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Abstract Extending Moore’s law by augmenting complementary-metal-oxide semiconductor (CMOS) transistors with emerging nanotechnologies (X) has become increasingly important. One important class of problems involve sampling-based Monte Carlo algorithms used in probabilistic machine learning, optimization, and quantum simulation. Here, we combine stochastic magnetic tunnel junction (sMTJ)-based probabilistic bits (p-bits) with Field Programmable Gate Arrays (FPGA) to create an energy-efficient CMOS + X (X = sMTJ) prototype. This setup shows how asynchronously driven CMOS circuits controlled by sMTJs can perform probabilistic inference and learning by leveraging the algorithmic update-order-invariance of Gibbs sampling. We show how the stochasticity of sMTJs can augment low-quality random number generators (RNG). Detailed transistor-level comparisons reveal that sMTJ-based p-bits can replace up to 10,000 CMOS transistors while dissipating two orders of magnitude less energy. Integrated versions of our approach can advance probabilistic computing involving deep Boltzmann machines and other energy-based learning algorithms with extremely high throughput and energy efficiency.

The transistor celebrated its 75th birthday in 2022. The continued scaling of the transistor defined by Moore’s law continues, albeit at a slower pace. Meanwhile, computing demands and energy consumption required by modern artificial intelligence (AI) algorithms have skyrocketed. As an alternative to scaling transistors for general-purpose computing, the integration of transistors with unconventional technologies has emerged as a promising path for domain-specific computing. In this article, we provide a full-stack review of probabilistic computing with p-bits as a representative example of the energy-efficient and domain-specific computing movement. We argue that p-bits could be used to build energy-efficient probabilistic systems, tailored for probabilistic algorithms and applications. From hardware, architecture, and algorithmic perspectives, we outline the main applications of probabilistic computers ranging from probabilistic machine learning (ML) and AI to combinatorial optimization and quantum simulation. Combining emerging nanodevices with the existing CMOS ecosystem will lead to probabilistic computers with orders of magnitude improvements in energy efficiency and probabilistic sampling, potentially unlocking previously unexplored regimes for powerful probabilistic algorithms.

Since the qubit’s performance of solid-state spin centers depends highly on the host material, spin centers using new host materials may offer new qubit applications. We investigate the optical properties of Ce-implanted MgO and MgAl _2 O _4 as potential materials holding the optically accessible qubit. We find that the photoluminescence of Ce-implanted MgAl _2 O _4 is more than 10 times brighter than that of Ce-implanted MgO and observe polarization-dependent emission of Ce center in MgAl _2 O _4 with 2% at 4 K under 500 mT, suggesting that the properties required for initializing and reading the state of the spin qubit have been achieved.

Stochastic magnetic tunnel junctions (s-MTJs) are attracting attention as key elements for spintronics-based probabilistic (p-) computers. The performance of p-computers is governed by the time-domain and the time-averaged response of single s-MTJs varying with temperature. Here we present results of the time-domain (rf) voltage and time-averaged (dc) resistance $\left\langle R\right\rangle $ of s-MTJs with perpendicular magnetization as functions of perpendicular magnetic fields H _z and temperatures T = 20 °C–130 °C. We observe that both relaxation time (time-domain response) and the slope of the $\left\langle R\right\rangle $ – ${H}_{z}$ curve (time-averaged response) decrease with increasing temperature. We discuss the physics underlying these results including the thermally induced spatially non-uniform collective spin dynamics.

There has been much interest in using the probabilistic switching of magnetic tunnel junctions in unconventional computing, but to do so requires a detailed understanding of this switching. Here, Funatsu et al rigorously determine the switching exponents in superparamagnetic tunnel junctions.

Abstract Two-dimensional (2D) van der Waals (vdW) magnetic materials have attracted a lot of attention owing to the stabilization of long range magnetic order down to atomic dimensions, and the prospect of novel spintronic devices with unique functionalities. The clarification of the magnetoresistive properties and its correlation to the underlying magnetic configurations is essential for 2D vdW-based spintronic devices. Here, the effect of Co-doping on the magnetic and magnetotransport properties of Fe3GeTe2 have been investigated. Magnetotransport measurements reveal an unusual Hall effect behavior whose strength was considerably modified by Co-doping and attributed to arise from the underlying complicated spin textures. The present results provide a clue to tailoring of the underlying interactions necessary for the realization of a variety of unconventional spin textures for 2D vdW FM-based spintronics.

Spin torque oscillators (STOs) are attractive potential alternative for many high frequency applications, due to their small area and CMOS compatibility. Here, Sharma et al succeed in the electrical synchronization of four STOs, and use their setup to demonstrate wireless and battery-free energy harvesting using eight STOs.

Spin Hall nano-oscillators can be tuned via magnetic fields and the drive current, but individual oscillator control in large arrays remains a challenge. Here, the authors provide individual control of the threshold current and the auto-oscillation frequency by voltage-controlled magnetic anisotropy.

