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Abstract In spin wave (SW) devices, the modulation of SWs for computational units is necessary, imposing extremely high demands on material systems. In this study, high‐quality epitaxial‐grown spinel γ‐Fe2O3 thin films on conductive Nb‐doped SrTiO3 substrates, achieving fast‐speed, high‐frequency, and long‐distance SW propagation in this ferrimagnetic material, are developed. A novel two‐step film growth technique using pulsed laser deposition is proposed and optimized, and the damping constant, exchange stiffness, and anisotropies of γ‐Fe2O3 are determined. Compared to reported semiconductor magnetic materials, these epitaxial‐grown γ‐Fe2O3 thin films exhibit a significantly lower damping constant of 10−2, representing a substantial advancement. Using finite‐difference calculations, SW propagation is simulated, and vital information on transmission distance and dispersion curves is obtained. Experimental results show excellent agreement with these simulations. By applying a voltage to both sides of the conducting substrate, current across the film and SW device, resulting in the frequency shift of the SWs, is generated. These results demonstrate that high‐quality γ‐Fe2O3 films developed through the two‐step growth method can efficiently propagate SWs, offering possibilities for various modulation methods in SW‐based computing devices. This study positions spinel γ‐Fe2O3 as a promising ferrimagnetic candidate for future applications in efficient SW modulation within computational systems.

Magnetic tunnel junctions (MTJs) are considered strong candidates for constructing neuromorphic systems owing to their low power consumption and high integrability. However, research on MTJ-based local approximation network is still lacking. In this work, we propose an MTJ-based radial basis function (RBF) network and numerically investigate its time-series prediction capability. The results demonstrate that the MTJ-based RBF network can enhance its prediction performance by utilizing increased environmental temperatures, achieving performance better than traditional software artificial neural networks.

Abstract Gain‐dissipative Ising machines (GIMs) are annealers inspired by physical systems such as Ising spin glasses to solve combinatorial optimization problems. Compared to traditional quantum annealers, GIM is relatively easier to scale and can save on additional power consumption caused by low‐temperature cooling. However, traditional GIMs have a limited noise margin. Specifically, their normal operation requires ensuring that the noise intensity is lower than their saturation fixed point amplitude, which may result in increased power consumption to suppress noise‐induced spin state switching. To enhance the noise robustness of GIM, in this study a GIM based on a topologically defective lattice potential (TDLP) is proposed. Numerical simulations demonstrate that the TDLP‐based GIM can accurately simulate the bifurcation spin evolution in the Ising model. Furthermore, through the MAXCUT benchmark based on G‐set graphs, the optimal performance of TDLP‐based GIM is shown to surpass that of traditional GIMs. Additionally, the proposed TDLP‐based GIM successfully solves the MAXCUT benchmark and domain clustering dynamics benchmark based on G‐set graphs when the noise intensity exceeds its saturation fixed‐point amplitude. This indicates that the proposed system provides a promising architecture for breaking the small noise constraints required by traditional GIMs.

Accurately detecting the depolarization QRS complex in the ventricles is a fundamental requirement for cardiovascular disease detection using electrocardiography (ECG). In contrast to traditional signal enhancement algorithms, emerging neural network approaches have shown promise for QRS detection because of their generalizability on complex data. However, the inevitable noise present during ECG recording leads to a decrease in the performance of neural networks. To enhance the robustness and performance of neural network-based QRS detectors, we propose a simulated degeneration unit (SDU)-assisted convolutional neural network (CNN). An SDU simulates the physical degeneration process of interfering optical pulses, which can effectively suppress in-band noise. Through comprehensive performance evaluations on three open-source databases, the SDU-enhanced CNN-based approach demonstrated better performance in detecting QRS complexes than other recently reported QRS detectors. Furthermore, real-world noise injection tests indicate that the optimal noise robustness boundary for the CNN equipped with SDU is 167–300% higher than that for the CNN without SDU.

