Magnetic Unit Research Articles

Low-Temperature Glassy Behavior of Sr2Ni3(C2O4)3(OH)4·3H2O with Frustrated Spin Hexamers.

In this paper, we studied the synthesis, crystal structure, magnetism, and memory effect of a spin hexamer compound Sr2Ni3(C2O4)3(OH)4·3H2O. The basic magnetic unit of this compound is a ringed spin hexamer (Ni6 cluster). These Ni6 clusters are connected by an oxalate group, constituting a two-dimensional framework along the ab plane. With decreasing temperature, three anomalies are detected in susceptibility curves, corresponding to the formation of short-range spin correlation around 42.5 K, the onset of an antiferromagnetic ordering at 21.4 K, and a reentrant cluster spin-glass state below 12 K. A strong spin frustration is demonstrated with a frustrated factor f ∼ 11. The dominant exchange interactions are J1/kB = -17.1 K and J2/kB = -81.1 K, evaluated by exact diagonalization analysis with an isolated Ni6 cluster model. A nonequilibrium dynamics study of magnetic memory effect indicates the evolution of several intermediate metastable states.

An isolated organ feasibility study of deformable self-assembled magnetic anastomosis rings for esophageal stenosis anastomosis

Magnetic compression anastomosis (MCA) for esophageal stenosis requires the insertion of magnets through two channels, transoral and transgastrostomy. Herein, we designed a Y-Z deformable self-assembled magnetic anastomosis ring (Y-Z DSAMAR) for esophageal stricture anastomosis through the transoral passage only. We introduce a Y-Z DSAMAR and verify its feasibility for single-access esophageal stenosis anastomosis in isolated organs. We procured esophagi from 10 pigs. Next, we ligated the middle part of these esophagi with 7 − 0 silk to prepare an esophageal stenosis model. The linear Y-Z DSAMAR completed the deformation self-assembly and transitioned from its initial linear shape to a circular one while passing through the esophageal stenosis. The operation time, the success rate of the deformation self-assembly of Y-Z DSAMARs, and the successful MCA for esophageal stenosis were recorded. We successfully obtained a trapezoidal magnetic unit. Ten such magnetic units can self-assemble into a ring after the hard guide wire is withdrawn. The success rates for both self-assembly deformation and esophageal stenosis anastomosis were 93.33%, while that for esophageal stenosis anastomosis with successful deformation was 100%. Y-Z DSAMARs exhibit remarkable deformation-controllable characteristics. Further optimization of the operational procedure and verification through animal experiments are needed before they can be clinically applied.

Competing magnetic states on the surface of multilayer ABC-stacked graphene

We study interaction-mediated magnetism on the surface of ABC-multilayer graphene driven by its zero-energy topological flat bands. Using the random-phase approximation, we treat onsite Hubbard repulsion and find multiple competing magnetic states, due to both intra- and intervalley scattering, with the latter causing an enlarged magnetic unit cell. At half-filling and when the Hubbard repulsion is weak, we observe two different ferromagnetic orders. Once the Hubbard repulsion becomes more realistic, new ferrimagnetic orders arise with distinct incommensurate intra- or intervalley scattering vectors depending on interaction strength and doping, leading to a multitude of competing magnetic states. Published by the American Physical Society 2024

Kernel polynomial method for linear spin wave theory

Calculating dynamical spin correlations is essential for matching model magnetic exchange Hamiltonians to momentum-resolved spectroscopic measurements. A major numerical bottleneck is the diagonalization of the dynamical matrix, especially in systems with large magnetic unit cells, such as those with incommensurate magnetic structures or quenched disorder. In this paper, we demonstrate an efficient scheme based on the kernel polynomial method for calculating dynamical correlations of relevance to inelastic neutron scattering experiments. This method reduces the scaling of numerical cost from cubic to linear in the magnetic unit cell size.