Realizing stable, room-temperature magnetic skyrmions that can be moved along current is challenging. Here, the authors observe skyrmion bubbles in a synthetic antiferromagnetic coupled multilayer at room temperature and demonstrate its current-induced motion free from the skyrmion Hall effect.

We investigate the relationship between structural parameters, magnetic ordering, and the anomalous Hall effect (AHE) of Mn3+xSn1−x (−0.42 ≤ x ≤ +0.23) thin films annealed at various temperatures Ta. The crystal structure changes with x and Ta, and at Ta ≥ 500 °C near the stoichiometric composition (−0.08 ≤ x ≤ +0.04), epitaxial single-phase D019-Mn3+xSn1−x(101̄0) is obtained. At room temperature, a larger AHE is obtained when the single-phase epitaxial Mn3Sn with the lattice constant closer to that of bulk is formed. The temperature dependence of the AHE shows different behaviors depending on Ta and can be explained by considering the variation of magnetic ordering. A close inspection into the temperature and composition dependence suggests a variation of magnetic phase transition temperature with composition and/or a possible correlation between the AHE and Fermi level position with respect to the Weyl points. Our comprehensive study on (101̄0)-oriented epitaxial Mn3Sn thin films would provide the basis for utilizing the unique functionalities of non-collinear antiferromagnetic materials.

Spin defect centers with long quantum coherence times (T2) are key solid-state platforms for a variety of quantum applications. Cluster correlation expansion (CCE) techniques have emerged as a powerful tool to simulate the T2 of defect electron spins in these solid-state systems with good accuracy. Here, based on CCE, we uncover an algebraic expression for T2 generalized for host compounds with dilute nuclear spin baths under a magnetic field that enables a quantitative and comprehensive materials exploration with a near instantaneous estimate of the coherence time. We investigated more than 12,000 host compounds at natural isotopic abundance and found that silicon carbide (SiC), a prominent widegap semiconductor for quantum applications, possesses the longest coherence times among widegap nonchalcogenides. In addition, more than 700 chalcogenides are shown to possess a longer T2 than SiC. We suggest potential host compounds with promisingly long T2 up to 47 ms and pave the way to explore unprecedented functional materials for quantum applications. [ABSTRACT FROM AUTHOR]

INTRODUCTION: Incorporation of a plant-based diet was effective in both induction and short-term relapse prevention in Crohn's disease. Ten-year long-term relapse-free rates in Crohn's disease are around 10% to 23%. OBJECTIVE: We investigated whether infliximab and plant-based diet as first-line therapy enhance the long-term relapse-free rate in patients with Crohn's disease. METHODS: This single-group, prospective study was performed in tertiary hospitals in Japan. Remission was induced in 24 consecutive newly diagnosed adult patients with Crohn's disease during hospitalization via 3 standard infliximab infusions together with a plant-based diet. Patients were instructed to continue the diet after discharge. Scheduled maintenance infliximab infusion was not used. The primary endpoint was relapse, which was defined as the appearance of symptoms resulting in the alteration of therapeutic modality. The secondary endpoints were C-reactive protein level, plant-based diet score, and surgery. RESULTS: The median follow-up period was 8.6 years. Thirteen cases were relapse-free. The relapse-free rate evaluated by Kaplan-Meier survival analysis at 1, 2, 3, and 4 years was 79%, 66%, 57%, and 52%, respectively. There was no further reduction afterward up to 10 years. The relapse-free rate with normal C-reactive protein levels at 1 to 2 and 3 to 10 years was 57% and 52%, respectively. The plant-based diet score at 20 months and 5 years was significantly higher relative to baseline (p < 0.0001). Surgical rates at 5 and 10 years were 12% and 19%, respectively. CONCLUSIONS: Infliximab and plant-based diet as first-line therapy created an unprecedented relapse-free course in nearly half of patients with Crohn's disease. [ABSTRACT FROM AUTHOR]

Introduction: We regard inflammatory bowel disease as a lifestyle disease mainly mediated by a westernized diet. We developed a plant-based diet (PBD) to counter the westernized diet. PBD can induce remission without medication in a subset of mild cases of ulcerative colitis. Medication is provided when induction of remission is not achieved solely with PBD. We describe such a case in this report. Case Presentation: A 34-year-old woman visited us in October 2016 with a complaint of loose stool for nearly 5 years. Laboratory examination revealed mild abnormalities including elevation of C-reactive protein (CRP). Ulcerative colitis was diagnosed due to diffuse colonic inflammation and pathological findings consistent with ulcerative colitis. She was admitted for educational hospitalization for 19 days in the middle of November, during which PBD was provided. A few days after admission, her stool became normal. CRP concentration decreased to within the normal range. However, colonoscopy on discharge showed minimum improvement. Thereafter, CRP was abnormal on three successive occasions, and her stool alternated between normal and loose. Sulfasalazine was initiated at the end of March 2017. Thereafter, her stool was normally formed, and CRP decreased to normal. Endoscopic remission was confirmed in August. Her PBD score, which evaluates adherence to PBD, was 8 before admission, and 37 and 16 at 7 and 21 months after discharge, respectively. Conclusion: Medication was administered when restoration of a healthy dietary lifestyle was insufficient to induce remission. Our stepwise treatment makes the shift from one-size-fits-all medication toward medication to the right patient. [ABSTRACT FROM AUTHOR]

