Strong Torque Research Articles

Strong Spin-Orbit Torque Induced by the Intrinsic Spin Hall Effect in Cr1−xPtx

We report on a spin-orbit torque study of the spin current generation in Cr1-xPtx alloy, using the light 3d ferromagnetic Co as the spin current detector. We find that the dampinglike spin-orbit torque of Cr1-xPtx/Co bilayers can be enhanced by tuning the Cr concentration in the Cr1-xPtx layer, with a maximal value of 0.31 at the optimal composition of Cr0.2Pt0.8. We find that the spin current generation in the Cr1-xPtx alloy can be fully understood by the characteristic trade-off between the intrinsic spin Hall conductivity of Pt and the carrier lifetime in the dirty limit. We find no evidence for the spin current generation by other mechanisms in this material, revealing that the role of Cr is found to be simply the same as other metals and oxides in previous studies. This work also establishes the low-resistivity Cr0.2Pt0.8 as an energy-efficient spin-orbit torque provider for magnetic memory and computing technologies.

Wind Turbines Control Trends and Challenges: An Overview

Wind turbines (WTs) create electricity by utilizing the energy of the wind. As a result, wind turbine control and cost-effective operation were studied. The control system offers a long service life, maximum energy output, and safety. On control methods and control strategies, various ways for limiting and optimizing energy consumption were discussed. Integration of wind power may compromise the stability of the transient system. Asynchronous induction generators cannot handle the quantity of reactive power generated in wind energy applications. WTs are usually constructed to withstand inclement weather but not for high speeds or torque. Strong aerodynamic torques or rotational speeds are capable of destroying WT blades. To prevent this, WTs always have a cutout speed over which the turbine will be stopped by its brakes. When excessive wind speeds endanger the safety of the turbines, the WT employs a range of control techniques. As a result, all WTs are constructed using a power control method. This can regulate pitch and stall. Passive or active stall control can be applied to the WT. Therefore, this study analyzed the associated technologies, the maintenance of wind turbines, the cost, the many types of wind turbine controllers, and the negative effects and roadblocks unique to the wind energy industry.

The giant orbital Hall effect in Cr/Au/Co/Ti multilayers

The spin–orbit torques originating from the spin Hall effect of heavy metals are of vital importance for applications in spintronics due to its low consumption of energy. Theoretical calculations have predicted that 3d and 4d light metals can produce a similar amount of torques to heavy metals via the strong orbital Hall effect (OHE). However, few experiments have been conducted since it is technically challenging to directly detect the orbital current from the OHE. Here, we report an effective approach to demonstrate the strong orbital torques in the light metal Cr with the aid of a conversion process from the orbital current to the spin current by introducing an Au interfacial layer in the Cr/ferromagnet structures. A rather large orbital torque efficiency and an increase with the increasing thickness of the Cr-layer are attained in the perpendicularly magnetized Cr/Au/Co/Ti multilayers. Moreover, an energy efficient magnetization switching and the domain wall motion in Cr/Au/Co/Ti multilayers induced by the OHE have also been observed. Our findings confirm the existence of the orbital Hall torques in Cr and provide an effective way to investigate the OHE.

Multiplexed MPC attitude control of a moving mass satellite using dual-rate piecewise affine model

This paper proposes a Multiplexed MPC algorithm for the dual-rate piecewise affine (PWA) model to control the attitude of a low-Earth-orbit (LEO) moving mass satellite. Although still facing an inherent inertial disturbance problem, the moving mass technology is a promising way to counter the strong aerodynamic torques in LEO. To make the satellite attitude fully actuated, a magnetorquer is used to cooperate with the moving mass system, resulting in a two-input control system. Through a strategy that updates inputs asynchronously, the proposed algorithm effectively balances the inertial disturbances caused by mass motions, the system's dynamic performance, and the controller's computational complexity. Error attitude kinematic and dynamic equations are derived, to convert the tracking problem into an equivalent regulation problem. The PWA approximation is used to transform the nonlinear attitude control equations described by error modified Rodrigues parameter to a linear state-space model for MPC design. Then, a new form of Multiplexed MPC, namely dual-rate PWA-MMPC, is developed for this dual-rate PWA model, which updates two control inputs at different rates. Despite only finding sub-optimal solutions to the original problem by stability analysis, this algorithm outperforms other control strategies through its ability to coordinate multiple inputs, deal with constraints, and reduce computational complexity. Hardware-in-the-loop simulations are conducted to demonstrate the effectiveness of the proposed methodology for the attitude control.