Abstract Reservoir computing is a brain heuristic computing paradigm that can complete training at a high speed. The learning performance of a reservoir computing system relies on its nonlinearity and short-term memory ability. As physical implementation, spintronic reservoir computing has attracted considerable attention because of its low power consumption and small size. However, few studies have focused on developing the short-term memory ability of the material itself in spintronics reservoir computing. Among various magnetic materials, spin glass is known to exhibit slow magnetic relaxation that has the potential to offer the short-term memory capability. In this research, we have quantitatively investigated the short-term memory capability of spin cluster glass based on the prevalent benchmark. The results reveal that the magnetization relaxation of Co, Si-substituted Lu3Fe5O12 with spin glass behavior can provide higher short-term memory capacity than ferrimagnetic material without substitution. Therefore, materials with spin glass behavior can be considered as potential candidates for constructing next-generation spintronic reservoir computing with better performance.

Abstract Spin waves (SWs), an ultra-low power magnetic excitation in ferro or antiferromagnetic media, have tremendous potential as transport less data carriers for post-CMOS technology using their wave interference properties. The concept of magnon interference originates from optical interference, resulting in a historical taboo of maintaining an identical wavevector for magnon interference-based devices. This makes the attainment of on-chip design reconfigurability challenging owing to the difficulty in phase tuning via external fields. Breaking the taboo, this study explores a novel technique to systematically control magnon interference using asymmetric wavevectors from two different SW modes (magnetostatic surface SWs and backward volume magnetostatic SWs) in a microstructured yttrium iron garnet crossbar. Using this system, we demonstrate phase reconfigurability in the interference pattern by modulating the thermal landscape, modifying the dispersion of the interfering SW modes. Thus, we manifest that such a tunable interference can be used to implement reconfigurable logic gates operating between the XNOR and XOR modes by using symmetric and asymmetric interference, respectively.

The interface between perovskite-oxide SrTiO3 and other oxides realizes efficient spin-to-charge current conversion; however, the typically insulating oxides hinder the propagation of spin-currents. Here the authors achieve a record efficiency by replacing an oxide insulator with a strongly-correlated polar metal.

Logical stochastic resonance (LSR) system is a physical system capable of performing robust reconfigurable logical operations in the presence of background noise using specific nonlinearities. Traditional LSR systems are typically based on polynomial nonlinearities, which make them suitable for implementation by electronic components. However, there has been little research on LSR systems based on hyperbolic nonlinearities which have the potential to be realized directly using the physical properties of materials. Inspired by the kink-bearing potential related to phonon nonlinear excitation, we propose an LSR system based on a hyperbolic one-site lattice (HOL) for the first time in this study. The performance of the HOL-based LSR (HOL-LSR) system is investigated under both noise-free and noisy conditions. Moreover, assisted by a bionic optimizer, we compare the performance of the proposed HOL-LSR and traditional quadstable LSR (QLSR) system under the influence of Gaussian white noise and Lévy pulse. The results demonstrate the existence of parameter-induced LSR effects in the HOL-LSR system. In addition, with only Gaussian white noise, the performance of the HOL-LSR and QLSR systems is comparable. However, when the background noise contains pulse components, the robustness of the HOL-LSR system is significantly stronger than that of the QLSR system. These results prove the superiority of HOL-LSR system over traditional LSR and encourage the construction of LSR systems directly based on material with hyperbolic property.

Abstract Magnonics, an emerging research field that uses the quanta of spin waves as data carriers, has a potential to dominate the post-CMOS era owing to its intrinsic property of ultra-low power operation. Spin waves can be manipulated by a wide range of parameters; thus, they are suitable for sensing applications in a wide range of physical fields. In this study, we designed a highly sensitive, simple structure, and ultra-low power magnetic sensor using a simple CoFeB/Y3Fe5O12 bilayer structure. We demonstrated that the CoFeB/Y3Fe5O12 bilayer structure can create a sharp rejection band in its spin-wave transmission spectra. The lowest point of this strong rejection band allows the detection of a small frequency shift owing to the external magnetic field variation. Experimental observations revealed that such a bilayer magnetic sensor exhibits 20 MHz frequency shifts upon the application of an external magnetic field of 0.5 mT. Considering the lowest full width half maximum, which is about 2 MHz, a sensitivity of 10–2 mT order can be experimentally achieved. Furthermore, the higher sensitivity in the order of 10–6 T (µT) has been demonstrated using the sharp edge of the rejection band of the CoFeB/Y3Fe5O12 bilayer device. A Y-shaped spin waves interference device with two input arms consisting of CoFeB/Y3Fe5O12 and Y3Fe5O12 has been theoretically investigated. We proposed that such a structure can demonstrate a magnetic sensitivity in the range of $${10}^{-9}$$ 10 - 9 T (nT) at room temperature. The sensitivity of the sensor can be further enhanced by tuning the width of the CoFeB metal stripe.