Design of magneto-inductive waveguide in 2-d magnetic metamaterial structure for wireless power transfer and near-field communications

<p>Recently, significant research has been conducted on magnetic metamaterials that exhibit negative permeability and operate within the GHz and MHz frequency ranges. These metamaterial structures can be utilized to improve the efficiency of near-field wireless power transfer systems, subterranean communication, and position sensors. However, in most cases, they are only designed to work for a single application. This study focuses on examining the transmission of magneto-inductive waves in magnetic metamaterial structures with ordered arrangements. This structure can be used simultaneously for wireless power transfer and near-field communications. The unit cell is formed by a spiral with five turns that is implanted on a FR-4 substrate. An external capacitor was used to regulate the resonant frequency of the magnetic metamaterial unit cell. The properties of magneto-inductive waves, including reflection, transmission response, and field distribution on the waveguide, have been extensively computed and simulated. The obtained results indicate that both 1-dimensional and 2-dimensional magnetic metamaterial configurations possess the ability to conduct electromagnetic waves and propagate magnetic field energy at a frequency of 13.56 MHz. The straight and cross path configurations were also investigated to identify the optimal configuration on the 2-dimensional metamaterial slab.</p>

A machine learning approach for the design optimization of a multiple magnetic and inertial sensors wearable system for the spine mobility assessment

BackgroundRecently, magnetic and inertial measurement units (MIMU) based systems have been applied in the spine mobility assessment; this evaluation is essential in the clinical practice for diagnosis and treatment evaluation. The available systems are limited in the number of sensors, and neither develops a methodology for the correct placement of the sensors, seeking the relevant mobility information of the spine.MethodsThis work presents a methodology for analyzing a system consisting of sixteen MIMUs to reduce the amount of information and obtain an optimal configuration that allows distinguishing between different body postures in a movement. Four machine learning algorithms were trained and assessed using data from the range of motion in three movements (Mov.1—Anterior hip flexion; Mov.2—Lateral trunk flexion; Mov.3—Axial trunk rotation) obtained from 12 patients with Ankylosing Spondylitis.ResultsThe methodology identified the optimal minimal configuration for different movements. The configuration showed good accuracy in discriminating between different body postures. Specifically, it had an accuracy of 0.963 ± 0.021 for detecting when the subject is upright or bending in Mov.1, 0.944 ± 0.038 for identifying when the subject is flexed to the left or right in Mov.2, and 0.852 ± 0.097 for recognizing when the subject is rotated to the right or left in Mov.3.ConclusionsOur results indicate that the methodology developed results in a feasible configuration for practical clinical studies and paves the way for designing specific IMU-based assessment instruments.Trial registration: Study approved by the Local Ethics Committee of the General Hospital of Mexico “Dr. Eduardo Liceaga” (protocol code DI/03/17/471).

Design, dynamic modeling and testing of a novel MR damper for cable-stayed climbing robots under wind loads

To increase the adaptability of bridge construction equipment in high-altitude settings, this study examines a magnetorheological (MR) damper designed for cable-stayed climbing robots. Initially, a novel damper incorporating a spring-MR fluid combination and three magnetic circuit units is developed. A robot-cable-wind coupling dynamic model is subsequently formulated via Hamilton’s principle, based on force analysis. The simulation results indicate that the damper’s maximum output force is 204.60 N, with optimal working currents of 0.2 A (Force 4) and 0.4 A (Force 7). To verify the analysis, testing is conducted using an MR damper. The results reveal an average relative error of 4.60% for the actual output damping force. When mounted on the robot, the climbing speed range, average relative error, and maximum relative error are controlled within 0.66 mm/s, 0.78% and 2.5%, respectively. This approach allows for the rapid selection of suitable working currents and markedly enhances the climbing stability of the robot.

Identification of Gold targets using airborne geophysics and remote sensing data in part of northcentral Nigeria