Effect of the Current Intensity and Inter-Electrode Distance in Surface Electrical Stimulation: A FEM Simulation Study.

In functional electric stimulation, variables such as electrode size, shape, and inter-electrodes distance can produce different neural and functional responses. In this work, a computational model combining FEM and MRG axon models is implemented to replicate two experimental studies that compare the effect of changing inter-electrode distance when applying FES to induce knee flexion. One work affirms that the stronger torque happens for greater distances, while the other obtain its maximum at lower distances. Using a simplified computational model gave another study perspective to understand why these two stimulation methodologies obtain different results. According to our results, an anodic stimulation occurs with greater current intensities and inter-electrode distances. This anodic effect can activate other nerve or motor points in the vicinity of the anode, explaining that more muscle fibers are recruited and generate an increased torque. Clinical Relevance - This work gives another view to understanding how the distance between electrodes affects neural activation, which has implications for optimizing clinical and exercise protocols using electrical stimulation techniques.

One among many: the enigmatic case of the Miocene mammal, Kolponomos newportensis

Abstract Kolponomos newportensis is an enigmatic Miocene mammal allied to stem Pinnipedimorpha. It has been suggested that Kolponomos fed on hard-shelled benthic marine invertebrates by using its mandible as a wedge to dislodge its prey from the sea bottom by means of strong pull and torque forces. This unique feeding style was thought to originate from a singular case of mosaic convergence in mandible biomechanics between Kolponomos and the sabretoothed cat Smilodon, which complied with similarly strong torque forces when grappling with prey. As such forces must have reflected on the cranium as well, we hypothesize that the convergence between Kolponomos and the sabretoothed cats could have affected its shape. To test this hypothesis, we looked for patterns of morphological convergence in cranial shape between Kolponomos and sabretoothed cats. We found that Kolponomos is not distinctly closer to Smilodon than a number of other pinnipeds. Yet, local areas of shape convergence with Smilodon are observed in the canine area and the posterior part of the cranium, that is where the bite applies and the temporalis muscle is located, respectively. These results indicate that the mosaic convergence present between the mandibles of Kolponomos and Smilodon is partially reflected in the cranium as well.

Finite element modeling of spin–orbit torques

Using a spin drift–diffusion model for coupled spin and charge transport, including the spin Hall effect and the inverse spin Hall effect, spin–orbit torques acting on the magnetization in heavy metal/ferromagnet bilayers are evaluated employing a finite element approach. The behavior of the resulting spin accumulation and torques is analyzed for different magnetization orientations of the ferromagnetic layer and varying thicknesses of the heavy metal layer. A strong damping-like torque component, consistent with experimental results, is observed. In addition, sub-ns switching simulations based on solving the Landau–Lifshitz–Gilbert equation are demonstrated.

Decoding the star forming properties of gas-rich galaxy pairs

ABSTRACT We extend the analysis of Bok et al. (2020) in which the H i content of isolated galaxies from the AMIGA (Analysis of the interstellar Medium in Isolated GAlaxies) sample and selected paired galaxies from ALFALFA (Arecibo Legacy Fast ALFA) were examined as a potential driver of galaxy location on the WISE (Wide-field Infrared Survey Explorer) mid-infrared SFR–M⋆ sequence. By further characterizing the isolated and pair galaxy samples, i.e. in terms of optical galaxy morphology, a more detailed and quantitative description of local galaxy environment by way of the local number density (η) and tidal strength (Q) parameters, star formation efficiency (SFE$_{\rm {H{\small {\rm ~I}}}}$), and H i integrated profile asymmetries, we present plausible pathways for the broadening of the pair sample H i deficiency distribution towards both high and low deficiencies compared to the narrower isolated galaxy sample distribution (i.e. σPAIRS = 0.34 versus σAMIGA = 0.28). We associate the gas-rich tail of the pair deficiency distribution with the highest Q values, large profile asymmetries, and low SFEs. From this, we infer that merger activity is enhancing gas supplies, as well as disrupting the efficiency of star formation, via strong gravitational torques. The gas-poor wing of the deficiency distribution appears to be populated with galaxies in denser environments (with larger η values on average), more akin to groups. Despite our gas-rich selection criterion, there is a small population of early-type galaxies in the pair sample, which primarily fall in the positive deficiency wing of the distribution. These results suggest that a combination of a denser galaxy environment, early-type morphology, and higher stellar mass is contributing to the broadening of the deficiency distribution towards larger deficiencies.

