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A one-dimensional charge-density wave (CDW) is driven to slide by a dc electric field, carrying an electric current. In an additional ac field with frequency ω ex , it is known that the sliding CDW can be synchronized to ω ex , leading to the occurrence of Shapiro steps in the I–V characteristics. Motivated by a recent experiment where ac fields with two frequencies ω ex and ω ex ′ are simultaneously applied, we theoretically investigate the effects of frequency mixing on the Shapiro-step formation. Based on the Fukuyama–Lee–Rice model, we show that in addition to the main steps induced by ω ex , satellite steps characterized by ω ex ′ emerge. It is also found that with increasing the ac-field strength for ω ex ′ , each step width first exhibits a damped oscillation as in the one-frequency case and then exhibits a non-monotonic behavior. The origin of these behaviors and the relevance to the associated experiment are also discussed. [ABSTRACT FROM AUTHOR]

Increasing the electric current from a single-electron source is a main challenge in an effort to establish the standard of the ampere defined by the fixed value of the elementary charge e and the operation frequency f. While the current scales with the frequency, due to an operation frequency limit for maintaining accurate single-electron transfer, parallelization of single-electron sources is expected to be a more practical solution to increase the generated electric current I = Nef , where N is the number of parallelized devices. One way to parallelize single-electron sources without increasing the complexity in device operation is to use a common gate. Such a scheme will require each device to have the same operation parameters for single-electron transfer. In order to investigate this possibility, we study the statistics for operation gate voltages using single-electron sources embedded in a multiplexer circuit. The multiplexer circuit allows us to measure 64 single-electron sources individually in a single cooldown. We also demonstrate the parallelization of three single-electron sources and observe the generated current enhanced by a factor of three. [ABSTRACT FROM AUTHOR]

Magnon, the quanta of spin waves, can serve as an efficient spin information carrier for memory and logic applications, with the advantages of the Joule-heating free induced low power-dissipation property and the phase-coherent induced quantum phenomena. In analogy to spintronics, magnonics focuses on the excitation, detection, and manipulation of magnons (spin waves). In recent years, with the development of nanotechnology, abundant magnonic phenomena emerge in the nanoscale, such as the spin Seebeck effect, magnon-mediated electric current drag effect, magnon valve effect, magnon junction effect, magnon resonant transimission, magnon transfer torque, spin wave propagation, subterahertz spin wave excitation, magnon Bose–Einstein condensation, and so on. Here, we review the recent progresses in magnonics from physics, materials to devices, shedding light on the future directions for magnonics. [ABSTRACT FROM AUTHOR]

A series of single crystal Sr2Ir1–xRuxO4 (0 ≤ x ≤ 0.55) have been synthesized, and their physical properties have been investigated. Ru-substitution at Ir-site can drastically reduce the resistivity, which is accompanied by serious suppression of the long range antiferromagnetic order. With the application of electric current, remarkable electroresistance exceeding 90% is obtained at x ∼ 0.2, which may contain significant contribution from the strong magnetic competitions. Interestingly, insulator–metal transition driven by electric current is observed (e.g., below 100 K), which can be ascribed to the lattice modulation. The findings indicate that the electric current can be an efficient route to tune the physical properties of the Jeff = 1/2 Mott insulator. [ABSTRACT FROM AUTHOR]

A series of single crystal Sr2Ir1–xRuxO4 (0 ≤ x ≤ 0.55) have been synthesized, and their physical properties have been investigated. Ru-substitution at Ir-site can drastically reduce the resistivity, which is accompanied by serious suppression of the long range antiferromagnetic order. With the application of electric current, remarkable electroresistance exceeding 90% is obtained at x ∼ 0.2, which may contain significant contribution from the strong magnetic competitions. Interestingly, insulator–metal transition driven by electric current is observed (e.g., below 100 K), which can be ascribed to the lattice modulation. The findings indicate that the electric current can be an efficient route to tune the physical properties of the Jeff = 1/2 Mott insulator. [ABSTRACT FROM AUTHOR]

The spin current can be generated by passing an electric current through a heavy metal. The spin current generation depends on the spin Hall angle (θsh) of the material. To manipulate the effective θsh, a thin layer of Au has been introduced at the bottom Pt/Co and the top Co/Pt interfaces in Ta/Pt/Co/Pt based perpendicularly magnetic anisotropy systems, and current-induced magnetization reversal of Co has been studied to estimate Jc. The introduction of the Au layer at the top Co/Pt interface (Ta/Pt/Co/Au/Pt) did not produce any significant reduction in the Jc. However, a significant reduction of Jc (∼ 34 %) has been observed, while the Au layer has been deposited at the bottom Pt/Co interface (Ta/Pt/Au/Co/Pt), indicating an enhancement in the value of θsh. We also performed a micromagnetic simulation to understand the qualitative change of the θsh. Micromagnetic simulation suggested that the θsh becomes 0.07 in Ta/Pt/Au/Co/Pt multilayer compared to θ s h = 0.05 of the Ta/Pt/Co/Pt system. Pt/Co/Au/Co/Au exhibits a reduction in Jc up to ∼ 30 % and corresponds to θ s h = 0.09. A Ta capping layer has been introduced to inject more spin current into the Co layer since Pt and Ta have opposite spin Hall angles. The Jc lowers up to ∼ 58 % in Ta/Pt/Au/Co/Pt/Ta multilayer, corresponding to θ s h = 0.23. We also achieved field-free switching at J c = 1.55 × 10 11 by depositing an in-plane magnetized layer of Co in Ta/Pt/Au/Co/Pt/Ta/Co/Pt multilayer. [ABSTRACT FROM AUTHOR]