The exploration and utilization of economic mineral deposits are of paramount importance in driving the prosperity and progress of nations across the globe. An integrative approach of integrating aeromagnetic, airborne-radiometric, and remote-sensing methods was employed to assess gold mineralization zones within Paiko town in Niger state, northcentral Nigeria. Airborne-radiometric and remote-sensing datasets were utilized to map subsurface structures, lithological units, and hydrothermal alteration zones. The investigation delineated three major tectonic events along different directions: the ENE-WSW (D1) trending tectonic event, the WNW-ESE (D2) trending tectonic event, and NW-SE (D3) trending structural deformation event. The three deformation phases signify unique magnetic unit boundaries, lithological contacts, veins, and veinlets intrusions. These structures were interpreted as potential pathways for mineralization fluids. Moreover, the presence of high potassium-rich zones with low thorium/potassium ratio anomalies indicated potassium enrichments associated with sericite mica and K-feldspar minerals. The study also mapped various alterations of ferrous silicates, holding the potential to host gold and copper deposits, as well as endoskarn, epidot/chlorite/amphibole alterations, and phyllic minerals. Depth estimates derived from magnetic source parameters imaging techniques revealed that the mineralization targets in the area are relatively shallow, with depths ranging from the near-surface to less than 100 m. The delineation of mineralization zones in the study area convincingly demonstrates the effectiveness of integrating airborne geophysical and remote sensing data for exploring, developing, and managing subsurface mineral resources. This approach provides valuable insights into gold mineralization's presence, distribution, and characteristics, facilitating informed decision-making in mineral resource exploration and utilization.

Sensitivity analysis of an inertial calibration method: Influence of leg position on 3D knee kinematics

BackgroundInertial systems are increasingly used to analyze human motion, especially for gait analyses and in clinical settings. Calibration methods for these systems are designed for ease of implementation, and previous studies have shown that they can provide accurate knee kinematics in the sagittal plane. However, the reason of their lack of accuracy in the other planes (i.e., transverse and frontal) remain unknown. Research questionThis study aimed to evaluate the sensitivity of one posture of a double-pose calibration method to analyse 3D knee kinematics during gait with two magnetic inertial measurement units (MIMU). This method consists of a standing posture and a posture with the leg stretched forward in the sagittal plane, which together define the sagittal plane. Our hypothesis was that a change in the definition of the sagittal plane during the calibration process was likely to affect the assessment of knee kinematics in the frontal and transverse planes. MethodsTen healthy participants wearing the KneeKG system and two MIMU completed the calibration process in five different leg positions (0°, 3°, 5°, 10° or 15° from the sagittal plane) for the second calibration posture. After static calibration, the participants walked on an instrumented treadmill at a speed of 1.1 m/s and 3D knee kinematics were calculated using the five different calibration conditions. ResultsMean absolute difference (MAD) between the swing-phase peak value of the curve corresponding to the leg in the sagittal plane (0° shift from this plane) when performing the second calibration posture and each of the other curves was 0.20–0.46° for knee flexion, 1.67–2.90° for adduction, and 0.72–1.46° for external rotation. MAD of the swing-phase peak value in the frontal plane was correlated (R2=0.81) with the angulation of the femur in the sagittal plane during calibration. SignificanceAn angular shift from the sagittal plane when performing a double-pose calibration method induces a minimal influence on the knee flexion/extension but larger influences on secondary knee motions.

High-precision spatial measurement method of accelerator pre-alignment based on multiple total stations

Abstract With the development of accelerator technology, the scale of accelerators is becoming larger, ranging from hundreds of meters to several kilometers. For stable operation of accelerators, high-precision alignment, positioning, and installation are crucial. Installing all equipment inside the tunnel poses safety risks as personnel would be in a closed environment with potential radiation exposure for prolonged periods. To address the challenges of long adjustment and maintenance periods inside the tunnel due to the installation of equipment for large-scale accelerators, most accelerator devices under construction or in research have pre-alignment assemblies. Each assembly consists of a certain number of magnets distributed on girders. The magnets in one unit are pre-aligned with high precision in the laboratory and then transported to the tunnel. Aligning the entire magnet girder can significantly improve installation efficiency inside the tunnel. To meet the pre-alignment accuracy requirement of 10 μm in the horizontal and vertical directions for the magnet units in the high energy photon source (HEPS) storage ring, a system for high-precision pre-alignment of accelerator units using four total stations for angle observation has been designed in this paper. By employing different instrument layout configurations and incorporating reliable distance benchmarks, high-precision pre-alignment of the magnet are achieved. By arranging targets and utilizing recognition for automatic targeting, real-time point calculations during pre-alignment enhance efficiency. Subsequently, based on this system, pre-alignment simulation calculations and experimental verification of eight magnet focusing–defocusing units in the HEPS storage ring are conducted and ultimately realizing the 10 μm transverse and vertical pre-alignment measuring error within the units. This method, based on high-precision measurements in a small-scale space, reduces the period required for personnel on-site and improves pre-alignment efficiency. It also provides a reference for pre-alignment of multiple magnet units in large accelerators such as the Southern Advanced Photon Source and Circular Electron Positron Collider.