A survey of disc thickness and viscosity in circumbinary accretion: Binary evolution, variability, and disc morphology

ABSTRACTMuch of the parameter space relevant to the evolution of astrophysical circumbinary accretion discs remains unexplored. We have carried out a suite of circumbinary disc simulations surveying both disc thickness and kinematic viscosity, using both constant-ν and constant-α prescriptions. We focus primarily on disc aspect ratios between 0.1 and 0.033, and on viscosities between ν = 0.0005 and ν = 0.008 (in units of binary semimajor axis and orbital frequency), and specialize to circular equal-mass binaries. Both factors strongly influence the evolution of the binary semimajor axis: at ν = 0.0005, inspirals occur at aspect ratios ≲ 0.059, while at ν = 0.004 inspirals occur only at aspect ratios ≲ 0.04. Inspirals occur largely because of the increasingly strong negative torque on the binary by streams of material which lag the binary, with negligible contributions from resonant torques excited in the circumbinary disc. We find that reductions in accretion rate occur when simulations are initialized too far from the eventual quasi-steady state driven by interaction with the binary, rather than being intrinsically linked to the disc aspect ratio. We find not only that the cavity size increases as viscosity is decreased, but that thinner circumbinary discs become more eccentric. Our results suggest that supermassive black hole binaries should be driven, more rapidly than previous estimates, from ∼parsec separations to distances where gravitational waves drive their inspiral, potentially reducing the number of binaries observable by pulsar timing arrays.

Exchange-Torque-Triggered Fast Switching of Antiferromagnetic Domains.

The antiferromagnet is considered to be a promising hosting material for the next generation of magnetic storage due to its high stability and stray-field-free property. Understanding the switching properties of the antiferromagnetic (AFM) domain state is critical for developing AFM spintronics. By utilizing the magneto-optical birefringence effect, we experimentally demonstrate the switching rate of the AFM domain can be enhanced by more than 2 orders of magnitude through applying an alternating square-wave field on a single crystalline Fe/CoO bilayer. The observed extraordinary speed can be much faster than that triggered by a constant field with the same amplitude. The effect can be understood as the efficient suppression of the pinning of AFM domain walls by the strong exchange torque triggered by the reversal of the Fe magnetization, as revealed by spin dynamics simulations. Our finding opens up new opportunities to design the antiferromagnet-based spintronic devices utilizing the ferromagnet-antiferromagnet heterostructure.

Efficient orbital torque in polycrystalline ferromagnetic−metal/Ru/Al2O3 stacks: Theory and experiment

Recently emergent current-induced orbital torque is considered more effective for magnetization switching than the well-established spin-orbit torque. However, long-range orbital transport in polycrystalline films and the theory on orbital transport in polycrystalline heterostructures remain elusive. Here we report a large torque effect in $\mathrm{CoFeB}/\mathrm{Ru}/{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ polycrystalline stacks. The unfilled $d$-shell and small spin-orbit coupling in Ru provide an ideal platform for orbital generation and transport. The orbital current from the $\mathrm{Ru}/\mathrm{A}{\mathrm{l}}_{2}{\mathrm{O}}_{3}$ interface can go through a thick Ru layer, with a peak value at 7-nm-thick Ru, and then induces a strong torque effect in CoFeB. The torque efficiency increases unprecedentedly with increasing CoFeB layer thickness, leveling off at $\ensuremath{\sim}0.3$ for 12-nm-thick CoFeB. Theoretical analysis shows that the orbital transport in polycrystalline materials exhibits a unique random precession behavior, leading to a more efficient orbital transport than that in single crystals. Besides the fundamental significance, our findings advance the development of practical orbital torque devices.

Giant tunable spin Hall angle in sputtered Bi2Se3 controlled by an electric field

Finding an effective way to greatly tune spin Hall angle in a low power manner is of fundamental importance for tunable and energy-efficient spintronic devices. Recently, topological insulator of Bi2Se3, having a large intrinsic spin Hall angle, show great capability to generate strong current-induced spin-orbit torques. Here we demonstrate that the spin Hall angle in Bi2Se3 can be effectively tuned asymmetrically and even enhanced about 600% reversibly by applying a bipolar electric field across the piezoelectric substrate. We reveal that the enhancement of spin Hall angle originates from both the charge doping and piezoelectric strain effet on the spin Berry curvature near Fermi level in Bi2Se3. Our findings provide a platform for achieving low power consumption and tunable spintronic devices.

