Orbital torque in magnetic bilayers Lee, Dongjoon; Go, Dongwook; Park, Hyeon-Jong ...
Nature communications,
11/2021, Letnik:
12, Številka:
1
Journal Article
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The orbital Hall effect describes the generation of the orbital current flowing in a perpendicular direction to an external electric field, analogous to the spin Hall effect. As the orbital current ...carries the angular momentum as the spin current does, injection of the orbital current into a ferromagnet can result in torque on the magnetization, which provides a way to detect the orbital Hall effect. With this motivation, we examine the current-induced spin-orbit torques in various ferromagnet/heavy metal bilayers by theory and experiment. Analysis of the magnetic torque reveals the presence of the contribution from the orbital Hall effect in the heavy metal, which competes with the contribution from the spin Hall effect. In particular, we find that the net torque in Ni/Ta bilayers is opposite in sign to the spin Hall theory prediction but instead consistent with the orbital Hall theory, which unambiguously confirms the orbital torque generated by the orbital Hall effect. Our finding opens a possibility of utilizing the orbital current for spintronic device applications, and it will invigorate researches on spin-orbit-coupled phenomena based on orbital engineering.
Controlling magnetic states by a small current is essential for the next‐generation of energy‐efficient spintronic devices. However, it invariably requires considerable energy to change a magnetic ...ground state of intrinsically quantum nature governed by fundamental Hamiltonian, once stabilized below a phase‐transition temperature. Here, it is reported that, surprisingly, an in‐plane current can tune the magnetic state of the nanometer‐thin van der Waals ferromagnet Fe3GeTe2 from a hard magnetic state to a soft magnetic state. It is a direct demonstration of the current‐induced substantial reduction of the coercive field. This surprising finding is possible because the in‐plane current produces a highly unusual type of gigantic spin–orbit torque for Fe3GeTe2. In addition, a working model of a new nonvolatile magnetic memory based on the principle of the discovery in Fe3GeTe2, controlled by a tiny current, is further demonstrated. The findings open up a new window of exciting opportunities for magnetic van der Waals materials with potentially huge impact on the future development of spintronic and magnetic memory.
Substantial coercivity reduction by the current, larger at least by two orders of magnitude than those in previous reports, is found in the van der Waals ferromagnet Fe3GeTe2. It is theoretically shown to arise from an unusual type of gigantic spin–orbit torque, which itself is directly related to its special symmetries, large Berry curvature, and band topology. A working model of a new robust nonvolatile magnetic memory based on Fe3GeTe2, controlled by a much smaller current, is also produced.
Recent extensive research on flexible electronics has led to the development of various flexible sensors. In particular, sensors inspired by the slit organs of a spider, which utilize cracks in a ...metal film to measure strain, have garnered considerable interest. This method exhibited significantly high sensitivity, repeatability, and durability in measuring strain. In this study, a thin-film crack sensor was developed using a microstructure. The results exhibited its ability to simultaneously measure the tensile force and pressure in a thin film, further expanding its applications. Furthermore, the strain and pressure characteristics of the sensor were measured and analyzed using an FEM simulation. The proposed method is expected to contribute to the future development of wearable sensors and artificial electronic skin research.
A systematic domain reduction strategy is proposed to mitigate the high computational cost of performing a large-eddy simulation (LES) for predicting underwater radiated noise from a marine ...propeller. The key concept of this strategy is to determine where detailed analysis is necessary beforehand and accordingly reduce the computational domain. The strategy comprises the following steps: (1) performing a Reynolds-averaged Navier–Stokes (RANS) simulation in the full domain, including the entire hull; (2) quantitatively analyzing the region affected by the propeller; (3) reducing the domain to encompass most of the propeller’s effect; and (4) conducting an LES in the reduced domain, using the flow field from the RANS simulation as an inlet boundary condition. By implementing the proposed strategy, the LES domain length is reduced by up to twice the propeller diameter in the upstream direction from the propeller, representing only 7% of the hull’s total length. The strategy’s effectiveness is validated by comparing the simulation results with the experimental data obtained at the Korea Research Institute of Ships and Ocean.
•An efficient LES method for underwater radiated noise from a propeller is developed.•A systematic domain reduction strategy is proposed to reduce the computational cost for LES.•The effectiveness of the proposed method for underwater radiated noise is validated.
Efforts to enhance greenhouse gas (GHG) emission reduction in East Asia play a pivotal role on both global and regional scales in advancing climate mitigation strategies. This study aimed to better ...constrain anthropogenic CO2 emission estimates by expanding the network of near-surface in-situ stations for CO2 observations across South Korea. To achieve an optimal CO2 network design, we conducted an Observing System Simulation Experiment (OSSE) coupled with the Stochastic Lagrangian Transport model (STILT), utilizing meteorological data from the Korean Integrated Model (KIM). Our inversion setup incorporated two CO2 emission datasets with a 0.1o resolution: EDGAR v6 for prior emissions and GRACED for truth emissions. A uniform model-mismatch error of 3 ppm was introduced across sites. The effectiveness of the existing five in-situ stations, termed the base network, in South Korea was evaluated to gauge their ability to constrain CO2 surface flux estimates. However, the findings revealed a reduction in flux uncertainty of only 29.2%, which fell short of the desired uncertainty reduction goal. In this base network, the Lotte World Tower (LWT: 37.5126°E, 127.1025°E) in Seoul and the Anmyeondo (AMY: 36.538576° N, 126.330071° E) site in Taean county stood as major contributors, with estimated reductions of 17.48% and 6.35%, respectively. Consequently, we proposed and developed an extended network, identifying seven candidate sites based on consideration of logistical factors, existing infrastructures, and proximity to the emission source regions. An incremental optimization scheme ranked their contributions, resulting in an additional 25% reduction, bringing the total to 54.13%. However, it is noteworthy that diminishing returns (ranging from 13% to less than 0.1%) were observed with an increase in station count mainly due to the possibility that adding a station earlier in the sequence might render subsequent stations redundant. Despite this, the proposed CO2 network successfully reduced uncertainty in emissions, narrowing the gap with the objectives of the Global Greenhouse Gas Watch (G3W).