UWB distance estimation errors in (non-)line of sight situations within the context of 3D analysis of human movement

Abstract Integrated Ultrawideband (UWB) and Magnetic Inertial Measurement Unit (MIMU) sensors are becoming popular for indoor localization applications, as a higher accuracy can be achieved than with just MIMU sensors. These integrated sensors could extend stability and accuracy in the field of 3D analysis of human movement (3D AHM) if they can deliver position estimates with an accuracy close to 1 cm. Achieving this high accuracy of 1 cm remains challenging, with most studies reporting position estimation errors around 5 cm, often due to Non-Line of Sight (NLOS) conditions and systematic UWB sensor distance estimation errors. Studying the distance error characteristic of UWB in situations of 3D AHM is essential to deal with these errors. While research on UWB distance errors in Line of Sight (LOS) and NLOS situations exists, few studies focus on the NLOS errors caused by the human body and were not in the relevant scenarios of 3D AHM. Therefore, this article examines UWB sensor performance and distance error characteristics in LOS and NLOS situations typical for the 3D AHM. Both the LOS and NLOS situations were studied in the typical 3D AHM distance range of 0.2 m to 2 m. The NLOS situations were studied first with a human subject as NLOS causing object and then with simulated human body segments (PVC pipes filled with water) of varying diameters. In LOS situations, consistent systematic bias errors were observed, along with incidental errors at specific positions in the room. In NLOS scenarios caused by the human and simulated body segments, a consistent and reproducible overestimation of distances was found. The reproducibility of these errors based on relative node and object positions suggests that systematic mitigation methods could significantly reduce errors, enabling more accurate and reproducible 3D human movement analysis.

Meta Analysis of the Effect of Applying the Problem Based Learning Model in Physics Learning to Improve Students' Ability to Solve Problems

The meta-analysis method in this research was used to determine how problem-based learning activities influence problem-solving abilities. Analysis is carried out based on material units and levels/classes. Based on the results of the analysis, it was found that the mechanical material unit had an effect size of 0.83 in the high category, for the electric magnetic material unit it had an effect size value of 1.12 in the very high category, for the optical wave material unit it had an effect size of 1.66 with very high category, for thermodynamic material units it has an effect size of 1.41 in the very high category, and for fluid material units it has an effect size of 1.56 in the very high category. Then for class X it has an effect size of 1.19 in the very high category, for class XI it has an effect size of 1.35 in the very high category and for class In conclusion, for the optical wave material unit, it has an effect size of 1.81 which has a very high influence on students' ability to solve problems and for class XI level it has an effect size of 1.35 which has a very high influence on students' ability to solve problems.

Unique magnetic structure of the vdW antiferromagnet VBr3

VBr3 is a van der Waals antiferromagnet below the Néel temperature of 26.5 K with a saturation moment of 1.2 µB/f.u. above the metamagnetic transitions detected in the in-plane and out-of-plane directions. To reveal the AFM structure of VBr3 experimentally, we performed a single-crystal neutron diffraction study on a large high-quality crystal. The collected data confirmed a slight monoclinic distortion of the high-temperature rhombohedral structure below 90 K. The magnetic structure was, nevertheless, investigated within the R-3 model. The antiferromagnetic structure propagation vector k = (1, 0, ½) was revealed. In an attempt to determine the magnetic structure, 72 non-equivalent magnetic reflections were recorded. The experimental data were confronted with the magnetic space groups dictated by the R-3 lattice symmetry and propagation vector. The best agreement between the experimental data and the magnetic structure model was obtained for the space group P-1.1′_c. The magnetic unit cell of the proposed unique antiferromagnetic structure with periodicity 6c is built from two identical triple layers antiferromagnetically coupled along the c axis. Each triple layer comprises a Néel antiferromagnetic monolayer sandwiched between two antiferromagnetically coupled ferromagnetic monolayers.

Harvesting Magneto-Acoustic Waves Using Magnetic 2D Chromium Telluride (CrTe3).

