe L3 edge and the peak ratio Fe L3/Fe L2 measured by electron energy loss spectroscopy, we suggest that, within MgO, iron with mixed oxidation state Fe2+ and Fe3+ or higher is found in the as-grown structure, which is reduced by annealing to Fe2+. These results indicate that the stoichiometry of as-deposited MgO barrier layers plays an important role in controlling the microstructure and optimizing the performance of magnetic tunnel junctions. [ABSTRACT FROM AUTHOR]

In our previous work, we synthesized a metal/2D material heterointerface consisting of L 1 0 -ordered iron–palladium (FePd) and graphene (Gr) called FePd(001)/Gr. This system has been explored by both experimental measurements and theoretical calculations. In this study, we focus on a heterojunction composed of FePd and multilayer graphene referred to as FePd(001)/ m -Gr/FePd(001), where m represents the number of graphene layers. We perform first-principles calculations to predict their spin-dependent transport properties. The quantitative calculations of spin-resolved conductance and magnetoresistance (MR) ratio (150 %– 200 %) suggest that the proposed structure can function as a magnetic tunnel junction in spintronics applications. We also find that an increase in m not only reduces conductance but also changes transport properties from the tunneling behavior to the graphite π -band-like behavior. Additionally, we investigate the spin-transfer torque-induced magnetization switching behavior of our junction structures using micromagnetic simulations. Furthermore, we examine the impact of lateral displacements (sliding) at the interface and find that the spin transport properties remain robust despite these changes; this is the advantage of two-dimensional material hetero-interfaces over traditional insulating barrier layers such as MgO. [ABSTRACT FROM AUTHOR]

Heusler alloy-based magnetic tunnel junctions have the potential to provide high spin polarization, small damping, and fast switching. In this study, junctions with a ferromagnetic electrode of Co2FeAl were fabricated via room-temperature sputtering on Si/SiO2 substrates. The effect of boron doping on Co2FeAl magnetic tunnel junctions was investigated for different boron concentrations. The surface roughness determined by atomic force microscope, and the analysis of x-ray diffraction measurement on the Co2FeAl thin film reveals critical information about the interface. The Co2FeAl layer was deposited on the bottom and on the top of the insulating MgO layer as two different sample structures to compare the impact of the boron doping on different layers through tunneling magnetoresistance measurements. The doping of boron in Co2FeAl had a large positive impact on the structural and magneto-transport properties of the junctions, with reduced interfacial roughness and substantial improvement in tunneling magnetoresistance. In samples annealed at low temperature, a two-level magnetoresistance was also observed. This is believed to be related to the memristive effect of the tunnel barrier. The findings of this study have practical uses for the design and fabrication of magnetic tunnel junctions with improved magneto-transport properties. [ABSTRACT FROM AUTHOR]

Memristors and magnetic tunnel junctions are showing great potential in data storage and computing applications. A magnetoelectrically coupled memristor utilizing electron spin and electric field‐induced ion migration can facilitate their operation, uncover new phenomena, and expand applications. In this study, devices consisting of Pt/(LaCoO3/SrTiO3)n/LaCoO3/Nb:SrTiO3 (Pt/(LCO/STO)n/LCO/NSTO) are engineered using pulsed laser deposition to form the LCO/STO superlattice layer, with Pt and NSTO serving as the top and bottom electrodes, respectively. The results show that both memristive and magnetoresistive properties can coexist without any compromise in performance, and the values of ROFF/RON and tunnel magnetoresistance (TMR) ratio are both improved by ≈1000% compared to a single‐period heterostructure. Notably, the Pt/(LCO/STO)5/LCO/NSTO device demonstrates superior multilevel storage performance, characterized by extended endurance, reliable retention, high ROFF/RON ratio, significant TMR ratio, and fundamental synaptic behaviors. Furthermore, density functional theory (DFT) is employed to calculate the changes in oxygen vacancies, affecting the overall energy bands and magnetic moments in the monolayer and multi‐periodic structures. Simulations using the handwritten digit recognition classification achieve the highest accuracy of 94.38%. These attributes suggest that the devices hold considerable promise for application in data storage and neuromorphic computing, offering a platform for high‐density neural circuits in intelligent electronic devices. [ABSTRACT FROM AUTHOR]

Probabilistic computing (p‐computing) is a customized approach for solving complex combinatorial optimization problems. However, issues of compatibility with well‐established complementary metal‐oxide‐semiconductor (CMOS) technology, robustness to environmental temperature variations and stochasticity need to be addressed. This study resolves these difficulties using a metal‐oxide‐semiconductor field‐effect transistor (MOSFET) with a floating body as a probabilistic‐bit (p‐bit) device. Unlike previously reported two‐terminal p‐bit structures, such as magnetic tunnel junction (MTJ) and memristor‐based devices, a MOSFET is commercialized for conventional von Neumann computing. Although MOSFET operation is sensitive to the ambient temperature, a homeothermic characteristic from 20 °C up to 110 °C is achieved with gate voltage (VG) control, taking advantage of the three‐terminal design. The conventional MOSFET operation is stable, reproducible, and, thus, non‐stochastic. However, the floating body effect in this specific MOSFET enhances stochasticity, enabling an irregular single transistor latch (STL). Invertible logic operations and a max‐cut solver are demonstrated with the proposed p‐bits, maintaining desirable performance even at 110 °C through VG control. Due to its compatibility with CMOS technology, large‐scale cointegration of a p‐bit array and supportive CMOS circuits is feasible. [ABSTRACT FROM AUTHOR]