Light transition metals have recently emerged as a sustainable material class for efficient spin–charge interconversion. We report measurements of current-induced spin–orbit torques generated by Ni1−xCux alloys in perpendicularly magnetized ferrimagnetic Gd/Fe multilayers. We show that the spin–orbit torque efficiency of Ni1−xCux increases with the Ni/Cu atomic ratio, reaching values comparable to those of Pt for Ni55Cu45. Furthermore, we demonstrate magnetization switching of a 20-nm-thick Gd/Fe multilayer with a threshold current that decreases with increasing Ni concentration, similar to the spin–orbit torque efficiency. Our findings show that Ni1−x Cu x − based magnetic heterostructures allow for efficient control of the magnetization by electric currents. [ABSTRACT FROM AUTHOR]

The phenomenon of chirality-induced spin selectivity (CISS), where chiral organic molecules enable the selective transmission of electrons spin-polarized along the direction of electric current, has been studied for nearly two decades. Despite its technological relevance, CISS is not fully understood. Recent studies have expanded the concept of spin selectivity to chiral inorganic crystals, offering promise for magnet-free spintronics and other applications. This Perspective reviews recent developments on spin selectivity in non-magnetic solid-state materials, whereby chirality-dependent charge-to-spin conversion is responsible for transforming electric currents into spin signals, and spin transport within devices. Notably, chiral systems often outperform non-chiral ones in terms of conversion efficiency and facilitate long-range spin transport, which makes them relevant for both fundamental and applied physics. After examining the archetypal example of the chiral crystal, elemental tellurium, and the studies of spin selectivity in Weyl semimetals, we discuss its origin in terms of the unconventional (collinear) Rashba–Edelstein effect. We also explore key factors affecting the conversion efficiency and robustness of spin transport, focusing on persistent spin textures and their influence on spin lifetime. In addition, we discuss the potential impact of band velocities and the role of orbital contributions, as well as the differences associated with reduced dimensionality, providing a roadmap for guiding future theoretical, experimental, and applied studies. [ABSTRACT FROM AUTHOR]

Antiferromagnets exhibit ultrafast magnetization precession, which has the potential to enable the development of terahertz spin torque nano-oscillators. By utilizing perpendicularly magnetized magnetic nanopillars with a synthetic antiferromagnetic (SAF) free layer, we have demonstrated through theoretical and numerical analysis that stable out-of-plane precession states can be achieved by applying current and an electric field. In the case of small current, the two magnetic layers of the SAF are in antiparallel alignment and rotate around the z-axis with the precession frequency decreasing as the current strength increases. When the current-induced spin torque is strong enough to fully overcome the antiferromagnetic coupling, the SAF free layer is driven into a scissor-like precession state around the z-axis with the frequency increasing with current. By selecting the appropriate combination of the current and electric field, the magnetization precession orbits and precession frequencies can be adjusted. These controllable procession orbits with tunable frequencies and fixed magnetization precession amplitude may be a promising candidate for implementing binary frequency shift keying modulation techniques. [ABSTRACT FROM AUTHOR]

The organic electron flashing ratchet experiment describes the phenomenon in which an electric current can be detected, even in the absence of a net potential bias. To understand the experimental mechanism at the quantum level, we utilize the quantum nonadiabatic method to simulate the electron dynamics in an organic polymer chain with the flashing ratchet potential. It is found that electrons exhibit directional migration with a velocity, which depends on both the asymmetry and the flashing frequency of the ratchet potential. In addition, the flashing ratchet, which describes the non-uniform and time-varying electric field, increases the velocity by 58.6% compared to the uniform electric field. The flashing ratchet effect exists intrinsically in actual organic photovoltaics (OPVs), due to the naturally uneven and time-varying inherent electric field caused by various inevitable factors in bulk heterojunctions (BHJ). Moreover, the ratchet potential can be artificially constructed by designing the morphology of the BHJ, which opens a promising avenue for driving electrons to accelerate directional migration, and improving the photoelectric conversion efficiency of OPVs. [ABSTRACT FROM AUTHOR]

We report the fabrication and testing, at 4.2 K, of an S1IS2FS3 device, where S, F, and I denote a superconductor (Nb), a ferromagnetic material (Permalloy), and an insulator (AlOx), respectively. The F layer covers about one half of the top electrode of the S1IS2 Josephson junction and is positioned off-center. Electric current, Itr, along the S3 electrode can change the magnetization of the F layer in such a way that, for one direction of Itr, a magnetic flux penetrates the junction perpendicular to the layers, whereas for the opposite direction, the perpendicular magnetic flux can be removed. In the former state, the modulation pattern of the Josephson critical current, Ic, in the magnetic field, H, may acquire minimum near H = 0 and restores its usual shape with maximum in the second state. These states can be used for building a compact cryogenic memory compatible with single flux quantum electronics. [ABSTRACT FROM AUTHOR]

4f electron-based topological Kondo insulators have long been researched for their potential to conduct electric current via protected surface states, while simultaneously exhibiting unusually robust insulating behavior in their interiors. To this end, we have investigated the electrical transport of the 3d-based correlated insulators FeSi and FeSb2, which have exhibited enough similarities to their f electron cousins to warrant investigation. By using a double-sided Corbino disk transport geometry, we show unambiguous evidence of surface conductance in both of these Fe-based materials. In addition, by using a four-terminal Corbino inverted resistance technique, we extract the bulk resistivity as a function of temperature. Similar to topological Kondo insulator SmB6, the bulk resistivity of FeSi and FeSb2 is confirmed to exponentially increase by up to 9 orders of magnitude from room temperature to the lowest accessible temperature. This demonstrates that these materials are excellent bulk insulators, providing an ideal platform for studying correlated 2D physics. [ABSTRACT FROM AUTHOR]