Systematic Modeling and Analysis of On-Board Vehicle Integrated Novel Hybrid Renewable Energy System with Storage for Electric Vehicles

The automobile industry and technology are putting a great significance in improving vehicles to become more fuel economical, but with incremental costs relative to conventional vehicle technologies; these new vehicles are electric vehicles (EV), plug-in hybrid electric vehicles (PHEV), and hybrid electric vehicles (HEV). However, their significant capabilities to reduce petroleum consumption and achieve efficiency over their life cycles offer economic benefits for customers, industry, carmakers, and policymakers. In this paper, an HEV concept based on renewable energy resources (RERs) is proposed. The proposed HEV design utilizes solar PV energy, wind energy, fuel cell, and a supercapacitor (PV + WE + FC + SC) which generates electrical energy via a proton exchange membrane (PEM) and an SC to cater for strong torque requirements. The vehicle incorporates a battery pack in conjunction with an SC for the power demands and an FC as the backup energy supply. An alternator connected to turbine blades runs by wind energy while the car is moving forward, which produces electricity through the alternator to charge the battery. The design aims to ensure zero carbon emission and improved energy efficiency, is lightweight, and incorporates in-wheel motors to eliminate the mechanical transmissions. Modeling and simulation were carried out for each subsystem using MATLAB® and Simulink® packages. ANSYS Fluent simulation was used to analyze wind energy. The standard analysis, e.g., pressure, velocity, and vector contour, were also considered while designing the final model. To regulate the power supply and demand, the selection of energy sources was controlled by a rule-based supervisory controller following a logical sequence that prioritizes energy sources with the SC as a source in-vehicle stop-and-go situations while the battery acts as the primary source, FC as a backup supply, and wind and solar power to recharge the battery. Solar charging is switched on automatically once the vehicle is parked, and the controller controls the energy flow from the alternator during that period.

Promoting effect of vegetation onthe initiation of landslides induced by typhoon rainstorms

Vegetation is widely used to prevent landslides worldwide. However, rainstorm-induced landslides frequently occur on vegetation-covered slopes during the typhoon season in the southeastern coast of China. The results of a wind tunnel test reveal the effect of typhoon-induced loads on a slope through vegetation. Under a wind speed of 17m/s, the wind load can increase the sliding force by over 10%. Strong typhoon-induced loads cause the vegetation to exert a strong torque on the soil via roots, resulting in crack development. These cracks provide paths for rainwater infiltration and increase the soil permeability coefficient by over 10-fold when the typhoon passes. Therefore, special attention should be paid to the potential impacts of vegetation, especially large trees, on slope stability.

Investigation: Cutting Transport Mechanism in Inclined Well Section under Pulsed Drilling Fluid Action

Due to gravity, drilling cuttings are easily accumulated in an inclined well section, ultimately forming a cuttings bed, which places the drill pipe under strong friction torque. In severe cases, this can cause dragging, stuck drills, and broken drill tools. Because conventional drilling fluids are difficult to prevent the formation of cuttings in inclined well sections, a method of carrying cuttings with the pulsed drilling fluid to improve wellbore cleanness is proposed. Experiments and numerical simulations are conducted to investigate the effects of cuttings bed transport velocity, cuttings size, cuttings height, drill pipe rotation speed, cuttings bed mass, and roughness height. The optimal pulse parameters are determined per their respective impact on cuttings transport concerning varied periods, amplitudes, and duty cycles of the pulsed drilling fluid. Compared to cuttings transport under the conventional drilling fluid flow rate, the pulsed drilling fluid produces the turbulent dissipation rate, increases cuttings transport velocity, and thus improves the wellbore clearance rate.

Current-Induced Spin Torques on Single GdFeCo Magnetic Layers.

Spintronics exploit spin-orbit coupling (SOC) to generate spin currents, spin torques, and, in the absence of inversion symmetry, Rashba and Dzyaloshinskii-Moriya interactions. The widely used magnetic materials, based on 3d metals such as Fe and Co, possess a small SOC. To circumvent this shortcoming, the common practice has been to utilize the large SOC of nonmagnetic layers of 5d heavy metals (HMs), such as Pt, to generate spin currents and, in turn, exert spin torques on the magnetic layers. Here, a new class of material architectures is introduced, excluding nonmagnetic 5d HMs, for high-performance spintronics operations. Very strong current-induced torques exerted on single ferrimagnetic GdFeCo layers, due to the combination of large SOC of the Gd 5d states and inversion symmetry breaking mainly engineered by interfaces, are demonstrated. These "self-torques" are enhanced around the magnetization compensation temperature and can be tuned by adjusting the spin absorption outside the GdFeCo layer. In other measurements, the very large emission of spin current from GdFeCo, 80% (20%) of spin anomalous Hall effect (spin Hall effect) symmetry is determined. This material platform opens new perspectives to exert "self-torques" on single magnetic layers as well as to generate spin currents from a magnetic layer.