Introduction: About one-third of patients with severe ulcerative colitis (UC) do not respond to corticosteroid therapy and receive rescue therapy with infliximab or cyclosporine. Up to 20% of such patients fail to respond to rescue therapy and undergo colectomy. Objective: We investigated the outcomes of infliximab and a plant-based diet (PBD) as first-line therapy for severe UC. Methods: Patients with severe UC defined by the Truelove and Witts criteria were admitted and given standard induction therapy with infliximab (5.0 mg/kg-7.5 mg/kg) at 0, 2, and 6 weeks. Additionally, they received a PBD. The primary endpoint was remission or colectomy in the induction phase and 1 year after discharge. Secondary endpoints were changes in inflammatory markers in the induction phase and the PBD score at baseline and follow-up. A higher PBD score indicates greater adherence to a PBD. Results: Infliximab and PBD as first-line therapy was administered in 17 cases. The remission rate was 76% (13/17), and the colectomy rate was 6% (1/17) in the induction phase. C-reactive protein values and the erythrocyte sedimentation rate significantly decreased at week 6 from 9.42 mg/dL to 0.33 mg/dL and from 59 to 17 mm/h, respectively (p < 0.0001). At 1-year follow-up, the cumulative relapse rate was 25%, and there were no additional colectomy cases. Mean PBD scores of 27.7 at 1 year and 23.8 at 4 years were significantly higher than baseline scores of 8.3 and 9.9, respectively (p < 0.0001 and p = 0.0391). Conclusion: This new first-line therapy for severe UC demonstrated a higher remission rate and lower colectomy rate than with the current modality. [ABSTRACT FROM AUTHOR]

The magnetization of an array of 16 elongated iron nanoparticles are measured by a submicron semiconductor Hall magnetometer and the details of hysterisis curves and the angular dependence of magnetization switching fields are discussed. The results suggest that the magnetization reversal in these nanoparticles cannot be explained with a single coherent rotation mode, especially at low angles.

Context: No known previous study has focused on plant-based diet (PBD) to prevent relapse of ulcerative colitis (UC) except our previous educational hospitalization study. Objective: To describe the relapse rate in a large case series of UC after incorporation of PBD into induction therapy. Design: All patients with UC between 2003 and 2017 were admitted for induction therapy. Patients receiving educational hospitalization or treated with infliximab were excluded. A lacto-ovo-semivegetarian diet (PBD) together with medication prescribed according to UC guidelines was provided during hospitalization. Main Outcome Measures: The primary endpoint was relapse during follow-up. The secondary endpoint was change over time in the plant-based diet score (PBDS), which evaluated adherence to the PBD. Results: Ninety-two cases were studied, of which 51 were initial episodes and 41 were relapses. Cases varied in severity (31 mild, 48 moderate, 13 severe) and extent (15 proctitis, 22 left-sided colitis, 55 extensive colitis). More severe cases existed among the relapse cases than among the initial episode cases. Cumulative relapse rates at 1- and 5-year follow-up (Kaplan-Meier analysis) were 14% and 27%, respectively, for the initial episode cases, and 36% and 53%, respectively, for relapse cases. At long-term follow-up (6 years 4 months), PBDS was significantly higher than baseline PBDS (p < 0.0001). Conclusion: Relapse rates in UC after induction therapy with PBD were far lower than those previously reported with conventional therapy. Adherence to PBD was significantly higher than baseline even at 6-year follow-up. We conclude PBD is effective for preventing UC relapse. [ABSTRACT FROM AUTHOR]

Context: No known published study has focused on a plantbased diet (PBD) in the treatment of ulcerative colitis (UC). Objective: To investigate relapse prevention in UC after consumption of a PBD during educational hospitalization in Japan. Design: Prospective study of patients with mild UC or UC in remission who did not need immediate treatment. A PBD and dietary guidance were provided during a two-week hospitalization. Main Outcome Measures: The primary end point was relapse (a flare-up that required more aggressive treatment) during the follow-up period. Kaplan-Meier analysis was used to calculate the cumulative relapse rate. Secondary end points were immediate improvement in symptoms or laboratory data during hospitalization and a chronologic change in the PBD score, which evaluated adherence to the PBD. Results: Sixty cases were studied: 29 initial episode cases and 31 relapse cases. Of these, 31 involved proctitis; 7, left-sided colitis; and 22, extensive colitis. Thirty-seven patients were receiving medication; 23 were not. The median age was 34 years; median follow-up was 3 years 6 months. Eight cases relapsed during followup. The cumulative relapse rates at 1, 2, 3, 4, and 5 years of followup were 2%, 4%, 7%, 19%, and 19%, respectively. Most patients (77%) experienced some improvement such as disappearance or decrease of bloody stool during hospitalization. The short- and long-term PBD scores after the hospitalization were higher than baseline PBD scores. Conclusion: Relapse rates after educational hospitalization providing a PBD were far lower than those reported with medication. Educational hospitalization is effective at inducing habitual dietary changes. [ABSTRACT FROM AUTHOR]