4f electron-based topological Kondo insulators have long been researched for their potential to conduct electric current via protected surface states, while simultaneously exhibiting unusually robust insulating behavior in their interiors. To this end, we have investigated the electrical transport of the 3d-based correlated insulators FeSi and FeSb2, which have exhibited enough similarities to their f electron cousins to warrant investigation. By using a double-sided Corbino disk transport geometry, we show unambiguous evidence of surface conductance in both of these Fe-based materials. In addition, by using a four-terminal Corbino inverted resistance technique, we extract the bulk resistivity as a function of temperature. Similar to topological Kondo insulator SmB6, the bulk resistivity of FeSi and FeSb2 is confirmed to exponentially increase by up to 9 orders of magnitude from room temperature to the lowest accessible temperature. This demonstrates that these materials are excellent bulk insulators, providing an ideal platform for studying correlated 2D physics. [ABSTRACT FROM AUTHOR]

Test masses of future laser interferometric gravitational-wave detectors will be made of high-purity silicon and cooled, in particular, to 123 K in the LIGO Voyager project. Electrostatic actuators are supposed to be used to tune the test mass position. Capacitive coupling of the actuator electrodes with the silicon test mass results in the mechanical loss caused by electric currents flowing in silicon having a finite resistivity. This loss is a cause of additional thermal noise. In this study, we present the results of temperature dependence of the electric field induced loss in the bending vibration mode of commercial disk-shaped undoped silicon wafers in the temperature range of 100–295 K. [ABSTRACT FROM AUTHOR]

We present an experimental technique to generate and measure a temperature bias in the quantum Hall effect of GaAs/AlGaAs Corbino samples. The bias is generated by injecting an electric current at a central resistive heater, and the resulting radial temperature drop is determined by conductance measurements at internal and external concentric rings. The experimental results agree with the predictions of numerical simulations of the heat flow through the substrate. We also compare these results with previous predictions based on the thermoelectric response of these devices. [ABSTRACT FROM AUTHOR]

In this work, we test the thermal rupture of a permalloy strip when an electric current is flowing through the strip. For a strip with the top surface exposed to air or covered with a thin insulating layer, we find that the strip gets destroyed at a DC density of only ∼0.6 × 1012 A/m2 and a temperature smaller than 400 K, while it can withstand ∼1.5 × 1012 A/m2 and ∼1200 K if the current is delivered in a sub-μs pulse. If the permalloy strip is covered with a heat dissipation window of Ta2O3/Pt or Ta2O3/Au, so the permalloy can also conduct heat through the top surface, the strip can withstand ∼3.5 × 1012 A/m2 and ∼2000 K. Interestingly, the strips always break in a section not covered by the dissipation window, even if that is not the hottest part of the strip. Therefore, the layers forming the dissipation window help with not only extracting the heat but also delaying the structural damage. [ABSTRACT FROM AUTHOR]

Magnetic skyrmions are currently gaining attention owing to their potential to act as information carriers in spintronic devices. However, conventional techniques which rely on modulating the electric current to write or manipulate information using skyrmions are not energy efficient. Therefore, in this study, a Ta/Co–Fe–B/Ta/MgO junction that hosts a skyrmion was utilized to fabricate a device to investigate the effect of applying a voltage in the direction perpendicular to the film plane. Magneto-optical Kerr effect microscopy was performed in a polar configuration to observe the difference in the perpendicular magnetic anisotropy by observing the behavior of the magnetic domain structure and the skyrmions. Our findings suggest that voltage-induced magnetic domain structure modulation and the creation/annihilation of skyrmions are both possible. Furthermore, manipulation of skyrmions was realized by utilizing repulsive magnetic dipole interaction between the voltage-created skyrmion and skyrmion, exhibiting Brownian motion, outside the top electrode. Thus, our proposed method can enable controlling the creation and annihilation of skyrmions and their positions by manipulating the externally applied voltage. These findings can advance unconventional computing fields, such as stochastic and ultra-low-power computing. [ABSTRACT FROM AUTHOR]

The switching of perpendicularly magnetized ferromagnets via current-induced spin–orbit torques is of great interest because of its potential applications in memory and logic devices. However, the in-plane electric current itself is not enough to switch the magnetization. In addition to the electric current, an in-plane external magnetic field is required for magnetization switching. This limits the usage of such devices in spintronic applications. Here, we work on the current-driven perpendicular magnetization switching in the Pt/Ta(wedge)/CoFeB/MgO multilayer. The structural symmetry is broken in both z-axis and in-plane due to the wedge Ta layer, which results in a field-like spin–orbit torque. The β z value extracted from the slope of the offset field vs current density increases with Ta layer thickness (<1.0 nm) and then decreases up to <1.3 nm. Thanks to both in-plane and z-axis asymmetries that enable the current-driven magnetization switching without the need for a magnetic field. We showed switching of the magnetization with a perpendicular magnetic anisotropy, switching in a wide range of Ta layer in Pt/Ta(wedge)/CoFeB/MgO multilayer. [ABSTRACT FROM AUTHOR]

Perpendicular magnetization switching driven by spin–orbit torques plays an increasingly important role for spintronic devices toward practical applications but is also hindered by the well-known technical challenge that an external in-plane magnetic field is required for deterministic switching. Here, we show that the deterministic switching can be achieved in synthetic antiferromagnets through the flexible domain control in the absence of external magnetic fields. Specifically, we have observed that the domain wall (DW) distorts under an applied electric current in contrast to the conventional rigid DW motion in a single ferromagnet. More importantly, the distorted DWs can be precisely controlled under zero magnetic field, leading to the deterministic switching. Our results indicate that the critical technical challenge may be addressed by employing a synthetic antiferromagnetic layer through the DW motion dominated field-free switching. [ABSTRACT FROM AUTHOR]