Neuromorphic computing, inspired by biological nervous systems, is gaining traction due to its advantages in latency, energy efficiency, and algorithmic complexity compared to traditional artificial neural networks. This has spurred research into artificial synapses and neurons that replicate brain functions. Spintronic-based technologies, particularly domain walls (DWs) and skyrmions (SKs), have shown remarkable potential for brain-inspired computing, facilitating energy-efficient data storage and advancing beyond CMOS computing architectures. Researchers have proposed various DWs- and Sks-based neuromorphic architectures for neurons and synapses. Leveraging magnetic multilayer structures, we propose a magnetic soliton that incorporates both DWs- and Sks-based magnetic tunnel junction (MTJ) device structures to emulate leaky integrate-and-fire (LIF) characteristics. These characteristics are controlled by spin–orbit torque (SOT)-driven motion within ferromagnetic thin films. By strategically placing the reading block and utilizing a combination of SOT and varying demagnetization energy, we achieve modified LIF neuron characteristics in both DW and Sks MTJ devices. The co-action of soliton dynamics across the nanotrack during the application of the current pulse, along with edge repulsion and variations in demagnetization energy, exploits LIF spiking behavior. Theoretical and micromagnetic analyses reveal that the transitory tunable positions of Sks and the total magnetization of the free layer for DWs mimic the membrane potential of biological neurons. Initial studies on multilayer DW-based LIF characteristics showed promise; however, maintaining leaky behavior required a constant negative current, which is energy inefficient. By incorporating the non-volatile properties of skyrmions and adding a chiral Dzyaloshinskii–Moriya interaction term, we further explored LIF dynamics, yielding encouraging results. Our proposed neuron model, implemented in fully connected and convolutional layers, achieves over 95% classification accuracy on the MNIST and Fashion MNIST datasets using a modified spike-based backpropagation method. With nanosecond latency, these spiking neuron devices, when integrated with CMOS, pave the way for high-density, energy-efficient neuromorphic computing hardware. [ABSTRACT FROM AUTHOR]

The manipulation of the electron spin direction at very low electron energies is demonstrated by exploiting the exchange field present within a magnetic thin film. The design of the lab‐on‐chip integrated magnetic tunnel transistor allows to test different magnetic materials. The variation of film thickness, exchange field strength or electron energy are shown to have an impact on the resulting spin direction of electrons crossing a ferromagnetic material. A controlled engineering of the exchange field in thin magnetic films can therefore serve as a basis of future devices enabling controlled spin manipulation. [ABSTRACT FROM AUTHOR]

We present a simple model of composite particle tunnelling through a potential barrier in presence of a (pseudo)magnetic field. The exact numerical solution of the problem is provided and the applicability to real physical systems is discussed. When the magnetic field is present some new qualitative features of the transmission spectrum are observed, compared to the previously studied composite particle tunnelling with no magnetic field. Splitting of energy levels in a magnetic field leads to splitting of transmission probability resonances, which are a generic feature of composite particle tunnelling. Magnetic field also induces precession of spin on the Bloch sphere, that can be used as a Larmor clock for measuring tunnelling time. [ABSTRACT FROM AUTHOR]

Metallization, plasma, and thermal annealing used in magneto-resistive random access memory integration differs significantly from traditional interconnection processes, usually resulting in the device performance deterioration of metal-oxide-silicon field-effect transistors. Commonly used methods, such as hydrogen postalloying, may not be effective to recover performance when magneto-resistive random access memory is integrated. The study focused on the interplay between hydrogen content in the dielectric films, wafer configuration induced by film stress, and thermal annealing during the chip fabrication process. Post-thermal annealing can enhance the release of hydrogen from the dielectric films, which can repair the silicon–hydrogen bond breakage resulting from magneto-resistive random access memory integration. However, this process can also worsen wafer bowing in an undesired direction which is detrimental to the performance of metal-oxide-silicon field-effect transistors. Consequently, utilizing silicon nitride with specific hydrogen content, in conjunction with post-thermal annealing, can improve effectively both p-type and n-type metal-oxide-silicon field-effect transistors. This approach holds significant potential for application in more advanced technological nodes since it is compatible with traditional process and does not require more advanced fabrication equipment. Additionally, the resulting embedded magneto-resistive random access memory chips maintain competitive magnetic tunneling junction reliability in term of endurance and reflow resistivity. [ABSTRACT FROM AUTHOR]

This study offers a comprehensive investigation into the fabrication of all-oxide-based magnetic tunnel junctions (MTJs) utilizing the focused ion beam (FIB) nanomachining method. The oxide thin films of SrTiO3 (STO), La 1 − x CaxMnO3 (LCMO) and La 1 − x SrxMnO3 (LSMO) were grown using pulsed laser deposition (PLD). Magnetization measurements at 5K revealed a notable difference in coercivity between LCMO and LSMO films, highlighting their suitability as electrodes in MTJ device fabrication. The deposited trilayer structure of LCMO/STO/LSMO exhibited heteroepitaxial growth, enabling the independent magnetic switching of electrode layers in the MTJ with the STO barrier layer. Conventional photolithography and ion milling were used to create a series of 4 μ m Hall bar tracks in the deposited films. Nanopillar devices, sized 250 nm × 250 nm, were successfully fabricated on these 4 μ m tracks by optimizing the FIB nanomachining technique. The fabricated MTJs demonstrated a high tunnel magnetoresistance (TMR) response, leading to the conclusion that the FIB nanomachining technique holds significant promise for the development of high-performance oxide-based spintronic devices. [ABSTRACT FROM AUTHOR]

Defects in the free layer are considered to be the main cause of the balloon effect, but there is little insight into the synthetic antiferromagnetic (SAF) layer. To address this shortcoming, in this work, an optimized SAF layer was introduced in the perpendicular magnetic tunneling junction (pMTJ) stack to eliminate the low-probability bifurcated-switching phenomenon. The results indicated that the Hf field in the film stack improved significantly from ~5700 Oe to ~7500 Oe. A magnetoresistive random access memory (MRAM) test chip was also fabricated with a 300 mm process, resulting in a significantly improved ballooning effect. The results also indicated that the switching voltage decreased by 18.6% and the writing energy decreased by 33.7%. In addition, the low-probability stray field along the x-axis was thought to be the main cause of the ballooning effect, and was experimentally optimized for the first time by enhancing the SAF layer. This work provides a new perspective on spin-flipping dynamics, facilitating a deeper comprehension of the internal mechanism and helping to secure improvements in MRAM performance. [ABSTRACT FROM AUTHOR]