Spin-orbit torque (SOT)-induced magnetization switching in Co/Pt multilayer structures with a Pt buffer layer is studied aiming to realize SOT-magnetic random access memory (MRAM) devices with high thermal stability. Current-induced magnetization switching and effective fields are measured using Hall-bar devices. The switching efficiency, defined as a ratio of the areal anisotropy energy density to switching current density, increases with increasing the number of Co/Pt stacks. This trend is in accordance with the stacking number dependence of effective fields per unit current density. The effective spin-Hall angle of the Pt buffer layer for the sample with multiple Co/Pt stacks is significantly larger than that of Pt previously reported, suggesting a generation of SOT in Co/Pt multilayers. These results indicate that Co/Pt multilayers are promising for SOT-MRAM devices possessing high thermal stability and small switching current. [ABSTRACT FROM AUTHOR]

Background: Approximately 30% of patients with Crohn disease (CD) are unresponsive to biologies. No previous study has focused on a plant-based diet in an induction phase of CD treatment. Objective: To investigate the remission rate of infliximab combined with a plant-based diet as first-line (IPF) therapy for CD. Methods: This was a prospective single-group trial conducted at tertiary hospitals. Subjects included consecutive adults with a new diagnosis (n = 26), children with a new diagnosis (n = 11), and relapsing adults (n = 9) with CD who were naive to treatment with biologics. Patients were admitted and administered a standard induction therapy with infliximab (5 mg/kg; 3 infusions at 0, 2, and 6 weeks). Additionally, they received a lacto-ovo-semivegetarian diet. The primary end point was remission, defined as the disappearance of active CD symptoms at week 6. Secondary end points were Crohn Disease Activity Index (CDAI) score, C-reactive protein (CRP) concentration, and mucosal healing. Results: Two adults with a new diagnosis were withdrawn from the treatment protocol because of intestinal obstruction. The remission rates by the intention-to-treat and per-protocol analyses were 96% (44/46) and 100% (44/44), respectively. Mean CDAI score (314) on admission decreased to 63 at week 6 (p < 0.0001). Mean CRP level on admission (5.3 mg/dL) decreased to 0.2 (p < 0.0001). Mucosal healing was achieved in 46% (19/41) of cases. Conclusion: IPF therapy can induce remission in most patients with CD who are naive to biologics regardless of age or whether they have a new diagnosis or relapse. (The study ID number is UMIN000019061, UMIN000020335: Registration at www. umin.ac.jp). [ABSTRACT FROM AUTHOR]

Studies of magnetization dynamics have incessantly facilitated the discovery of fundamentally novel physical phenomena, making steady headway in the development of magnetic and spintronics devices. The dynamics can be induced and detected electrically, offering new functionalities in advanced electronics at the nanoscale. However, its scattering mechanism is still disputed. Understanding the mechanism in thin films is especially important, because most spintronics devices are made from stacks of multilayers with nanometer thickness. The stacks are known to possess interfacial magnetic anisotropy, a central property for applications, whose influence on the dynamics remains unknown. Here, we investigate the impact of interfacial anisotropy by adopting CoFeB/MgO as a model system. Through systematic and complementary measurements of ferromagnetic resonance (FMR) on a series of thin films, we identify narrower FMR linewidths at higher temperatures. We explicitly rule out the temperature dependence of intrinsic damping as a possible cause, and it is also not expected from existing extrinsic scattering mechanisms for ferromagnets. We ascribe this observation to motional narrowing, an old concept so far neglected in the analyses of FMR spectra. The effect is confirmed to originate from interfacial anisotropy, impacting the practical technology of spin-based nanodevices up to room temperature. [ABSTRACT FROM AUTHOR]