We theoretically propose a mechanism of thermoelectric power generation via transverse thermo-spin conversions. We consider a material with strong spin–orbit coupling (the target material) and apply a temperature gradient to the target material, where the temperature gradient induces a transverse spin current. By attaching ferromagnets to the target material, we show the conversion of the nonequilibrium spin accumulation induced by the spin current into the electric voltage based on an extension of the Valet–Fert theory used in the giant magnetoresistive effect. A series circuit application is also discussed. [ABSTRACT FROM AUTHOR]

For real-world applications, it is desirable to realize field-free spin–orbit torque (SOT) switching in thin films with high perpendicular magnetic anisotropy (PMA). In this paper, we report that field-free SOT switching in a L10-FePt single layer with a large switching ratio of 26% is obtained by using a MgO ⟨100⟩⋀8°/⟨100⟩ miscut substrate. It is found that field-free switching depends on the direction of the imposed pulse current. Only when the electric current is along the y (010)-direction but not along the x (100)-direction does field-free switching happen, which can be attributed to the tilted PMA induced symmetry breaking in the x–z plane. Furthermore, under the field-free condition, our FePt single layer system exhibits stable multi-state magnetic switching behavior and nonlinear synaptic characteristics. This work paves the way to realize field-free SOT switching in the L10-FePt single layer, which will have significant impact on spin memory devices and synaptic electronics. [ABSTRACT FROM AUTHOR]

A concept of optically triggered and electrically controlled ultra-fast neuromorphic computing processor based on an antiferromagnetic/heavy metal (AFM/HM) heterostructure is proposed. The AFM/HM-based artificial neurons are excited with short THz-range pulses, triggering precession in AFM. Bias electric current in the HM layer can be used to modify the resonance frequency of precession. The conversion of the precession into the electric current in the HM-layer occurs via the inverse spin Hall effect. A model of a neuromorphic processor is, thus, proposed, consisting of excitatory AFM-based artificial neurons—oscillators, and processing neurons—detectors. We show that the use of optical excitation can significantly increase the processing speed of neuromorphic computing at low power consumption. Examples of the implementation of the simplest logical operations (OR, AND) are demonstrated. [ABSTRACT FROM AUTHOR]

The conversion efficiency η of a thermoelectric (TE) device can be effectively improved by constructing segmented TE legs, but the specific interfaces between the heterogeneous materials inevitably degrade the performance. Focusing on the Bi2Te3-based two-segmented module, we systematically investigated the influences of the Peltier effect, interfacial electrical resistance Re, and interfacial thermal resistance Rt on the conversion efficiency η. It is found that the Peltier heat can increase the conversion efficiency if the Seebeck coefficient increases along the direction of an electric current. An applicable Re should be kept on the order of magnitudes of 10−5 Ω cm2 for segmented TE devices, since the increased Re significantly decreases η. With a determined Re, η depends on the leg height L rather than the cross-sectional area A. In contrast, η is hardly affected by the variation in the interfacial thermal resistance Rt, while both the input heat flux Qin and output power P decrease with the increasing Rt. [ABSTRACT FROM AUTHOR]

The direct control of the tunneling current as a function of electric polarization in ferroelectric tunnel junctions has recently attracted noticeable attention through the availability of the CMOS compatible ferroelectric hafnium zirconium oxide (H f 0.5 Z r 0.5 O 2 ). While a lot of progress has been made in the understanding of ferroelectric tunnel junctions, the control and optimization of the volume fraction of the polar orthorhombic phase are still in its infancy and raise the question whether all observed resistive switching events are necessarily associated with polarization reversal. Trap-assisted tunneling is also able to modulate the current density through a field-induced variation of the oxygen vacancy density across the tunnel junction. The amplitude of the effect should depend on the pre-existing density of oxygen vacancies introduced during the fabrication. Here, by controlling the oxygen partial pressure during the RF magnetron sputtering deposition of the non-polar monoclinic phase of H f 0.5 Z r 0.5 O 2 thin films of approximately 3 nm, we demonstrate tuning of its transport mechanism due to the formation of oxygen vacancies. We show that two mechanisms dominate the current transport depending on the average distance between traps. For large oxygen content in the H f 0.5 Z r 0.5 O 2 thin film, direct tunneling (DT) is the dominant transport mechanism, while the electrical conductivity in the oxide can be described by the phonon-assisted tunneling between traps (PATTs) for the oxygen deficient H f 0.5 Z r 0.5 O 2 thin film. We derive a critical inter-trap distance and a critical thickness value that explains the transition from DT to PATT mechanism in H f 0.5 Z r 0.5 O 2 thin films. [ABSTRACT FROM AUTHOR]

Antiferromagnets are promising materials for future spintronic applications due to their unique properties including zero stray fields, robustness vs external magnetic fields, and ultrafast dynamics, which have attracted extensive interest in recent years. In this work, we investigate the dynamics of isolated skyrmions in an antiferromagnetic nanotrack with a voltage-gated region. It is found that the skyrmion can be jointly controlled by the driving current and the voltage-controlled magnetic anisotropy gradient. We further propose a design of logic computing gates based on the manipulation of antiferromagnetic skyrmions, which is numerically realized combining several interactions and phenomena, including the spin Hall effect, voltage-controlled magnetic anisotropy effect, skyrmion–skyrmion interaction, and skyrmion–edge interaction. The proposed logic gates can perform the basic Boolean operations of the logic AND, OR, NOT, NAND, and NOR gates. Our results may have a great impact on fundamental physics and be useful for designing future nonvolatile logic computing devices with ultra-low energy consumption and ultra-high storage density. [ABSTRACT FROM AUTHOR]