Tunnel magnetoresistance (TMR) ratio is a key parameter characterizing the performance of a magnetic tunnel junction (MTJ), and a large TMR ratio is essential for the practical application of it. Generally, the traditional solutions to increasing the TMR ratio are to choose different material combinations as the ferromagnetic (FM) leads and nonmagnetic tunnel barrier. In this work, we study an architecture of MTJs of "FM/barrier/FM/barrier/FM" with double barriers, in contrast to the traditional single barrier structure "FM/barrier/FM." We first analytically show that double barrier MTJ will generally have much higher TMR ratio than the single barrier MTJ and then substantiate it with the well-known example of "Fe/MgO/Fe" MTJ. Based on density functional calculations combined with nonequilibrium Green's function technique for quantum transport study, in the single barrier "Fe/MgO/Fe" MTJ, the TMR ratio is obtained as 122%, while in the double barrier "Fe/MgO/Fe/MgO/Fe" MTJ, it is greatly increased to 802%, suggesting that double barrier design can greatly enhance the TMR and can be taken into consideration in the design of MTJs. [ABSTRACT FROM AUTHOR]

Ferromagnets with high spin polarization are known to be valuable for spintronics—a research field that exploits the spin degree of freedom in information technologies. Recently, antiferromagnets have emerged as promising alternative materials for spintronics due to their stability against magnetic perturbations, absence of stray fields, and ultrafast dynamics. For antiferromagnets, however, the concept of spin polarization and its relevance to the measured electrical response are elusive due to nominally zero net magnetization. Here, we define an effective momentum-dependent spin polarization and reveal an unexpected property of many noncollinear antiferromagnets to exhibit nearly 100% spin polarization in a broad area of the Fermi surface. This property leads to the emergence of an extraordinary tunneling magnetoresistance (ETMR) effect in antiferromagnetic tunnel junctions (AFMTJs). As a representative example, we predict that a noncollinear antiferromagnet Mn3GaN exhibits nearly 100% spin-polarized states that can efficiently tunnel through low-decay-rate evanescent states of perovskite oxide SrTiO3 resulting in ETMR as large as 104%. Our results uncover hidden functionality of material systems with noncollinear spin textures and open new perspectives for spintronics. In most collinear antiferromagnets, PT symmetry leads to a lack of spin-polarization. Here, Gurung et al show that a noncollinear antiferromagnets can exhibit an extremely high degree of spin polarization over a large area of its Fermi surface and propose using this feature for the development of antiferromagnetic magnetic tunnel junctions. [ABSTRACT FROM AUTHOR]

Magnetic memory based on spin‐orbit torque (SOT) is a promising candidate for the next‐generation storage devices. Materials that generate out‐of‐plane spin polarization (σz) are highly desired and actively pursued as the SOT generator, due to its ability to achieve field‐free SOT switching of perpendicular magnetization. However, integrating σz into perpendicular magnetic tunnel junction for efficient data writing is not realized. Here, utilizing σz from antiferromagnetic spin Hall effect in Mn2Au, σz‐enabled field‐free SOT switching of perpendicular magnetic tunnel junctions is realized demonstrating a magnetic memory with both writing and reading electrically. The tunnel magnetoresistance ratio achieves 66% with a critical current density of 5.6 × 106 A cm−2 at room temperature. Such field‐free fully SOT switching is further directly confirmed by domain imaging via magneto‐optical Kerr effect microscopy. In addition to enabling field‐free switching, σz is proposed to assist ultrafast and more efficient switching of perpendicular magnetization compared with conventional in‐planes ones, based on simulations. This research advances the application of out‐of‐plane SOTs and paves the way for high‐density, high‐speed, and low‐power magnetic memory. [ABSTRACT FROM AUTHOR]

A series of Pt/Co2FeSi/MgAl2O4/Pt thin films with Co2FeSi thicknesses ranging from 4.5 to 6 nm are constructed to evaluate the influence of applied voltage on magnetic coercivity. It is found that the change in coercivity is around 50.04% at an applied voltage of 16 V for a 5.5 nm thin film, but increases significantly to 72.24% for a 6 nm thin film. We show evolution of perpendicular magnetic anisotropy (PMA) properties of Co2FeSi amorphous thin films with varying thickness. The polarization of External Hall Effect (EHE) and Magneto-Optic Kerr Effect (MOKE) loops match well with magnetic hysteresis. The EHE coefficient Rs rises from 2.0 × 10–10 to 5.5 × 10–10 Ω cm/G with increase in thickness from 4 nm to 6.5 nm, respectively. The voltage controlled the magnetic properties of Co2FeSi thin films might be beneficial in the development of low-power magnetic tunnel junctions [MTJs]. [ABSTRACT FROM AUTHOR]

This article introduces an innovative non‐volatile associative memory (AM) that leverages spintronic synapses, employing magnetic tunnel junctions (MTJ) in conjunction with neurons constructed using carbon nanotube field‐effect transistors (CNTFETs). Our proposed design represents a significant advancement in area optimization and outperforms prior designs. We adopt MTJ‐based spintronic devices due to their remarkable attributes, including dependable reconfigurability and nonvolatility. Simultaneously, CNTFETs effectively address the longstanding limitations traditionally associated with MOSFETs. In this work, our proposed design undergoes rigorous simulations that account for process variations. The results demonstrate that our AM system closely approximates its ideal mathematical model, even with significant process variations. Furthermore, we investigate the impact of Tunnel Magnetoresistance (TMR) on the performance of our proposed AM system. Our investigations reveal that, even with a TMR as low as 100%, our design matches and often surpasses the performance of its counterparts operating with a TMR of 300%. This achievement holds profound significance from a fabrication standpoint, as fabricating MTJs with high TMR values can be intricate and costly. Overall, our novel AM system represents a significant breakthrough in emerging technologies, harnessing the unique strengths of spintronic synapses and advanced carbon nanotube transistors while robustly addressing challenges in performance and variability. [ABSTRACT FROM AUTHOR]