To mimic the human olfactory system, an electronic nose (E-nose, also known as artificial olfactory) has been proposed based on a multiple gas sensor array and a pattern recognition algorithm. Detection of volatile organic components (VOCs) has many potential applications in breath analysis, food quality estimation, and indoor and outdoor air quality monitoring, etc. In this study, a facile single-needle electrospinning technology was applied to develop the four different semiconductor metal oxide (MOS) nanofibers sensor arrays (SnO2, CuO, In2O3 and ZnO, respectively). The array shows a smooth surface and constant diameter of nanofiber (average of 150 nm) resulting in high sensitivity to multiple target analyte gases. Five human health related VOCs gases were measured by fabricated E-nose and different response patterns were obtained from four MOS nanofibers sensors. Combined with feature extraction from the response curves, a principal component analysis (PCA) algorithm was applied to reduce the dimension of feature matrix, Thus, the fabricated E-nose system successfully discriminated five different VOCs gases. Real-time and non-invasive gas monitoring by E-nose is very promising for application in human health monitoring, food monitoring, and other fields.

Objectives To examine the national, 6-year trends in in-hospital clinical outcomes of patients with subarachnoid haemorrhage (SAH) who underwent clipping or coiling and the prognostic influence of temporal trends in the Comprehensive Stroke Center (CSC) capabilities on patient outcomes in Japan.Design Retrospective study.Setting Six hundred and thirty-one primary care institutions in Japan.Participants Forty-five thousand and eleven patients with SAH who were urgently hospitalised, identified using the J-ASPECT Diagnosis Procedure Combination database.Primary and secondary outcome measures Annual number of patients with SAH who remained untreated, or who received clipping or coiling, in-hospital mortality and poor functional outcomes (modified Rankin Scale: 3–6) at discharge. Each CSC was assessed using a validated scoring system (CSC score: 1–25 points).Results In the overall cohort, in-hospital mortality decreased (year for trend, OR (95% CI): 0.97 (0.96 to 0.99)), while the proportion of poor functional outcomes remained unchanged (1.00 (0.98 to 1.02)). The proportion of patients who underwent clipping gradually decreased from 46.6% to 38.5%, while that of those who received coiling and those left untreated gradually increased from 16.9% to 22.6% and 35.4% to 38%, respectively. In-hospital mortality of coiled (0.94 (0.89 to 0.98)) and untreated (0.93 (0.90 to 0.96)) patients decreased, whereas that of clipped patients remained stable. CSC score improvement was associated with increased use of coiling (per 1-point increase, 1.14 (1.08 to 1.20)) but not with short-term patient outcomes regardless of treatment modality.Conclusions The 6-year trends indicated lower in-hospital mortality for patients with SAH (attributable to better outcomes), increased use of coiling and multidisciplinary care for untreated patients. Further increasing CSC capabilities may improve overall outcomes, mainly by increasing the use of coiling. Additional studies are necessary to determine the effect of confounders such as aneurysm complexity on outcomes of clipped patients in the modern endovascular era.

Rare-earth iron garnets are ferrimagnetic insulators commercially known for their large magneto-optical effect. Here, strain-gradient engineering is used to induce flexoelectricity in Sm3Fe5O12 films, achieving simultaneous remanent dielectric polarization and magnetization at room temperature.

Logical stochastic resonance (LSR) is a paradigm to realize reconfigurable robust Boolean operations using specific nonlinearity in the presence of background noise. The stable-state number of the traditional LSR is less than four, which restricts its upper limit in the heavy noise floor. To further improve the noise robustness and output quality of LSR, we proposed quadstable nonlinearity based LSR system for the first time in this work. Using the parameters determined by the ant lion optimizer, we compare the performance of proposed quadstable LSR (QLSR) and traditional tristable LSR (TLSR) as reconfigurable logic gates in the heavy noise floor. The results show that in the heavy noise floor with noise intensity fluctuation, the maximum noise intensity that the QLSR can withstand is significantly higher than the that of TLSR. When the heavy noise floor contains pulses, the pulse robustness of QLSR and TLSR is comparable. Nevertheless, the quantitative indexes reveal that larger stable-state numbers endow the QLSR a stronger ability to extract noise energy for enhancing logic information; thus, the output quality of QLSR is better than that of TLSR.