Context: Plant-based diets (PBDs) are a healthy alternative to westernized diets. A semivegetarian diet, a PBD, has been shown to prevent a relapse in Crohn disease. However, there is no way to measure adherence to PBDs. Objective: To develop a simple way of evaluating adherence to a PBD for Japanese patients with inflammatory bowel disease (IBD). Design: PBD scores were assigned according to the frequency of consumption provided on a food-frequency questionnaire, obtained on hospitalization for 159 patients with ulcerative colitis and 70 patients with Crohn disease. Eight items considered to be preventive factors for IBD were scored positively, and 8 items considered to be IBD risk factors were scored negatively. The PBD score was calculated from the sum of plus and minus scores. Higher PBD scores indicated greater adherence to a PBD. The PBD scores were evaluated on hospitalization and 2 years after discharge for 22 patients with Crohn disease whose dietary pattern and prognosis were established. Main Outcome Measure: Plant-Based Diet score. Results: The PBD scores differed significantly, in descending order, by dietary type: pro-Japanese diet, mixed type, and pro-westernized diet (Wilcoxon/Kruskal-Wallis test). The PBD scores in the ulcerative colitis and Crohn disease groups were 10.9 ± 9.5 and 8.2 ± 8.2, respectively. For patients with Crohn disease, those with long-term remission and normal C-reactive protein concentration were significantly more likely to have PBD scores of 25 or greater than below 25 (χ²). Conclusion: The PBD score is a valid assessment of PBD dietary adherence. [ABSTRACT FROM AUTHOR]

We report experimentally on fine structure splitting (FSS) of various excitonic transitions in single GaAs island quantum dots, formed by a monolayer thickness fluctuation in the narrow GaAs/ AlGaAs quantum well, and embedded in an n-i-Schottky diode device. By applying a forward vertical electric field (F) between the top metallic contact and the sample substrate, we observed an in-plane polarization rotation of both the ground and the excited state excitons with increasing the electric field. The polarization rotations were accompanied with a strong decrease in the FSS of the ground as well as the excited state excitons with the field, until the FSS vanished as F approached 30 kV/cm. [ABSTRACT FROM AUTHOR]

We have investigated the redox reaction on the surface of Ta/CoFeB/MgO/CoFeB magnetic tunnel junction stack samples after annealing at 300, 350, and 400 °C for 1 h using angle-resolved X-ray photoelectron spectroscopy for precise analysis of the chemical bonding states. At a capping tantalum layer thickness of 1 nm, both the capping tantalum layer and the surface of the underneath CoFeB layer in the as-deposited stack sample were naturally oxidized. By comparison of the Co 2p and Fe 2p spectra among the as-deposited and annealed samples, reduction of the naturally oxidized cobalt and iron atoms occurred on the surface of the CoFeB layer. The reduction reaction was more significant at higher annealing temperature. Oxidized cobalt and iron were reduced by boron atoms that diffused toward the surface of the top CoFeB layer. A single CoFeB layer was prepared on SiO2, and a confirmatory evidence of the redox reaction with boron diffusion was obtained by angle-resolved X-ray photoelectron spectroscopy analysis of the naturally oxidized surface of the CoFeB single layer after annealing. The redox reaction is theoretically reasonable based on the Ellingham diagram. [ABSTRACT FROM AUTHOR]

We measure homodyne-detected ferromagnetic resonance (FMR) induced by the electric-field effect in a CoFeB/MgO/CoFeB magnetic tunnel junction (MTJ) with perpendicular magnetic easy axis under dc bias voltages up to 0.1V. From the bias dependence of the resonant frequency, we find that the first order perpendicular magnetic anisotropy is modulated by the applied electric field, whereas the second order component is virtually independent of the electric field. The lineshapes of the FMR spectra are bias dependent, which are explained by the combination of electric-field effect and reflection of the bias voltage from the MTJ. [ABSTRACT FROM AUTHOR]

We study the spin and orbital magnetic moments in Ta/Co0.4Fe0.4B0.2/MgO by x-ray magnetic circular dichroism measurements as well as first-principles calculations, in order to clarify the origin of the perpendicular magnetic anisotropy. Both experimental and theoretical results show that orbital magnetic moment of Fe is more anisotropic than that of Co with respect to the magnetization direction. The anisotropy is larger for thinner CoFeB, indicating that Fe atoms at the interface with MgO contribute more than Co to the observed perpendicular magnetic anisotropy. [ABSTRACT FROM AUTHOR]

We grow Li codoped (Ga,Mn)As layers with nominal Mn composition up to 0.15 by molecular beam epitaxy. The layers before and after annealing are characterized by x-ray diffraction, transport, magnetization, and ferromagnetic resonance measurements. The codoping with Li reduces the lattice constant and electrical resistivity of (Ga,Mn)As after annealing. We find that (Ga,Mn)As:Li takes similar Curie temperature to that of (Ga,Mn)As, but with pronounced magnetic moments and in-plane magnetic anisotropy, indicating that the Li codoping has nontrivial effects on the magnetic properties of (Ga,Mn)As. [ABSTRACT FROM AUTHOR]

We evaluate the temperature dependence of in-plane magnetic anisotropy and anisotropic magnetoresistance (AMR) in (Ga,Mn)As codoped with Li by magnetotransport measurements. We find that the signs of in-plane uniaxial anisotropy and AMR change at the same temperature of ~75 K, and that the sign of planar Hall effect does not depend on temperature. [ABSTRACT FROM AUTHOR]