Design, Fabrication, and Testing of a Full-Scale HTS Coil for a 10 MW HTS Wind Power Generator

The authors have proposed a performance evaluation system (PES) for large-scale high temperature superconducting (HTS) wind power generators, which produces strong electromagnetic force and high torque due to the high excitation current and the high magnetic load of the machine, based on the computer simulation results. The PES can physically test the structural stability of HTS coils and armatures against high torque and the effect of the magnetic field before mounting the HTS coil on the generator. This paper deals with the design, fabrication, and performance testing of a full-scale HTS coil to be installed in the PES, a performance analysis system for a 10 MW HTS wind power generator. The HTS coil with metal-insulation consists of four racetrack-type single coils with 310 turns per layer. The manufactured HTS coil was tested at 77 K with and without an iron-core. As a result, the critical currents of the tested HTS coils with and without the iron-core were 90 A and 106 A, respectively. Compared to the simulation results, it was found that the magnitude of the magnetic field was the same. These results will be effectively used to study and fabricate high magnetic field coils for HTS applications, as well as the PES being fabricated.

Electron-magnon spin conversion and magnonic spin pumping in an antiferromagnet/heavy metal heterostructure

We study the exchange between electron and magnon spins at the interface of an antiferromagnet and a heavy metal at finite temperatures. The underlying physical mechanism is based on spin torque associated with the creation/annihilation of thermal magnons with right-hand and left-hand polarization. The creation/annihilation process depends strongly on the relative orientation between the polarization of the electron and the magnon spins. For a sufficiently strong spin transfer torque (STT), the conversion process becomes nonlinear, generating a nonzero net spin pumping current in the AFM that can detected in the neighboring metal layer. Applying an external magnetic field renders possible the manipulation of the STT driving thermal spin pumping. Our theoretical results are experimentally feasible and are of a direct relevance to antiferromagnet-based spintronic devices.

Strong spin-orbit torque effect on magnetic defects due to topological surface state electrons in Bi2Te3

We investigate the spin-orbit torque exerted on the magnetic moments of the transition-metal impurities Cr, Mn, Fe and Co, embedded in the surface of the topological insulator Bi$_{2}$Te$ _{3} $, in response to an electric field and a consequent electrical current flow in the surface. The multiple scattering problem of electrons off impurity atoms is solved by first-principles calculations within the full-potential relativistic Korringa-Kohn-Rostoker (KKR) Green function method, while the spin-orbit torque calculations are carried out by combining the KKR method with the semiclassical Boltzmann transport equation. We analyze the correlation of the spin-orbit torque to the spin accumulation and spin flux in the defects. We compare the torque on different magnetic impurities and unveil the effect of resonant scattering. In addition, we calculate the resistivity and the Joule heat as a function of the torque in these systems. We predict that the Mn/Bi$_{2}$Te$_{3}$ is optimal among the studied systems.

Effect of seed and interlayer Pt thickness on spin-orbit torque efficiency in Co/Pt multilayer with perpendicular magnetic anisotropy

As-deposited [Co/Pt] multilayers show strong perpendicular magnetic anisotropy (PMA) and spin-orbit torque (SOT). However, such structures require properly textured Pt (111) seed layers and optimized interlayer Pt thicknesses in order to maximise both PMA and SOT efficiency. In this work, the interplay of seed and interlayer Pt thickness on PMA and SOT efficiency in Ta/Pt/[Co/Pt]3/Co/Ta multilayers was studied. Using the harmonic lock-in method, the SOT damping- and field-like efficiencies were determined, with corrections for current shunting as well as the planar Hall effect. Our measurements show that the corrected effective SOT efficiencies are at least twice as large as the uncorrected values, with damping-like efficiency of up to ∼22 Oe per 1010 A m−2, which scales inversely with the Pt seed and interlayer thicknesses due to screening of the spin current originating from the high-resistivity bottom -Ta layer. The choice of Pt seed and interlayer thicknesses is a compromise between PMA and SOT efficiency of the device.