We have examined impacts of gate insulator (Al2O3 or HfO2) and gate electrode (TiN or W) on electrical performance of ZnSnO/Si bilayer tunneling field-effect transistors (TFETs). It is found from the capacitance-voltage (C-V) characteristics that the W gate is effective to reduce the counter-clockwise hysteresis. Additionally, the optimal temperature of post-metallization annealing (PMA) is different for each gate stack, and this optimization is critically important for the high ON-state current (ION) and steep ON/OFF switching. The W/Al2O3/ZnSnO/Si bilayer TFET provides the hysteresis-free steep ON/OFF switching with the minimum sub-threshold swing (SS) of 65.4 mV/dec. and average SS of 72.0 mV/dec. in a gate-voltage swing of 0.3 V, which are 19% and 18% lower than the control TiN/Al2O3/ZnSnO/Si bilayer TFET. When the gate stack is replaced by W/HfO2/Al2O3, the TFET exhibits less steep ON/OFF switching in spite of thinning capacitance equivalent thickness (CET) from 5.9 and 2.3 nm. These results indicate the importance of improvement in the gate stack quality on the sub-threshold characteristics of the bilayer TFETs.

Thin films of BaFe1-xMxO3 (M = Hf, Zr, and Ce; 0.0 ≤ x ≤ 0.75) were fabricated using pulsed laser deposition and their magnetic properties were investigated. X-ray diffraction analysis indicated that oxygen-deficient BaFeOx (x < 3.0) with a monoclinic structure was formed when the deposition was conducted using a non-substituted target (x = 0.0). The as-grown BaFeOx films were converted into fully oxidized BaFeO3 with a perovskite structure by low-temperature oxidation in an ozone atmosphere. In contrast, the as-deposited films of Hf, Zr, and Ce-substituted films exhibited a perovskite structure, and their crystallinity did not change after low-temperature ozone annealing. The magnetic transition temperature Tc of the BaFeO3 film was 115 K, whereas the substituted BaFeO3 films showed ferromagnetic behavior even at 300 K. These results can be attributed to the weakening of the antiferromagnetic super-exchange coupling among Fe ions owing to the lattice expansion in the substituted BaFeO3. In addition, the magnetization of the films was found to increase with the decreasing ionic ratio of Fe4+/Fe3+, suggesting that the inherent carrier-induced ferromagnetic interaction is dominant in the films.

Superparamagnetic tunnel junctions (SMTJs) are spintronic nanodevices that can oscillate spontaneously under the influence of thermal noise. Studies have proposed that SMTJs can be modeled as magnetic neurons by subjecting them to electrical Gaussian white noise and can be subsequently synchronized under subthreshold driving. Considering the non-Gaussian background noise in industrial applications, this study investigated the influence of levy noise on SMTJ subthreshold synchronization. The results revealed that levy noise with weak pulse characteristics can be used to promote the subthreshold synchronization of the SMTJs, whereas levy noise with enhanced pulse characteristics cannot be used. Under the same conditions, enhanced levy noise asymmetry is advantageous for achieving SMTJ synchronization under subthreshold driving.

We demonstrate improvement of electrical characteristics of a bilayer tunneling field effect transistor (TFET) composed of an n-type zinc-tin-oxide (ZnSnO) channel with superior thickness uniformity and a p-type Si source. Careful optimization of the deposition condition of the ZnSnO layer leads to the significant improvement of the thickness uniformity thanks to its amorphous structure. It is promising to reduce the average sub-threshold swing (S.S.) of the bilayer TFET. The average S.S. of the amorphous ZnSnO/Si TFET is 87 mV/dec. in a gate voltage swing of 0.3 V, which is lower by 30% than that of the poly-crystalline ZnO/Si TFET with the rough surface. The minimum S.S. value of 80 mV/dec. in the ZnSnO/Si TFET is similar to that in the ZnO/Si TFET. Additionally, the ZnSnO/Si TFET has realized the increase in on-state current (Ion) and the achieved Ion of 1.7 μA/μm is approximately 8 times higher than that of the ZnO/Si TFET. We also found that the ZnSnO/Si TFET shows the stronger temperature dependence of bothIon and S.S. than the ZnO/Si TFET. These differences in the electrical characteristics between ZnSnO and ZnO TFETs are discussed in terms of the amorphous and ploy-crystalline natures of the OS channels.