We study a growth technique of non-collinear antiferromagnetic Mn3Sn thin films deposited by sputtering with various substrates and underlayers. The relation between their crystal structure and magnetic/transport properties is also investigated. We achieve the formation of epitaxial films with both C-plane and M-plane orientations, whose Kagome lattices are parallel and perpendicular to the plane, respectively. Transverse resistivity originating from the anomalous Hall effect shows different trends reflecting the Kagome lattice orientation of each stack. The established technique and findings offer a platform to study functional devices utilizing the unconventional physical properties of non-collinear antiferromagnets with controlled Kagome lattice orientation. [ABSTRACT FROM AUTHOR]

In recent years, there has been an increasing need for dedicated devices that act as components of the brain for use in non-von Neumann-based architectures known as artificial neural networks (ANNs). Furthermore, to transition from the large, power-consuming supercomputer paradigm used to complete brain like tasks, such as pattern recognition, to a “wearable” edge-computing-based artificial intelligence (AI) paradigm, compact and efficient hardware is required. In this report, we describe one such approach towards hardware-based ANNs using recently reported spintronics technology. We give a systematic explanation on a procedure of an ANN-based associative memory operation using spin–orbit torque-controlled devices. On the basis of previously obtained results, we then elaborate on the specific roles and requirements of spintronics devices in the demonstration system. We also describe several challenges regarding efficient and reliable operation of the devices that is clarified by additional measurements of endurance properties of the device as a function of operation current. The results indicate that limitation of the maximum operation current to prevent the decay of device properties provides negligible device-to-device variation after hundreds of iterations, allowing for a reliable associative memory operation. [ABSTRACT FROM AUTHOR]

We investigate free-layer size D dependence of effective anisotropy field in nanoscale CoFeB/MgO magnetic tunnel junctions by homodyne-detected ferromagnetic resonance. The effective anisotropy field monotonically increases with decreasing D for a device with the reference-layer size much larger than the free-layer size. In contrast, does not increase in a monotonic manner for a device with the reference-layer size comparable to the free-layer size. We reveal that the difference can be explained by the variation of the anisotropy field in the vicinity of the device edge. [ABSTRACT FROM AUTHOR]

We investigate the energy barrier E that determines the thermal stability factor Δ, of CoFeB/MgO magnetic tunnel junctions (MTJs) with a perpendicular easy axis by retention time measurement as a function of temperature T and junction diameter D. E decreases with increasing T for all the studied MTJs. The temperature at which any particular value of E is obtained tends to decrease with decreasing D, indicating that the magnetization reversal in the MTJs is described by reversal models other than the nucleation model. We find that the temperature dependence of E correlates with that of spontaneous magnetization through the power law scaling relationship, which enables us to determine Δ at temperatures different from those used in the retention time measurement. [ABSTRACT FROM AUTHOR]

We study spin–orbit torque (SOT) switching in W/CoFeB/MgO structures with various dot sizes (120–3500 nm) using pulsed current of various widths τ (800 ps–100 ms) to examine the time and spatial evolution of magnetization switching. We show that the switching behavior and the resultant threshold switching current density Jth strongly depend on device size and pulse width. The switching mode in a 3500 nm dot device changes from probabilistic switching to reproducible partial switching as τ decreases. At τ = 800 ps, Jth becomes more than 3 times larger than that in the long-pulse regime. A decrease in dot size to 700 nm does not significantly change the switching characteristics, suggesting that domain-wall propagation among the nucleated multiple domains governs switching. In contrast, devices with further reduced size (120 nm) show normal full switching with increasing probability with current and insignificant dependence of Jth on τ, indicating that nucleation governs switching. [ABSTRACT FROM AUTHOR]

We investigate the temperature dependence of ferromagnetic resonance spectra of permalloy (Py: Ni0.80Fe0.20) on (Bi1−xSbx)2Te3 with x = 0–1. Smaller resonance fields and broader linewidths are observed for Py/(Bi,Sb)2Te3 than those for Py/substrate below ∼40 K. The result indicates the presence of the coupling as well as spin pumping at the interface between Py and (Bi,Sb)2Te3. [ABSTRACT FROM AUTHOR]

We investigate the electric-field effect on the magnetic anisotropy in perpendicularly magnetized Pt/Co/Pd/MgO structures deposited on GaAs and Si substrates as a function of temperature. An electric field is applied to the Pd surface through a 2-nm-thick insulating MgO layer by forming an electric double layer using an ionic liquid. We find that the electric-field dependence of the anisotropy is similar but clearly different between the two samples at low temperatures. The difference is expected to be related to the difference in the internal strain of the two structures. [ABSTRACT FROM AUTHOR]