A vast majority of electrical devices have integrated magnetic units, which generate constant magnetic fields with noticeable vibrations. The majority of existing nanogenerators acquire energy through friction/mechanical forces and most of these instances overlook acoustic vibrations and magnetic fields. Magnetic two-dimensional (2D) tellurides present a wide range of possibilities for devising a potential flexible energy harvester. 2D chromium telluride (2D CrTe3) is synthesized, which exhibits ferromagnetic behavior with a higher T c of ≈224 K. The structure exhibits stable high remnant magnetization, making 2D CrTe3 a potential material for harvesting magneto-acoustic waves. A magneto-acoustic nanogenerator (MANG) is fabricated and the basic mechanical stability and sensitivity of the device with change in load conditions are tested. A high surface charge density of 2.919 mC m-2 is obtained for the device. The thermal strain created in the lattice structure is examined using in-situ Raman spectroscopy. The magnetic anisotropy energy (MAE) responsible for long-range FM ordering is calculated by theoretical modelling with insights into opening of electronic bandgap which enhances the flexoelectric effects. The MANG can be a potential NG to synergistically tap into the magneto-acoustic vibrations generated from the frequency changes of a vibrating device such as loudspeakers.

Enumeration of Spin-Space Groups: Toward a Complete Description of Symmetries of Magnetic Orders

Symmetries of three-dimensional periodic scalar fields are described by 230 space groups (SGs). Symmetries of three-dimensional periodic (pseudo)vector fields, however, are described by the spin-space groups (SSGs), which were initially used to describe the symmetries of magnetic orders. In SSGs, the real-space and spin degrees of freedom are unlocked in the sense that an operation could have different spatial and spin rotations. SSGs give a complete symmetry description of magnetic structures and have natural applications in the band theory of itinerary electrons in magnetically ordered systems with weak spin-orbit coupling. , a concept raised recently that belongs to the symmetry-compensated collinear magnetic orders but has nonrelativistic spin plitting, is well described by SSGs. Because of the vast number and complicated group structures, SSGs have not yet been systematically enumerated. In this work, we exhaust SSGs based on the invariant subgroups of SGs, with spin operations constructed from three-dimensional (3D) real representations of the quotient groups for the invariant subgroups. For collinear and coplanar magnetic orders, the spin operations can be reduced into lower-dimensional real representations. As the number of SSGs is infinite, we consider only SSGs that describe magnetic unit cells up to 12 times crystal unit cells. We obtain 157 289 noncoplanar, 24 788 coplanar-noncollinear, and 1421 collinear SSGs. The enumerated SSGs are stored in an online database with a user-friendly interface. We develop an algorithm to identify SSGs for realistic materials and find SSGs for 1626 magnetic materials. We also discuss several potential applications of SSGs, including the representation theory, topological states protected by SSGs, structures of spin textures, and refinement of magnetic neutron diffraction patterns using SSGs. Our results serve as a solid starting point for further studies of symmetry and topology in magnetically ordered materials. Published by the American Physical Society 2024

Tailored Magnetic Spatial Confinement with Enhanced Polarization and Magnetic Response for Electromagnetic Wave Absorption.

For materials with coexisting phases, the transition from a random to an ordered distribution of materials often generates new mechanisms. Although the magnetic confinement effect has improved the electromagnetic (EM) performance, the transition from random to ordered magnetic confinement positions remains a synthetic challenge, and the underlying mechanisms are still unclear. Herein, precise control of magnetic nanoparticles is achieved through a spatial confinement growth strategy, preparing five different modalities of magnetic confined carbon fiber materials, effectively inhibiting magnetic agglomeration. Systematic studies have shown that the magnetic confinement network can refine CoNi NPs size and enhance strong magnetic coupling interactions. Compared to CoNi@HCNFs on the hollow carbon fibers (HCNFs) outer surface, HCNFs@CoNi constructed on the inner surface induce stronger spatial charge polarization relaxation at the interface and exhibit stronger magnetic coupling interactions at the inner surface due to the high-density magnetic coupling units at the micro/nanoscale, thereby respectively enhancing dielectric and magnetic losses. Remarkably, they achieve a minimum reflection loss (RLmin) of -64.54dB and an absorption bandwidth of 5.60GHz at a thickness of 1.77mm. This work reveals the microscale mechanism of magnetic confinement-induced different polarization relaxation and magnetic response, providing a new strategy for designing magnetic materials.