We present a comparison of the spin wave propagation in Au/Y3Fe5O12 and Pt/Y3Fe5O12 bilayers. Microwave technique with a co-planner waveguide arrangement was used to excite and detect the spin wave. We observed a suppression in the propagating spin wave intensity when a metal stripe is placed on the surface of Y3Fe5O12 in the spin wave propagation path due to the spin pumping from Y3Fe5O12 to nonmagnetic metal stripe. However, a significant difference in the suppression property was observed with the Au and Pt electrode layers, which cannot be explained by the enhancement of the damping constant induced by spin pumping alone. The significant suppression of the spin wave propagation in the Au/Y3Fe5O12 bilayer system is attributed to the spin backflow and two magnon scattering.

Abstract Understanding and controlling the interfacial magnetic properties of ferromagnetic thin films are crucial for spintronic device applications. However, using conventional magnetometry, it is difficult to detect them separately from the bulk properties. Here, by utilizing tunneling anisotropic magnetoresistance in a single-barrier heterostructure composed of La0.6Sr0.4MnO3 (LSMO)/LaAlO3 (LAO)/Nb-doped SrTiO3 (001), we reveal the presence of a peculiar strong two-fold magnetic anisotropy (MA) along the [110]c direction at the LSMO/LAO interface, which is not observed in bulk LSMO. This MA shows unknown behavior that the easy magnetization axis rotates by 90° at an energy of 0.2 eV below the Fermi level in LSMO. We attribute this phenomenon to the transition between the e g and t 2g bands at the LSMO interface. Our finding and approach to understanding the energy dependence of the MA demonstrate a new possibility of efficient control of the interfacial magnetic properties by controlling the band structures of oxide heterostructures.

Operation mechanisms and electrical characteristics of tunneling field-effect transistors (TFETs) employing a hetero tunneling junction by utilizing an n-type oxide-semiconductor (OS) and a p-type group-IV-semiconductor are comprehensibly analyzed. Gate-normal band-to-band tunneling (BTBT) has high potential for the superior TFET performance such as high on-state current and small sub-threshold swing (S.S.). Additionally, a hetero tunneling junction with type-II energy band alignment is promising to exponentially increase tunneling probability with keeping small off-state current. Therefore, in this study, we investigate the impact of key material and device parameters such as energy band alignment of source/channel regions and thickness of the OS channel layer or gate insulator based on technology computer aided design (TCAD) simulation. The gate-controlled uniform band bending along the source-drain direction realizes uniform BTBT in the entire region of the hetero tunneling junction. Also, the reduction of the tunneling barrier height, which is continuously controlled by the conduction band minimum of the OS-channel and the valence band maximum of the IV-source, is effective to increases on-state current and decrease S.S. value. On the other hand, the thicknesses of OS channel layer and gate insulator have strong influences on tunneling probability and threshold voltage. Therefore, the sub-threshold characteristics of TFETs are sensitive to non-uniformities in the tunneling junction such as channel thickness fluctuation and surface potential fluctuation at the metal-oxide-semiconductor (MOS) interfaces. These numerical analyses of the device operation are essentially important to understand the effects of key device parameters on the TFET performance and to realize the superior electrical performance.

We demonstrate efficient intrinsic spin-to-charge current conversion in a two-dimensional electron gas using an all-epitaxial single-crystal heterostructure of LaSrMnO_{3}/LaAlO_{3}/SrTiO_{3}, which can suppress spin scattering and give us an ideal environment to investigate intrinsic spin-charge conversion. With decreasing temperature to 20 K, the spin-to-charge conversion efficiency is drastically enhanced to +6.7nm. Our band-structure calculation well reproduces this behavior and predicts further enhancement by controlling the density and relaxation time of the carriers.

The optical excitation of NbO_{2} is known to induce a transient metallicity that partially recovers on a subpicosecond speed and only fully recovers after several nanoseconds. Here, through low-fluence pump-probe spectroscopy, the short-lived and long-lived components of NbO_{2}’s optically induced modulation are found to be linearly dependent on pump fluence in the low-fluence regime. Through an in-depth analysis, the short-lived and long-lived modulations are found to be caused by photocarrier-induced refractive index changes and photothermally induced changes in the lattice temperature of NbO_{2}, respectively, and not an insulator-metal transition.