Synthetic antiferromagnetic spintronics is an important field of study in the area of spintronics. Here, we fabricate a wedged-Ru layer in a ferromagnet/Ru/ferromagnet stack with alternating antiferromagnetic and ferromagnetic exchange-couplings. We systematically investigate the effect of the interlayer exchange coupling J on the chiral domain wall dynamics. The domain wall moves along the wedge unidirectionally driven by an out-of-plane magnetic field in the antiferromagnetically exchange-coupled region. In the ferromagnetically exchange-coupled region, only field-induced maze domain walls can be observed. The boundary between the antiferromagnetically and ferromagnetically exchange-coupled regions can be identified according to the behavior of domain walls. The strongest antiferromagnetic exchange coupling point Jmax in our sample is determined. A simple phenomenological picture is proposed to explain our experimental results. Moreover, we demonstrate that the Néel-type domain wall near the boundary of J = 0 could be driven into motion by an applied electric current. A stripe domain wall can be observed at the boundary of J = 0 only with a negative electric current resulting from the domain wall chirality. Our results may provide a platform to investigate the domain wall chirality and pave a way to spintronic devices based on synthetic antiferromagnets. [ABSTRACT FROM AUTHOR]

We report on the depinning of nearly commensurate charge-density waves in 1T-TaS2 thin films at room temperature. A combination of the differential current–voltage measurements with the low-frequency noise spectroscopy provides unambiguous means for detecting the depinning threshold field in quasi-2D materials. The depinning process in 1T-TaS2 is not accompanied by an observable abrupt increase in electric current—in striking contrast to depinning in the conventional charge-density-wave materials with quasi-1D crystal structure. We explained it by the fact that the current density from the charge-density waves in the 1T-TaS2 devices is orders of magnitude smaller than the current density of the free carriers available in the discommensuration network surrounding the commensurate charge-density wave islands. The depinning fields in 1T-TaS2 thin-film devices are several orders of magnitude larger than those in quasi-1D van der Waals materials. Obtained results are important for the proposed applications of the charge-density wave devices in electronics. [ABSTRACT FROM AUTHOR]

The interplay between curvature and magnetization is a cornerstone in magnetism. Thus, in this work, we address the role of curvature on the propagation of magnetic skyrmions along a curved race track. Using a micromagnetic approach and simulations, we observed the creation of a curvature-induced force (CIF) that acts on the skyrmion while traveling along the track. We also show that curvature can stop the skyrmion if the current density is below a critical value. Above this limit, the skyrmion goes through the defect, a direct consequence of the CIF. Our results allow a better definition of the electric current needed for moving skyrmions along curved tracks. [ABSTRACT FROM AUTHOR]

We propose a time-delay oscillator using Mackey–Glass nonlinearity based on a pinned magnetic domain wall in a thin film nanostrip. Through spin transfer torques, electric currents applied along the strip cause the domain wall to deform and displace away from a geometrical pinning site, which can be converted into a nonlinear transfer function through a suitable choice of a readout. This readout serves as a delay signal, which is subsequently fed back into the applied current with amplification. With micromagnetics simulations, we study the role of the readout position, time delay, and feedback gain on the dynamics of this domain wall. In particular, we highlight regimes in which self-sustained oscillations and complex transients are possible. [ABSTRACT FROM AUTHOR]

Traveling spin waves in magnonic waveguides undergo severe attenuation, which tends to result in a finite propagation length of spin waves, even in magnetic materials with the accessible lowest damping constant, heavily restricting the development of magnonic devices. Compared with the spin waves in traditional waveguides, propagating spin waves along the strip domain wall are expected to exhibit enhanced transmission. Here, we demonstrate theoretically and through micromagnetic simulations that spin–orbit torque associated with a ferromagnet/heavy metal bilayer can efficiently control the attenuation of spin waves along a Néel-type strip domain wall despite the complexity in the ground-state magnetization configuration. The direction of the electric current applied to the heavy-metal layer determines whether these spin waves are amplified or further attenuated otherwise. Remarkably, our simulations reveal that the effective current densities required to efficiently tune the decay of such spin waves are just ∼1010 A m−2, roughly an order smaller than those required in conventional spin waveguides. Our results will enrich the toolset for magnonic technologies. [ABSTRACT FROM AUTHOR]

Energy conservation and battery life extension are key challenges for the next-generation hybrid electric vehicles. In particular, the temperature and electric currents in a storage battery need to be monitored simultaneously with ∼1 kHz signal bandwidth for optimum battery usage. Here we introduce a centimeter-scale portable quantum sensor head, consisting of a diamond substrate hosting an ensemble of nitrogen-vacancy (NV) color centers with a density of ∼3 × 1017 cm−3. One diamond surface is attached to a multi-mode fiber for simultaneous optical excitation and readout of the NV centers, while the other diamond surface is attached to a coplanar microwave guide for NV spin ground-state mixing. Signal bandwidth of 1 kHz was realized through time-domain multiplexing of the two-tone microwave frequency modulation at 20 kHz. Two microwave frequencies were locked to the two resonance points that were determined from the optically detected magnetic resonance spectrum. From the mean and the difference of the deviation from the two locked frequencies, the temperature and magnetic field were obtained simultaneously and independently, with sensitivities of 3.5 nT/Hz1/2 and 1.3 mK/Hz1/2, respectively. We also showed that our sensor reached a minimum detectable magnetic field of 5 pT by accumulating signals for over 10 000 s. [ABSTRACT FROM AUTHOR]