We report on the molecular beam epitaxy and properties of a magnetic topological insulator (TI): Cr-doped Sb2Te3. Composition analysis reveals that Cr replaces Sb, and X-ray diffraction confirms that a single-phase textured crystal structure can be obtained for (CrxSb1−x)2Te3 with x up to 0.44. A further increase in x results in phase separation or precipitates in the material. The Curie temperature TC increases with x up to 0.44 and reaches 250 K, which is the highest TC observed thus far in magnetically doped TIs. [ABSTRACT FROM AUTHOR]

We investigate the magnetic properties of Fe100−xVx/MgO-based structures with a V composition x up to 20 at. %. The introduction of V results in the reduction of spontaneous magnetization, the damping constant, and both interfacial and bulk perpendicular magnetic anisotropies. However, the insertion of thin Fe layers at the FeV/MgO interfaces results in an effective perpendicular magnetic anisotropy as large as that of Fe/MgO. The result shows potential for lowering the threshold current for magnetization switching in FeV/MgO-based magnetic tunnel junctions, while maintaining a thermal stability factor similar to that in Fe/MgO-based junctions. [ABSTRACT FROM AUTHOR]

The influences of various types of high-energy heavy-ion radiation on 10-nm-scale CoFeB–MgO magnetic tunnel junctions with a perpendicular easy axis have been investigated. In addition to possible latent damage, which has already been pointed out in previous studies, high-energy heavy-ion bombardments demonstrated that the magnetic tunnel junctions may exhibit clear flips between their high- and low-resistance states designed for a digital bit 1 or 0. It was also demonstrated that flipped magnetic tunnel junctions still may provide proper memory functions such as read, write, and hold capabilities. These two findings proved that high-energy heavy ions can produce recoverable bit flips in magnetic tunnel junctions, i.e., soft errors. Data analyses suggested that the resistance flips stem from magnetization reversals of the ferromagnetic layers and that each of them is caused by a single strike of heavy ions. It was concurrently found that an ion strike does not always result in a flip, suggesting a stochastic process behind the flip. Experimental data also showed that the flip phenomenon is dependent on the device and heavy-ion characteristics. Among them, the diameter of the device and the linear energy transfer of the heavy ions were revealed as the key parameters. From their dependences, the physical mechanism behind the flip was discussed. It is likely that a 10-nm-scale ferromagnetic disk loses its magnetization due to a local temperature increase induced by a single strike of heavy ions; this demagnetization is followed by a cooling period associated with a possible stochastic recovery process. On the basis of this hypothesis, a simple analytical model was developed, and it was found that the model accounts for the results reasonably well. This model also predicted that magnetic tunnel junctions provide sufficiently high soft-error reliability for use in space, highlighting their advantage over their counterpart conventional semiconductor memories. [ABSTRACT FROM AUTHOR]

This work represents the first-ever investigation of the effects of fast neutron exposure on the perpendicular-anisotropy CoFeB–MgO magnetic tunnel junctions (p-MTJs) with practical junction diameters (D) between 46 and 64 nm. In this study, 461 p-MTJs, each with a tunnel magnetoresistance (TMR) ratio above 90%, were irradiated with fast neutrons at a total 1 MeV equivalent fluence of 3.79 × 1012 cm−2, corresponding to 1.90 × 1011 h irradiation with fast atmospheric neutrons (20 cm−2 h−1), without applying a bias voltage. Following irradiation, there were no changes in the properties of these devices, such as their resistance versus magnetic field curves, resistance values in the parallel and anti-parallel states, or TMR ratios, regardless of the neutron fluence. On the basis of these data, the nuclear reactions that occur under the specific experimental neutron irradiation conditions employed in this work are discussed. [ABSTRACT FROM AUTHOR]

We investigate the annealing temperature dependence of the magnetic properties of CoFeB/MgO stacks with different buffer materials (Mo, Ta, and W). For Mo and W, bcc-crystalline and amorphous-like films are prepared by changing the deposition conditions. A relatively small saturation magnetization is maintained after annealing up to 400 °C for the samples with bcc-W, bcc-Mo, and amorphous-like Mo buffers. A small variation in magnetic dead layer thickness with annealing is observed for the samples with bcc-crystalline buffer layers. The interfacial anisotropy is found to mainly depend on the element of the buffer layer used regardless of its crystalline structure, and is larger for the samples with W and Mo buffers than those with Ta buffer. The sample with bcc-Mo buffer shows the highest robustness against annealing among the studied systems. We give a systematic picture based on the thermochemistry that can reasonably explain the observed buffer layer dependence of the variations in magnetic properties with annealing. [ABSTRACT FROM AUTHOR]