Magnetic skyrmions are particle-like topological protected spin structures that can be driven by electric current. We demonstrate a single skyrmion-based multilevel data storage device that could also work as the potential artificial synapse for neuromorphic computing. Four pinning sites are designed to situate the skyrmion in selective regions, whose resistances rise owing to the anisotropic magnetoresistance (AMR) induced by the skyrmion. Skyrmion's position could denote the data levels when the device works as a multilevel data storage device. Pinning sites' positions represent the synaptic weights when it functions as the artificial synapse. Multilevel data storage device's data level change or the synapse's potentiation and depression is realized by the electric current applied parallel to the track. Our work shows that the AMR could help to detect a single skyrmion without the magnetic tunnel junction. Moreover, the skyrmion manipulated by pinning provides an approach for precise control and helps realize skyrmion-based in-memory computing. [ABSTRACT FROM AUTHOR]

Field-free magnetization switching via the interplay of spin orbit torque (SOT), exchange bias field (H E X ), and voltage controlled magnetic anisotropy (VCMA) is crucial for the development of scalable, high speed, and energy-efficient spintronic memories. This has been experimentally demonstrated by the rapid evolution of the voltage gated-spin orbit torque-magnetic random access memory (VG-SOT-MRAM) cell, in which perpendicular spin current is fed along with the in-plane H E X and VCMA assistance for cell programming. Here, we have examined the writing properties of a three terminal voltage gated-spin orbit torque-perpendicularly magnetized magnetic tunnel junction (VG-SOT-pMTJ) device structure (IrMn/CoFeB/MgO/CoFeB) in-depth through simulation. We observed that SOT critical switching current (I _ S O T) decreases either by increasing the VCMA voltage or FL thickness. Even SOT field-like torque can accelerate the switching process and modulate the critical switching current. As the VCMA voltage rises, I _ S O T falls by nearly 60%. In our experimental setup, VCMA/SOT optimal pulse width and amplitude for better write delay are 1 ns and 0.3 V, respectively. Furthermore, the impacts of free layer thickness, pMTJ radius, H E X , and noise are analyzed. Finally, we demonstrate the dependency of material parameters on temperature and VCMA voltage. [ABSTRACT FROM AUTHOR]

We have developed and optimized two categories of spin-ransfer torque magnetic tunnel junctions (STT-MTJs) that exhibit a high tunnel magnetoresistance ratio, low critical current, high outputpower in the micro-watt range, and auto-oscillation behavior. These characteristics demonstrate the potential of STT-MTJs for low-power, high-speed, and reliable spintronic applications, including magnetic memory, logic, and signal processing. The only distinguishing factor between the two categories, denoted as A-MTJs and B-MTJs, is the composition of their free layers, two CoFeB/0.21 Ta/6 CoFeSiB for A-MTJs and two CoFeB/0.21 Ta/7 NiFe for B-MTJs. Our study reveals that B-MTJs exhibit lower critical currents for auto-oscillation than A-MTJs. We found that both stacks have comparable saturation magnetization and anisotropy field, suggesting that the difference in auto-oscillation behavior is due to the higher damping of A-MTJs compared to B-MTJs. To verify this hypothesis, we employed the all-optical time-resolved magneto-optical Kerr effect technique, which confirmed that STT-MTJs with lower damping exhibited auto-oscillation at lower critical current values. Additionally, our study aimed to optimize the STT-MTJ performance by investigating the impact of the capping layer on the device's response to electronic and optical stimuli. [ABSTRACT FROM AUTHOR]

The ubiquitous presence of electronic devices demands robust hardware security mechanisms to safeguard sensitive information from threats. This paper presents a physical unclonable function (PUF) circuit based on magnetoresistive random access memory (MRAM). The circuit utilizes inherent characteristics arising from fabrication variations, specifically magnetic tunnel junction (MTJ) cell resistance, to produce corresponding outputs for applied challenges. In contrast to Arbiter PUF, the proposed effectively satisfies the strict avalanche criterion (SAC). Additionally, the grid-like structure of the proposed circuit preserves its resistance against machine learning-based modeling attacks. Various machine learning (ML) attacks employing multilayer perceptron (MLP), linear regression (LR), and support vector machine (SVM) networks are simulated for two-array and four-array architectures. The MLP-attack prediction accuracy was 53.61% for a two-array circuit and 49.87% for a four-array circuit, showcasing robust performance even under the worst-case process variations. In addition, deep learning-based modeling attacks in considerable high dimensions utilizing multiple networks such as convolutional neural network (CNN), recurrent neural network (RNN), MLP, and Larq are used with the accuracy of 50.31%, 50.25%, 50.31%, and 50.31%, respectively. The efficiency of the proposed circuit at the layout level is also investigated for simplified two-array architecture. The simulation results indicate that the proposed circuit offers intra and inter-hamming distance (HD) with a mean of 0.98% and 49.96%, respectively, and a mean diffuseness of 49.09%. [ABSTRACT FROM AUTHOR]

The use of femtosecond laser pulses for ultrafast triggering of magnetization switching is of great interest in multilayer systems with great tunability. At present, the impact of interfacial mixing on magnetization switching has not been thoroughly investigated. In this paper, the impact of interfacial mixing on magnetization dynamics in multilayer systems is investigated by a combination of atomic spin dynamics and two-temperature models. Our results show that interfacial mixing in multilayer systems not only reduces the energy density required for magnetization switching but also expands the range of pulse durations that can trigger magnetization switching. In addition, we have investigated the dependence of the switching time on the interfacial mixing in multilayer systems. The results show that interfacial mixing can accelerate the process of magnetization dynamics, thus providing a theoretical basis for the design of faster speed optically controlled magnetic tunnel junctions. [ABSTRACT FROM AUTHOR]