In this paper, we argue that the electron skew scattering on paramagnetic impurities in non-magnetic systems, such as bulk semiconductors, possesses a remarkable fingerprint, allowing us to differentiate it directly from other microscopic mechanisms of the emergent Hall response. We demonstrate theoretically that the exchange interaction between the impurity magnetic moment and mobile electrons leads to the emergence of an electric Hall current persisting even at zero electron spin polarization. We describe two microscopic mechanisms behind this effect, namely, the exchange interaction-assisted skew scattering and the conversion of the spin Hall effect-induced transverse spin current to the charge one owing to the difference between the spin-up and spin-down conductivities. We propose an essentially all-electric scheme based on a spin-injection ferromagnetic-semiconductor device, which allows one to reveal the effect of paramagnetic impurities on the Hall phenomena via the detection of the spin polarization-independent terms in the Hall voltage. [ABSTRACT FROM AUTHOR]

A magnetic toron is a spatially localized three-dimensional spin texture composed of skyrmionic layers with two Bloch points at its two ends. The magnetic toron can, thus, be stabilized in chiral magnets using external fields. In this work, we studied the toron dynamics induced by electric currents in a cylindrical nanowire using micromagnetic simulations. We show that the toron performs a unidirectional motion in a nanowire where the current is applied along the wire direction. The current-induced toron motion can be divided into three regions: static region for a small current due to the pinning effect, toron moving region for a large current, and toron annihilation region for a large reversal current. Moreover, the moving direction can be tuned by the sign of Dzyaloshinskii–Moriya interaction. Such peculiar dynamics indicates that the magnetic toron is a possible candidate as an information carrier. [ABSTRACT FROM AUTHOR]

We analytically calculate the anomalous transverse electric and thermal currents in massive and tilted Dirac systems, using β-borophene as a representative material, and report on conditions under which the corresponding Lorenz number (L a n ) deviates from its classically accepted value (L 0) . The deviations in the high-temperature regime are shown to be an outcome of the quantitative difference in the respective kinetic transport expressions for electric (σ) and thermal (κ) conductivity and are further weighted through a convolution integral with a non-linearly energy-dependent Berry curvature that naturally arises in a Dirac material. In addition, the tilt and anisotropy of the Dirac system that are amenable to change via an external stimulus are found to quantitatively influence L a n . The reported deviations from L 0 hold practical utility inasmuch as they allow an independent tuning of σ and κ, useful in optimizing the output of thermoelectric devices. [ABSTRACT FROM AUTHOR]

The strong electric current in spark plasma sintering (SPS) often gives sintered materials unique microstructures. In the present study, it is found that the Co3W grains formed at the W/Co bonding interface preferentially grow along [2 1 ¯ 1 ¯ 0] (or its equivalent orientations) in the current direction during SPS, which is significantly different from that without current. We propose that the resistance anisotropy of grains under electromigration leads to anisotropic atomic diffusion, inducing the preferential growth of grains under current. This work may provide an approach and a theoretical foundation for the preparation of materials exhibiting directional growth. [ABSTRACT FROM AUTHOR]

Electrical properties of Al2O3/hydrogenated-diamond (H-diamond) metal-oxide-semiconductor (MOS) capacitors are investigated and discussed in this study. Al2O3 gate dielectrics are deposited at 120, 200, and 300 °C by an atomic layer deposition technique. For the H-diamond MOS capacitors with Al2O3 deposited at 120, 200, and 300 °C, leakage current densities at an electric field of 3.0 MV cm−1 are 8.4 × 10−4, 7.1 × 10−6, and 7.5 × 10−5 A cm−2, respectively. A small decrease in the maximum capacitance of the Al2O3 (120 °C)/H-diamond MOS capacitor is observed when the measurement frequency is increased from 1 kHz to 100 kHz. However, the maximum capacitances of the Al2O3 (200 °C)/H-diamond and Al2O3 (300 °C)/H-diamond MOS capacitors are stable. Experimental flatband voltage in the capacitance–voltage curve of the Al2O3 (120 °C)/H-diamond MOS capacitor shifts to the left with respect to theoretical flatband voltage. However, they shift to the right for the Al2O3 (200 °C)/H-diamond and Al2O3 (300 °C)/H-diamond MOS capacitors. Therefore, when the deposition temperature of Al2O3 is increased from 120 to 300 °C, polarity of the fixed charges in the H-diamond MOS capacitors changes from positive to negative. This phenomenon is explained by the variations of negatively charged acceptors at the Al2O3/H-diamond interface and oxygen vacancies in the Al2O3 film. [ABSTRACT FROM AUTHOR]

Spin orbit torque-driven magnetization switching in perpendicularly magnetized thin film relies on an extra in-plane magnetic field to break the in-plane magnetic symmetry, which is an obstacle for the integration of spin–orbit torque-based spintronic devices. Here, we propose a simple method to realize the field-free spin–orbit torque-driven magnetization switching by exploiting a tilted magnetic anisotropy, which is caused by the direct coupling of two ferromagnetic layers in the Pt/Co/FeNi/Ta structure. When preparing the sample, a 1000 Oe in-plane magnetic field was applied to ensure the magnetic moment deviating a small angle from the out-of-plane direction to this in-plane field direction. We experimentally demonstrate the deterministic field-free magnetization switching in Pt/Co/FeNi/Ta by the field-like spin–orbit torques when the electric current is applied perpendicular to this in-plane field direction. The switching performance is slightly degraded with the critical switching current density and thermal stability factor, respectively, reaching 6.4 × 106 A/cm2 and 25 due to the slightly decreased spin–orbit torque efficiency and perpendicular magnetic anisotropy with introducing the FeNi layers. Our work paves the way for realizing the field-free magnetization switching by spin–orbit torques. [ABSTRACT FROM AUTHOR]