Utilizing spintronics-based nonvolatile memories in integrated circuits offers a promising approach to realize ultralow-power and high-performance electronics. While two-terminal devices with spin-transfer torque switching have been extensively developed nowadays, there has been a growing interest in devices with a three-terminal structure. Of primary importance for applications is the efficient manipulation of magnetization, corresponding to information writing, in nanoscale devices. Here we review the studies of current-induced domain wall motion and spin–orbit torque-induced switching, which can be applied to the write operation of nanoscale three-terminal spintronics devices. For domain wall motion, the size dependence of device properties down to less than 20 nm will be shown and the underlying mechanism behind the results will be discussed. For spin–orbit torque-induced switching, factors governing the threshold current density and strategies to reduce it will be discussed. A proof-of-concept demonstration of artificial intelligence using an analog spin–orbit torque device will also be reviewed. [ABSTRACT FROM AUTHOR]

The electric-field effect on magnetic anisotropy provides a low-energy scheme for magnetization switching in magnetic tunnel junctions. We review our recent works on the electric-field-induced magnetization switching in CoFeB/MgO-based magnetic tunnel junctions. We show that the switching with a higher speed and a lower energy than the spin-transfer switching can be realized using the electric-field effect. The increase of the electric-field modulation ratio is expected to result in a marked reduction of the switching energy as well as in the improvement of the switching reliability for magnetic tunnel junctions with a high thermal stability factor. Further study is necessary to improve the modulation ratio. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junctions with a perpendicular easy axis (p-MTJs) have been intensively developed since CoFeB/MgO p-MTJs were shown to have high potential in satisfying major requirements for use in practical applications. CoFeB/MgO-based p-MTJs are becoming the de facto standard in spin-transfer-torque magnetoresistive random access memory and spintronics-based very large scale integrated circuits. In this paper, we review, based on our efforts, the properties of standard CoFeB/MgO based p-MTJs as well as p-MTJs using high-anisotropy Co-based multilayers combined with the CoFeB/MgO system at a junction diameter of less than 20 nm. [ABSTRACT FROM AUTHOR]

A magnetic-tunnel-junction (MTJ)-based video coding hardware with an MTJ-write-error-rate relaxation scheme as well as a nonvolatile storage capacity reduction technique is designed and fabricated in a 90 nm MOS and 75 nm perpendicular MTJ process. The proposed MTJ-oriented dynamic error masking scheme suppresses the effect of write operation errors on the operation result of LSI, which results in the increase in an acceptable MTJ write error rate up to 7.8 times with less than 6% area overhead, while achieving 79% power reduction compared with that of the static-random-access-memory-based one. [ABSTRACT FROM AUTHOR]

A high-density nonvolatile associative memory (NV-AM) based on spin transfer torque magnetoresistive random access memory (STT-MRAM), which achieves highly concurrent and ultralow-power nearest neighbor search with full adaptivity of the template data format, has been proposed and fabricated using the 90 nm CMOS/70 nm perpendicular-magnetic-tunnel-junction hybrid process. A truly compact current-mode circuitry is developed to realize flexibly controllable and high-parallel similarity evaluation, which makes the NV-AM adaptable to any dimensionality and component-bit of template data. A compact dual-stage time-domain minimum searching circuit is also developed, which can freely extend the system for more template data by connecting multiple NM-AM cores without additional circuits for integrated processing. Both the embedded STT-MRAM module and the computing circuit modules in this NV-AM chip are synchronously power-gated to completely eliminate standby power and maximally reduce operation power by only activating the currently accessed circuit blocks. The operations of a prototype chip at 40 MHz are demonstrated by measurement. The average operation power is only 130 µW, and the circuit density is less than 11 µm2/bit. Compared with the latest conventional works in both volatile and nonvolatile approaches, more than 31.3% circuit area reductions and 99.2% power improvements are achieved, respectively. Further power performance analyses are discussed, which verify the special superiority of the proposed NV-AM in low-power and large-memory-based VLSIs. [ABSTRACT FROM AUTHOR]

We demonstrate associative memory operations reminiscent of the brain using nonvolatile spintronics devices. Antiferromagnet–ferromagnet bilayer-based Hall devices, which show analogue-like spin–orbit torque switching under zero magnetic fields and behave as artificial synapses, are used. An artificial neural network is used to associate memorized patterns from their noisy versions. We develop a network consisting of a field-programmable gate array and 36 spin–orbit torque devices. An effect of learning on associative memory operations is successfully confirmed for several 3 × 3-block patterns. A discussion on the present approach for realizing spintronics-based artificial intelligence is given. [ABSTRACT FROM AUTHOR]

We investigate the damping constant of a free layer with a perpendicular magnetic easy axis in nanoscale CoFeB/MgO magnetic tunnel junctions (MTJs) with a reference layer with an in-plane easy direction. The built-in noncollinear magnetization configuration in the MTJs allows us to measure homodyne-detected ferromagnetic resonance without tilting the magnetization direction of the free layer from the device normal. The damping constants determined from the spectral linewidths after the subtraction of the inhomogeneous broadening are nearly independent of the device diameter ranging from 70 to 100 nm, and take values similar to those reported for blanket CoFeB films. [ABSTRACT FROM AUTHOR]