With the advancement of technology nodes, the challenging space radiation environment poses a significant threat to memory reliability. Spin transfer torque magnetic random access memory (STT-MRAM) is a formidable candidate for non-volatile memory for space applications due to its advantages of non-volatility, durability, speed and compatibility with CMOS technology. Although the STT-MRAM memory unit magnetic tunnel junction (MTJ) is naturally immune to radiation effects, the single event upset (SEU) affects the peripheral circuitry. A radiation-hardened circuit is proposed, which theoretically does not have ‘0' upset nodes and automatically recovers from ‘1' upset. Moreover, the circuit's radiation-hardened performance was corroborated through hybrid simulation utilizing 40-nm technology. The findings of this investigation hold significance for the use of space radiation-hardened STT-MRAM. [ABSTRACT FROM AUTHOR]

Projective measurement of single-electron spins, or spin readout, is among the most fundamental technologies for spin-based quantum information processing. Implementing spin readout with both high-fidelity and scalability is indispensable for developing fault-tolerant quantum computers in large-scale spin-qubit arrays. To achieve high fidelity, a latching mechanism is useful. However, the fidelity can be decreased by spin relaxation and charge state leakage, and the scalability is currently challenging. Here, we propose and demonstrate a double-latching high-fidelity spin readout scheme, which suppresses errors via an additional latching process. We experimentally show that the double-latching mechanism provides significantly higher fidelity than the conventional latching mechanism and estimate a potential spin readout fidelity of 99.94% using highly spin-dependent tunnel rates. Due to isolation from error-inducing processes, the double-latching mechanism combined with scalable charge readout is expected to be useful for large-scale spin-qubit arrays while maintaining high fidelity. [ABSTRACT FROM AUTHOR]

We studied theoretically the tunneling of electrons in ZnO/ZnCdO semiconducting double-barrier heterostructure with the application of an external electric field. Induced Rasbha spin-orbit interaction (RSOI) caused the spin-separation in the considered heterostructure. The addition of the Dresselhaus spin-orbit interaction (DSOI) enhances the separation between the different spin orientations. Even without in-built Rasbha spin-orbit interaction, one can obtain 100% spin-polarization efficiency in this heterostructure. The DSOI enhances the separation between spin-up and spin-down electrons on the energy scale. The increasing electric field reduces the energy of resonance spin-polarization and it reduces the spin-separation. The results might be helpful for the fabrication of ZnO-based spintronic devices. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junctions are nanoscale devices that have recently attracted interest in the context of frequency multiplexed spintronic neural networks, due to their interesting dynamical properties, which are defined during the fabrication process, and depend on the material parameters and geometry. This work proposes an approach to extending the functionality of a standard magnetic tunnel junction (MTJ) by introducing an additional ferromagnet/antiferromagnet (FM/AFM) storage layer (SL) vertically integrated with the standard vortex MTJ stack into the nanopillar. The magnetostatic field created by this storage layer acts on the free layer and can be used to change its static and dynamic properties. To tune the magnitude and direction of this magnetostatic field, magnetic reconfiguration is carried out through a thermally assisted switching mechanism using a voltage pulse that heats the AFM layer in the SL above the Néel temperature in the presence of an external field. It is experimentally shown that using an MTJ based on a 600 nm diameter nanopillar with a vortex in the free layer, reconfiguration of the SL allows to continuously change the core precession frequency in the 15 MHz range, or ≈10% of the device frequency. [ABSTRACT FROM AUTHOR]

We report the structural feature of sputter-deposited epitaxial [Co (0.2 nm)/Pt (0.2–1.0 nm)] multilayered films prepared with various periodic structural designs consisting of non-integer numbers of Co and Pt monoatomic layers on an atomically flat Ru(0001). Sharp superlattice modulation peaks and their systematic changes with the Pt thicknesses were observed in the x-ray diffraction (XRD) spectrum. The formation of periodic structures shows that layer-by-layer like growth occurs and the resulting incommensurate superlattice modulation survives down to an atomic scale even in the sputter-deposited Co/Pt multilayers. Magnetic properties were also investigated for the Co/Pt multilayers. Interestingly, the maximum perpendicular magnetic anisotropy Ku of 3 × 106 erg/cm3 was obtained for the [Co (0.2 nm)/Pt (0.3 nm)] multilayer exhibiting incommensurate superlattice modulation peaks, while the [Co (0.2 nm)/Pt (0.2 nm)] multilayer with a L11-like XRD peak showed a smaller Ku. A cross-sectional high-angle annular dark-field scanning transmission electron microscopy analysis revealed that a partially L11-ordered CoPt structure is formed in the [Co 0.2 nm/Pt 0.2 nm] multilayer, interpreting the observed Ku. This study gives a new insight into the structural feature of sputter-deposited Co/Pt multilayers useful for a wide range of spintronic devices, such as magnetic tunnel junctions. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junction (MTJ)-based true random number generators (TRNG), which are promisingly utilized as hardware accelerators for probabilistic computing, may suffer intrinsic performance drifting and fluctuation in the probability space and performance variations in device arrays. In order to preventively avoid these concerns, it is necessary to develop strategies that can help MTJ-based TRNG to be self-stabilized and calibration-free. Here, we derived a simple and easily handleable strategy that only depends on the current sampled state of an MTJ device without any historical or statistic information or a pre-calibrated probabilistic switching property to dynamically tune its sampling probability for the next sampling operation. In this way, the long-term sampling probability of the MTJ can be proved to automatically converge into a desired probability with little fluctuation and drifting. We further experimentally demonstrate such a self-stabilized MTJ-based TRNG. Our results show that the TRNG can generate binary random numbers with any destined probability regardless of its initial state. Furthermore, the TRNG also displays the desired capability of excellently hedging against performance drifting and fluctuations. All these combined allow the self-stabilized TRNG without calibration to be more viable for high-quality entropy source applications. [ABSTRACT FROM AUTHOR]