Lyotropic chromonic liquid crystals (LCLCs) combine a very high packing density (intramolecular separation is about 3.4 Å within aggregates) with an ability to form ordered structures that are transferable from a water solution to a dry film. We show that the electric current in a dry film of LCLC aggregates is sensitive to the distance between the molecules in the aggregates and that it depends on the ambient humidity. Thus, by measuring the electric current through an LCLC film printed onto a substrate with predesigned electrodes and integrated circuits, we can measure the humidity. A humidity sensor based on LCLCs has high sensitivity, a fast response, and short recovery times. [ABSTRACT FROM AUTHOR]

Current-induced magnetization has been investigated in a monoaxial chiral crystal CrNb3S6 by means of superconducting quantum interference device magnetometry. We found that bulk magnetization was generated by applying electric current along the principal axis of the monoaxial chiral crystal and that the magnetization changed linearly with the current. Directly detecting such magnetization enables one to estimate the number of spin-polarized electrons. Using this number, we evaluated the spin polarization rate within the framework of Boltzmann's equation. We also observed that the current-induced magnetization increased in the vicinity of the phase boundary between paramagnetic and forced ferromagnetic phases, which could be attributed to the enhancement of spin fluctuation. We discuss these observations based on a chirality-induced spin selectivity effect enhanced by exchange interactions. [ABSTRACT FROM AUTHOR]

We report on a theoretical study of thermal magnetization switching induced by nanosecond electric current pulse using Lagrangian formalism based on the Landau–Lifshitz–Gilbert equation. The parameters for modeling are obtained from the measurements of the anomalous Hall resistance at different probe currents. We obtain the switching diagrams, analyze how the switching rate depends on the pulse parameters and the applied magnetic field, and find the optimal set of values such as orientation of the field, electric pulse duration, and energy consumption. We find that the magnetization switching is particularly efficient near the compensation point, where a decrease in the magnetization of the rare-earth sublattices by 10% or less can lead to reversal of net magnetization. [ABSTRACT FROM AUTHOR]

In the search of material properties out-of-equilibrium, the non-equilibrium steady states induced by electric current are an appealing research direction where unconventional states may emerge. However, the unavoidable Joule heating caused by flowing current calls for the development of new measurement protocols, with particular attention to the physical properties of the background materials involved. Here, we demonstrate that localized heating can give rise to a large, spurious diamagnetic-like signal. This occurs due to the local reduction of the background magnetization caused by the heated sample, provided that the background material has a Curie-like susceptibility. Our experimental results, along with numerical calculations, constitute an important building block for performing accurate magnetic measurements under the flow of electric current. [ABSTRACT FROM AUTHOR]

Magnetic insulators (MIs) have attracted great attention because of their low Gilbert damping, long spin transmission length, and no Ohmic loss. In this study, the high quality TbIG films with perpendicular magnetic anisotropy were epitaxially grown on GGG (111) substrates. In TbIG/Pt bilayers, the angular dependence of coercivity is found to obey the Kondorsky model, suggesting the magnetization reversal mechanism of magnetic domain nucleation and expansion. The transverse component of spin Hall magnetoresistance (SMR), which is analogous to the planar Hall resistance in a ferromagnetic metal, is found to be about seven times larger than the SMR-induced anomalous Hall resistance (analogous to the anomalous Hall resistance in a ferromagnetic metal). Moreover, the phase diagrams of the current-induced magnetization switching with different angles and magnitudes of the assisting magnetic field were drawn for the TbIG/Pt bilayers. The current-induced damping-like effective field (HDL) characterized by the harmonic measurements was evaluated to be about 164 Oe/ 10 8 A cm − 2 . By providing a comprehensive investigation of magnetization switching behaviors in MIs, our results will promote the application of ultralow-dissipation MI based spintronic devices. [ABSTRACT FROM AUTHOR]

Interfaces between two topological insulators are of fundamental interest in condensed matter physics. Inspired by experimental efforts, we study interfacial processes between two slabs of BiSbTeSe 2 (BSTS) via first principles calculations. Topological surface states are absent for the BSTS interface in its equilibrium separation, but our calculations show that they appear if the inter-slab distance is greater than 6 Å. More importantly, we find that topological interface states can be preserved by inserting two or more layers of hexagonal boron nitride between the two BSTS slabs. In experiments, the electric current tunneling through the interface is insensitive to back gate voltage when the bias voltage is small. Using a first-principles based method that allows us to simulate the gate field, we show that at low bias, the extra charge induced by a gate voltage resides on the surface that is closest to the gate electrode, leaving the interface almost undoped. This provides clues to understand the origin of the observed insensitivity of transport properties to back voltage at low bias. Our study resolves a few questions raised in experiment, which does not yet offer a clear correlation between microscopic physics and transport data. We provide a road map for the design of vertical tunneling junctions involving the interface between two topological insulators. [ABSTRACT FROM AUTHOR]

A gate voltage application in a Si-based spin metal-oxide-semiconductor field-effect transistor (spin MOSFET) modulates spin accumulation voltages, where both electrical conductivity and drift velocity are modified while keeping constant electric current. An unprecedented reduction in the spin accumulation voltages in a Si spin MOSFET under negative gate voltage applications is observed in a high electric bias current regime. To support our claim, the electric bias current dependence of the spin accumulation voltage under the gate voltage applications is investigated in detail and compared with a spin drift diffusion model including the conductance mismatch effect. The drastic decrease in the mobility and spin lifetime in the Si channel is ascribable to the optical phonon emission at the high electric bias current, which consequently reduced the spin accumulation voltage. [ABSTRACT FROM AUTHOR]