•Designing CO2 near-surface observation network over South Korea.•New stations selected considering logistic factors, existing infrastructures, and proximity to emission sources.•The base network was able to reduce 29.18% of the uncertainty in CO2 emissions.•Extending network, by adding new seven candidate sites, led to a total uncertainty reduction of 54.13%.
Owing to the continuous interest on high-speed railway trains, research on the brake disc made of ferritic cast steel with high strength and toughness, and the manufacturability of complicated ...cooling fins has been conducted. In acicular ferrite, Ti is a major element; however, studies on the effect of Ti composition on the mechanical and impact properties are limited to a Ti content of up to 0.05 wt%. In this study, the microstructure and mechanical properties of high-speed railway brake disc steel material with 0–0.12 wt% Ti were investigated. The specimens were subjected to the same quenching–tempering heat treatment, in which acicular ferrite formation was observed by optical microscopy, scanning electron microscopy, electron backscatter diffraction (EBSD), electron probe microanalyzer, and transmission electron microscopy. Ferrite blocks, such as acicular ferrite, granular bainite, bainitic ferrite, and polygonal ferrite, were characterized in detail and quantitatively analyzed by EBSD. For different Ti contents, ferrites of various morphologies were noted. Moreover, the types of precipitates were determined to be cementite, Cr-rich carbide, V-rich carbide, and Ti-rich carbide. The highest hardness, impact toughness, and strength were measured with the addition of 0.06 wt% Ti. The crack propagation mode in the impact specimen was observed using fracture surface analysis. In addition, the relationship between the microstructure and mechanical properties, such as strength, toughness, and hardness, was discussed based on the alloying Ti content. In this study, the effect of acicular ferrite and precipitates on toughness in ferrite casting steel was confirmed, and the optimal Ti content was confirmed.
The orbital Hall effect
refers to the generation of electron orbital angular momentum flow transverse to an external electric field. Contrary to the common belief that the orbital angular momentum is ...quenched in solids, theoretical studies
predict that the orbital Hall effect can be strong and is a fundamental origin of the spin Hall effect
in many transition metals. Despite the growing circumstantial evidence
, its direct detection remains elusive. Here we report the magneto-optical observation of the orbital Hall effect in the light metal titanium (Ti). The Kerr rotation by the orbital magnetic moment accumulated at Ti surfaces owing to the orbital Hall current is measured, and the result agrees with theoretical calculations semi-quantitatively and is supported by the orbital torque
measurement in Ti-based magnetic heterostructures. This result confirms the orbital Hall effect and indicates that the orbital angular momentum is an important dynamic degree of freedom in solids. Moreover, this calls for renewed studies of the orbital effect on other degrees of freedom such as spin
, valley
, phonon
and magnon
dynamics.
•The response of microbial communities in soils treated with 0.1–1mgg−1 soil Ag-GO was determined.•Ag-GO significantly lowered C-cycling enzyme activity and inhibited nitrification.•Ag-GO decreased ...the relative abundance of Acidobacteria and Cyanobacteria while it increased that of Firmicutes.•Ag-GO can negatively affect soil microbial activity associated with C and N cycling and alter bacterial community composition.
Due to the application of silver-graphene oxide (Ag-GO) in diverse fields, it is important to investigate its potential impacts on the environment including soils. In this study, the response of microbial communities in soils treated with Ag-GO synthesized by glucose reduction was determined by analyzing enzyme activities, biomass, and inorganic N concentrations and by pyrosequencing. In soils treated with 0.1–1mg Ag-GO g−1 soil, the activities of β-glucosidase, cellobiohydrolase, and xylosidase decreased up to 80% and NO3− concentration decreased up to 82% indicating inhibited nitrification. Within the bacterial community, the relative abundance of Acidobacteria and Cyanobacteria in soils treated with Ag-GO were lower than that in control soil. Meanwhile, the relative abundance of AD3 and Firmicutes tended to increase under Ag-GO treatments. These changes in bacterial community composition reflected lowered activities associated with C and N cycling. On the other hand, microbial biomass showed no distinct change in response to Ag-GO treatment. Our study can serve as important basis in establishing guidelines for regulating the release of nanocomposites such as Ag-GO to the soil environment.
A device‐free human counting (DFC) algorithm that uses fine‐grained subcarrier information from WiFi devices, called channel state information (CSI), to count the number of people in indoor ...environments is proposed. The DFC algorithm extracts the features of average attenuation and variation of CSI amplitudes caused by human motions, and puts the features into a training process to improve the counting accuracy. Through a bootstrapping process, the DFC can estimate the number of people standing in the middle of a WiFi link by constructing a probability model with the CSI signals at a receiver side. With this human counting capability, the DFC can support the efficient monitoring and automatic control of electrical devices (e.g. air conditioner, heater, bulb, and beam projector) indoors. Through a real implementation and experiments, it is shown that the DFC algorithm outperforms the state‐of‐the‐art DFC algorithm based on RSSI in indoor environments with human mobility. For a dynamic‐target case in a meeting room, for example, DFC can predict the number of people in an indoor space with an accuracy about 98% at best.
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