Memristors have emerged as promising devices for enabling efficient multiply-accumulate (MAC) operations in crossbar arrays, crucial for analog in-memory computing (AiMC). However, variations in memristors and associated circuits can affect the accuracy of analog computing. Typically, this is mitigated by on-chip training, which is challenging for memristors with limited endurance. We present a hardware-software codesign using magnetic tunnel junction (MTJ)-based AiMC off-chip calibration that achieves software accuracy without costly on-chip training. Hardware-wise, MTJ devices exhibit ultralow cycle-to-cycle variations, as experimentally evaluated over 1 million mass-produced devices. Software-wise, leveraging this, we propose an off-chip training method to adjust deep neural network parameters, achieving accurate AiMC inference. We validate this approach with MAC operations, showing improved transfer curve linearity and reduced errors. By emulating large-scale neural network models, our codesigned MTJ-based AiMC closely matches software baseline accuracy and outperforms existing off-chip training methods, highlighting MTJ's potential in AI tasks. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junctions (MTJs) are widely applied in spintronic devices for efficient spin detection through the imbalance of spin polarization at the Fermi level. The van der Waals (vdW) property of 2D magnets with atomically flat surfaces and negligible surface roughness greatly facilitates the development of MTJs, primarily in ferromagnets. Here, A‐type antiferromagnetism in 2D vdW single‐crystal (Fe0.8Co0.2)3GaTe2 is reported with TN ≈ 203 K in bulk and ≈ 185 K in 9‐nm nanosheets. The metallic nature and out‐of‐plane magnetic anisotropy make it a suitable candidate for MTJ electrodes. By constructing heterostructures based on (Fe0.8Co0.2)3GaTe2/WSe2/Fe3GaTe2, a large tunneling magnetoresistance (TMR) ratio of 180% at low temperature is obtained, with the TMR signal persisting at near‐room temperature 280 K. Furthermore, the TMR is tunable by the electric field, and the MTJ device operates stably with a low applied bias down to 1 mV (≈0.6 nA), highlighting its potential for energy‐efficient spintronic devices. This work opens up new opportunities for 2D antiferromagnetic spintronics and quantum devices. [ABSTRACT FROM AUTHOR]

Herein, analytical modeling of Fe3O4/x(≈1.1 nm)/Co (x = rubrene, C60, and bathocuproine (BCP)) magnetic tunnel junctions (MTJs) has been performed using rubrene, C60, and BCP as organic spacer layers. The simulation is considered as nonequilibrium Green's function assuming spin precession at ferromagnet/organic semiconductor (FM/OSC) interface defect states. The voltage‐dependent resistances for both parallel (RP) and antiparallel (RAP) orientations have been observed to be dependent on spin injection from FM/OSC defect states. Pinning well‐dependent defect state depths have been associated with band misalignment‐induced lattice distortion at FM/OSC interface of the devices. The large tunnel magnetoresistance (TMR) response for rubrene‐based MTJ device has been attributed to a higher change of FM/OSC defect state depths with voltage. High TMR may have reduced spin torque‐dependent spin precession, leading to lower spin transfer torque for the rubrene device. Hence, engineering of defect states at the FM/OSC interface may lead to the successful realization of enhanced TMR in organic spacer MTJs for high‐performance spintronic memory applications. [ABSTRACT FROM AUTHOR]

Magnetic van der Waals (vdW) materials have attracted massive attention because of their academic interest and application potential for the past few years. Its main advantage is the intrinsic two‐dimensionality, enabling much smaller devices of novel concepts. One particular exciting direction lies in the current‐driven spin‐orbit torque (SOT). Here, for the first time, all vdW three‐terminal SOT memory is realized, employing the unique physics principle of gigantic intrinsic SOT of Fe3GeTe2 (FGT) and the well‐known industry‐adopted tunneling magnetoresistance (TMR) effect. The device operation procedure is designed and the FGT/h‐BN/FGT vdW heterostructure is fabricated as a proof of concept. This device exhibits a classical TMR effect and unambiguously demonstrates the conception by precise performance as expected: the magnetic information of the top‐FGT is written by current‐driven SOT and read out by TMR separately. The writing and reading current paths are physically decoupled, enhancing the design and optimization flexibility substantially and further strengthening the device's endurance naturally. The work will prompt more expansive use of vdW magnets for spintronic applications. [ABSTRACT FROM AUTHOR]

This paper theoretically examines the impact of integrating 2D transition metal dichalcogenide (TMDCs) materials—MoS2, MoSe2, MoTe2, WS2, and WSe2—with a conventional MgO dielectric to fabricate double-barrier penta-layer (DBPL) magnetic tunnel junction (MTJ) structures. The MTJ device proposed herein is distinguished by a DBPL configuration which incorporates the composite tunnel barrier (CTB) of MgO-MX2-MgO sandwiched between the Fe ferromagnetic electrodes. Using density functional theory (DFT), we conducted a crystallographic analysis on all constituent materials to predict the properties necessary for device operation. Subsequent simulations leveraged an advanced nonequilibrium Green's function-based (NEGF) quantum transport simulator to quantify critical transport phenomena. Notable metrics such as tunneling magnetoresistance (TMR), differential TMR, and spin-transfer torque (STT), both in-plane and out-of-plane, were determined. Additionally, resistance and differential resistance profiles for parallel and antiparallel alignment states were thoroughly evaluated. Our findings elucidate the essential role of CTB composition in determining MTJ performance attributes, with particular dielectric pairings showing a significant enhancement in TMR ratios and an improved resistance differential without compromising the efficiency of STT. Interestingly, our proposed MTJ device shows a substantial increase in TMR values, ranging from 900% to 4300%, with very high sensitivity ranging from 7.33 × 106 T−1 to 3.36 × 107 T−1. [ABSTRACT FROM AUTHOR]