Research on the optimization methods of common points layout for survey and alignment of particle accelerators

As a fourth-generation synchrotron light source based on a diffraction-limited storage ring, Hefei Advanced Light Facility (HALF) puts forward higher requirements for the alignment accuracy of the main components. Aggregated common points result in a loss of accuracy during the coordinate transformation required by accelerator alignment. To address this challenge, we proposed two methods: “aggregated points centralization (APC)" and “uniformity-weighted algorithm (UWA)" according to different usage scenarios. APC combines uniformity with the K-means algorithm to enhance the accuracy of coordinate transformation while reducing the number of common points. UWA calculates the uniformity in different directions and assigns weights to common points, reducing the accuracy loss. Simulations demonstrate that these two methods have strong superiority and stability with significantly improved accuracy. Applications of these 2 methods in the magnet unit pre-alignment experiment and tunnel network measurement show promising results. APC in pre-alignment can reduce the cost of building common points by 26% while maintaining the coordinate conversion accuracy. In tunnel network measurement, accuracy can be increased by 28% using UWA. The methods proposed offer broad applicability in the field of particle accelerator alignment and guiding alignment solutions for HALF.

Syntheses, structures, and magnetic properties of new [Co9] cluster

A new spin-cluster compound K6BaCo9(PO4H)3(PO4)6Cl2 was synthesized by the traditional solid-phase method. The fundamental magnetic unit of the compound is a coupled [Co9] cluster, which is composed of three non-coplanar triangles. These [Co9] clusters are interconnected by phosphate groups, constructing a two-dimensional framework in the ab plane. The crystal shows the clear easy-axis anisotropy. No long-range magnetic ordering was observed down to 2 K, but there is short-range spin correlation below T = 2.45 K. The Curie-Weiss temperature is about θCW = −19.38 K for the powder sample, which indicates that the dominant exchange interaction is antiferromagnetic with strong frustration (f = |θCW|/T ≈ 10). The magnetization curve presents a likely magnetic field induced transition at μ0Hc = 1.85 T.

Wideband radar cross-section reduction by a double-layer-plasma-based metasurface

Reduction of the radar cross-section (RCS) is the key to stealth technology. To improve the RCS reduction effect of the designed checkerboard metasurface and overcome the limitation of thin-layer plasma in RCS reduction technology, a double-layer-plasma-based metasurface—composed of a checkerboard metasurface, a double-layer plasma and an air gap between them—was investigated. Based on the principle of backscattering cancellation, we designed a checkerboard metasurface composed of different artificial magnetic conductor units; the checkerboard metasurface can reflect vertically incident electromagnetic (EM) waves in four different inclined directions to reduce the RCS. Full-wave simulations confirm that the double-layer-plasma-based metasurface can improve the RCS reduction effect of the metasurface and the plasma. This is because in a band lower than the working band of the metasurface, the RCS reduction effect is mainly improved by the plasma layer. In the working band of the metasurface, impedance mismatching between the air gap and first plasma layer and between first and second plasma layers cause the scattered waves to become more dispersed, so the propagation path of the EM waves in the plasma becomes longer, increasing the absorption of the EM waves by the plasma. Thus, the RCS reduction effect is enhanced. The double-layer-plasma-based metasurface can be insensitive to the polarization of the incoming EM waves, and can also maintain a satisfactory RCS reduction band when the incident waves are oblique.

Topological magnons in a non-coplanar magnetic order on the triangular lattice

The bond-dependent Kitaev interaction K is familiar in the effective spin model of transition metal compounds with octahedral ligands. In this work, we find a peculiar non-coplanar magnetic order can be formed with the help of K and next-nearest neighbor Heisenberg coupling J 2 on the triangular lattice. It can be seen as a miniature version of skyrmion crystal, since it has nine spins and an integer topological number in a magnetic unit cell. The magnon excitations in such an order are studied by the linear spin-wave theory. Of note is that the change in the relative size of J 2 and K produces topological magnon phase transitions although the topological number remains unchanged. We also calculated the experimentally observable thermal Hall conductivity, and found that the signs of thermal Hall conductivity will change with topological phase transitions or temperature changes in certain regions.