A photoelectric cantilever-based current sensing methodology, mainly composed of a cantilever, a magnet, an analyzer, and a photodiode, for passive measuring diverse multiline cables with diverse currents, is proposed for the desirable application of a Wireless Sensor Node (WSN) in Internet of Things (IoT). The basic idea is to achieve a synchronous vibration of both the analyzer and the cantilever to modulate the natural light signal incident on the photodiode. In this Letter, the magnet, fixed at the end of the cantilever, is used to passively convert the applied current induced magnetic force into a cantilever vibration, which is further converted to a polarization angle variation via the above synchronous vibration. The natural light signal is accordingly modulated and a varied voltage, as a function of the applied current, is thus output from the photodiode. A two-wire DC electric current is used to verify the validity of the sensing mechanism. The measurement error can be decreased to less than half of the theoretical one by calibration, and the linear range can be further adjusted by changing a value on the host computer. Compared to the piezoelectric cantilever-based one, the proposed photoelectric cantilever-based methodology can achieve a continuous measurement of DC and its variation with a higher resolution, and both a faster response and a higher resolution for AC, and thus is more suitable for IoT applications. [ABSTRACT FROM AUTHOR]

We report on a simple yet efficient approach allowing direct electrothermal excitation of parametric resonance (PR) in double-clamped flexible nano- and microscale beams. The application of a time-harmonic voltage between the beam's ends leads to the electric current and Joule's heating of the entire beam, which induces a time-periodic axial stress and results in excitation of the structure lateral vibrations through the PR mechanism. The proposed approach has an advantage, simplifying fabrication and integration and reducing the influence of residual stress, and thermal mismatch, unlike conventional piezoelectric, photothermal, or electrostatic actuation approaches, which require additional piezoelectric layers, light sources, or electrodes in the proximity of a vibrating beam. Single crystal silicon, nominally 500 μm long, 30 μm wide, and 5 μm thick beams were fabricated by deep reactive ion etching and operated at a pressure of ≈ 1.9 mTorr. The experimental results, consistent with the reduced order and numerical model predictions, demonstrate the feasibility of the suggested excitation scenario, which could be implemented in resonant sensors, timing devices, signal processing, and micro and nanomechanical logical elements. [ABSTRACT FROM AUTHOR]

The double magnetic proximity effect (MPE) in an Fe/Fe0.30V0.70 superlattice is studied by a direct measurement of the magnetization profile using polarized neutron reflectivity. The experimental magnetization profile is shown to qualitatively agree with a profile calculated using density functional theory. The profile is divided into a short range interfacial part and a long range tail. The interfacial part is explained by charge transfer and induced magnetization, while the tail is attributed to the inhomogeneous nature of the FeV alloy. The long range tail in the magnetization persists up to 170% above the intrinsic ordering temperature of the FeV alloy. The observed effects can be used to design systems with a direct exchange coupling between layers over long distances through a network of connected atoms. When combined with the recent advances in tuning and switching, the MPE with electric fields and currents, the results can be applied in spintronic devices. [ABSTRACT FROM AUTHOR]

In addition to electric fields and currents, light can also provide an approach to modulate the ferromagnetism with low energy consumption. BiFeO3, with features of relatively small bandgap and large polarization, provides an opportunity for investigating the optical modulation of magnetism. In this work, pure-phase BiFeO3 nanocrystals embedded in Al2O3 films are synthesized. It is demonstrated that the strain generated and accumulated during the growth process of BiFeO3 nanocrystals can lead to the modification of the atomic structure and thus produce a strain engineered bandgap. A distinguished light-modulated ferromagnetism is observed in BiFeO3 nanocrystals. Contributed by the strain engineered bandgap, the ferromagnetism of BiFeO3 nanocrystals can be modulated and enhanced more efficiently by light irradiation. It paves the way for modulating the ferromagnetic properties of BiFeO3 nanocrystals via bandgap engineering, which has promising applications in modern information technology. [ABSTRACT FROM AUTHOR]

An accurate standard of electric current is a long-standing challenge of modern metrology. It has been predicted that a superconducting nanowire in the regime of quantum fluctuations can be considered as the dynamic equivalent of a chain of conventional Josephson junctions. In full analogy with the quantum standard of electric voltage based on the Josephson effect, the quantum phase slip phenomenon in ultrathin superconducting nanowires could be used for building the quantum standard of electric current. This work presents advances toward this ultimate goal. [ABSTRACT FROM AUTHOR]

Electronic structures and topological properties of silicene adsorbed with 5d transition metal atom Ta (silicene-Ta) are investigated by using the first-principles calculations. The Ta atom prefers to adsorb at the hollow site of silicene. We demonstrate that the quantum anomalous Hall (QAH) effect can be realized in the studied silicene-Ta system, whose Fermi level is found to be located exactly inside the spin-orbit coupling induced nontrivial bulk band gap. In addition, the heterostructure of silicene-Ta/BN is built and explored. By applying an external vertical electric field, the realized topologically nontrivial bulk band gap can be enlarged effectively. Our calculations show that the achieved QAH effect is robust against the Ta adatom adsorption coverage (∼1%–6%) and disorder, making the experimental observation highly flexible. Our findings will greatly promote the experimental realization and practical application of the QAH effect in silicene-based systems. [ABSTRACT FROM AUTHOR]