This paper presents the results of studies of the effects of magnetoresistance and magnetocapacitance in magnetic tunnel junctions Tb 2 2 − δ Co5 Fe 7 3 /Pr6 O 1 1 / Tb 1 9 − δ Co5 Fe 7 6 with perpendicular anisotropy of magnetic electrodes and a paramagnetic barrier layer. Experimentally measured values of tunnel magnetic resistance and tunnel magnetic capacitance in such contacts exceed 100% at room temperature. The paper analyzes the effect of magnetization reversal of one of the electrodes on the conductivity of magnetic tunnel junctions with electrodes that have perpendicular anisotropy. It is shown that significant changes in tunnel magnetic resistance and tunnel magnetic capacity in such contacts can be explained by the separation of electrons with major and minor spin polarization in the inverse nanolayer in the interface region. The separation of polarized electrons is caused by the magnetomotive force acting on the electron spin in a strongly gradient magnetic field. Such a magnetomotive force occurs with antiparallel magnetization of the magnetic electrodes and it has opposite directions for major and minor polarized electrons. As a result of the spatial separation of polarized electrons in the inversion layer, an inhomogeneous distribution of the electron density along the direction of magnetization of the magnetic contacts occurs. As a result, an additional Coulomb barrier between the magnetic electrodes and the dielectric nanolayer appears in the tunnel contacts and an additional spin capacitance appears. [ABSTRACT FROM AUTHOR]

The growing utilization of neural networks has led to a heightened focus on the hardware implementation of such networks. Security concerns associated with these implementations pose a significant challenge in this regard. Among these problems, the vulnerability of these networks against side-channel attacks such as power attacks can be mentioned. This paper presents a technique to enhance the resilience of hardware implementations of neural networks, particularly Hopfield neural networks, to mitigate the risks posed by power attacks. In addition to the fact that the proposed method makes it impossible to attack the network, it also reduces the power consumption of the entire circuit by reducing the leakage currents. The simulation results demonstrate that the proposed approach also achieves about a 10% reduction in energy consumption while concurrently improving the accuracy of the implemented associative memory by 1.1%. [ABSTRACT FROM AUTHOR]

With the outstanding growth of Internet of Things (IoT) devices, security and power efficiency of integrated circuits can no longer be overlooked. Current approved standards for cryptographic algorithms are not suitable for constrained environments. In this context, the National Institute of Standards and Technology (NIST) started a lightweight cryptography (LWC) competition to develop new algorithm standards that can be fit into small devices. In 2023, NIST has decided to standardize the Ascon family for LWC. This algorithm has been designed to be more resilient to side-channel and fault-based analysis. Nonetheless, hardware implementations of Ascon have been broken by multiple statistical fault analysis and power analysis. These attacks have underlined the necessity to develop adapted countermeasures to side-channel and perturbation-based attacks. However, existing countermeasures are power and area consuming. In this article, we propose a new countermeasure for the Ascon cipher that does not significantly increase the area and power consumption. Our architecture relies on the nonvolatile feature of the Magnetic Tunnel Junction (MTJ) that is the single element of the emerging Magnetic Random Access Memories (MRAM). The proposed circuit removes the bias exploited by statistical attacks. In addition, we have duplicated and complemented the permutation of Ascon to enhance the power analysis robustness of the circuit. Besides the security aspect, our circuit can save current manipulated data, ensuring energy saving from 11% to 32.5% in case of power failure. The area overhead, compared to an unprotected circuit, is × 2.43 . [ABSTRACT FROM AUTHOR]

We report systematic investigations of the effect of ultrathin capping layer insertion on the magnetic, magnetotransport, and voltage-controlled magnetic anisotropy (VCMA) properties in magnetic tunnel junctions (MTJs) with top free layer structure. Various kinds of ultrathin capping materials (Ir, Mo, TaB, Mg, Cr, Ti, and Ta) were introduced into the top free layer structure, which is comprised of MgO/CoFeB/X/MgO, where X is the inserted capping material. On insertion of an ultrathin Ir capping layer thinner than 0.3 nm, both the perpendicular magnetic anisotropy and the VCMA efficiency were improved by approximately a factor of two compared to the case without inserting an ultrathin metal capping layer. Mo insertion was also seen to be effective in improving the annealing tolerance. The developed structure can provide a novel approach for the development of high-performance voltage-driven MTJs, which can be applied, for example, for voltage-controlled magnetoresistive random access memory. [ABSTRACT FROM AUTHOR]

The discovery of van der Waals intrinsic magnets has expanded the possibilities of realizing spintronics devices. We investigate the transmission, tunneling magnetoresistance ratio, and spin injection efficiency of bilayer LaI2 using a combination of first-principles calculations and the non-equilibrium Green's function method. Multilayer graphene electrodes are employed to build a magnetic tunnel junction with bilayer LaI2 as ferromagnetic barrier. The magnetic tunnel junction turns out to be a perfect spin filter device with an outstanding tunneling magnetoresistance ratio of 653% under a bias of 0.1 V and a still excellent performance in a wide bias range. In combination with the obtained high spin injection efficiency this opens up great potential from the application point of view. [ABSTRACT FROM AUTHOR]

We present a spintronic device based hardware implementation of UNet for segmentation tasks. Our approach involves designing hardware for convolution, deconvolution, rectified activation function (ReLU), and max pooling layers of the UNet architecture. We designed the convolution and deconvolution layers of the network using the synaptic behavior of the domain wall MTJ. We also construct the ReLU and max pooling functions of the network utilizing the spin hall driven orthogonal current injected MTJ. To incorporate the diverse physics of spin-transport, magnetization dynamics, and CMOS elements in our UNet design, we employ a hybrid simulation setup that couples micromagnetic simulation, non-equilibrium Green's function, and SPICE simulation along with network implementation. We evaluate our UNet design on the CamVid dataset and achieve segmentation accuracies of 83.71% on test data, on par with the software implementation with 821 mJ of energy consumption for on-chip training over 150 epochs. We further demonstrate nearly one order of magnitude (10×) improvement in the energy requirement of the network using unstable ferromagnet (Δ = 4.58) over the stable ferromagnet (Δ = 45) based ReLU and max pooling functions while maintaining similar accuracy. The hybrid architecture comprising domain wall MTJ and unstable FM-based MTJ leads to an on-chip energy consumption of 85.79 mJ during training, with a testing energy cost of 1.55 µJ. [ABSTRACT FROM AUTHOR]

This work investigates the interplay between interfacial spin–orbit coupling (SOC) and magnon excitation-induced spin memory loss in epitaxial L10-FePt/MgO/L10-FePt magnetic tunnel junctions, which is crucial for advancing spintronic technologies. By employing systematic temperature-dependent transport measurements and inelastic electron tunneling spectroscopy, our study reveals that interfacial SOC at the Pt-terminated FePt/MgO interface significantly enhances magnon excitation during electron tunneling. This process results in a pronounced loss of spin memory in the spin-polarized current, diminishing the tunnel magnetoresistance ratio. Our findings provide critical insights into the mechanisms of spin memory loss, offering directions for optimizing spintronic device performance in the context of pronounced SOC environments. [ABSTRACT FROM AUTHOR]

Hardware-based acceleration approaches for Machine Learning (ML) workloads have been embracing the significant potential of post-CMOS switching devices to attain reduced footprint and/or energy-efficient execution relative to transistor-based GPU and/or TPU-based accelerator architectures. Meanwhile, the promulgation of fabless IC chip manufacturing paradigms has heightened the hardware security concerns inherent in such approaches. Namely, unauthorized access to various supply chain stages may expose significant vulnerabilities resulting in malfunctions including subtle adversarial outcomes via the malicious generation of differentially-corrupted outputs. Whereas the Spin-Orbit Torque Magnetic Tunnel Junction (SOT-MTJ) is a leading spintronic device for use in ML accelerators, as well as holding security tokens, their manufacturing-only security exposures are identified and evaluated herein. Results indicate a novel vulnerability profile whereby an adversary without access to the circuit netlist could differentially-influence the machine learning application's behavior. Specifically, ML recognition outputs can be significantly swayed via a global modification of oxide thickness (Tox) resulting in bit-flips of the weights in the crossbar array, thus corrupting the recognition of selected digits in MNISTdataset differentially creating an opportunity for an adversary. With just 0.05% of bits in crossbar having a flipped resistance state, digits "4" and "5" show the highest overall error rates, and digit "9" exhibit the lowest impact, with recognition accuracy of digits "2," "3," and "8" unaffected by changing the oxide thickness of SOT-MTJs uniformly from 0.75 nm to 1.2 nm without modifying the netlist nor even having access to the circuit design itself. Exposures and mitigation approaches to such novel and potentially damaging manufacturing-side intrusions are identified, postulated, and quantitatively assessed. [ABSTRACT FROM AUTHOR]

An alternative way of skyrmion quasi-particle detection is simulated at low voltage bias. The point contact (PC), attached to the strip with a Néel-type skyrmion, can detect it with a higher efficiency than a magnetic tunnel junction. The method is based on detecting the skyrmion via the ballistic magnetoresistance ratio (BRR). PC's resistance with skyrmion significantly differs from the one without it. BRR is estimated in the framework of the point contact model for two directions of spin-polarized current: perpendicular to the transport direction (case 1) and along one (case 2). Skyrmion's size is assumed to be around 3.6 nm in diameter—smaller, or comparable, to the mean free path of electrons, allowing it to utilize the ballistic transport approach. As a result, resistance values for the considered Néel type skyrmion within the related size are estimated as 157 Ω for case 1 and 452.2 Ω for case 2 with optimistic BRR 101.3% and 291.7%, respectively. BRR for case 2 is higher due to the spin-filtering effect. The method also has the potential to detect the skyrmion type, or other magnetic nano structures such as bimeron, domain wall (DW), etc. [ABSTRACT FROM AUTHOR]

This work shows how the tunnel-effect based magnetoresistance (TMR) technology can be used as a competitive sensing method in electrical current and power processors. The sensor is arranged in a Wheatstone bridge topology, and each magnetoresistance was composed of a series connection of 360 magnetic tunnel junction elements with the following structure (thickness in nm): 100 SiO2/5 Ta/15 Ru/5 Ta/15 Ru/5 Ta/5 Ru/20 IrMn/2 CoFe30/0.85 Ru/2.6 CoFe40B20/1.2 MgO/2 CoFe40B20/0.21 Ta/4 NiFe/0.20 Ru/6 IrMn/2 Ru/5 Ta/10 Ru. First, the electrical and thermal characteristics of the sensor were evaluated by analyzing its response to DC current sweeps at various temperatures, controlled using a climatic chamber. Nominal values of current sensitivity S (0.324 mV/A), bridge output offset voltage Vo,s,o (−37.1 mV), bridge input resistance Rinp,bridge (0.958 kΩ), and their thermal behavior were obtained (0.0036 mV/A°C, 0.079 mV/°C, and −0.31 Ω/°C). Second, an instrumentation system is introduced to characterize the sensor, measuring its sensitivity to AC line currents from the mains up to 10 Arms. Finally, an electronic wattmeter was developed showing the relevant quantities of its design. The circuit is able to interface a TMR Wheatstone bridge to an analog processor. Power and current measurements were obtained from a 150 Vrms AC mains 1.5 kW load with resistive and capacitive components, achieving less than 1% deviation over the expected values. The circuit shown can be used to interface these signals to more complex smart digital engines with active or reactive energy processing capabilities, while providing inherent high voltage isolation, thanks to its TMR measurement technology. [ABSTRACT FROM AUTHOR]

Magnetic Josephson junctions (MJJs) are a special class of hybrid systems where antagonistic correlations coexist, thus providing a key for advances in weak superconductivity, superconducting spintronics, and quantum computation. So far, the memory properties of MJJs have been mostly investigated in view of digital electronics and for spintronic devices at liquid-helium temperature. At the operating temperature of quantum circuits, a magnetic order can rise in a superconductor (S) at the S/ferromagnet (F) interface, i.e., the inverse proximity effect (IPE), thus leading to a significant modification of the magnetic field patterns in MJJs. In this work, we have carried out a comparative investigation of the magnetic behavior of tunnel MJJs with a strong ferromagnetic layer inserted in the layout of both Nb and Al JJs, respectively. The comparative analysis validates the crucial role of the temperature, the fundamental scaling energies of S/F coupling systems, and the transparency of the S/F interface. This investigation points out that the IPE is a key aspect to consider when designing tunnel MJJs operating well below 4 K and thus in the perspective of hybrid superconducting quantum architectures. [ABSTRACT FROM AUTHOR]