Magnetic Excitations Research Articles

Coupled axial and transverse currents method for finite element modelling of periodic superconductors

In this paper, we propose the Coupled Axial and Transverse currents (I) (CATI) method, as an efficient and accurate finite element approach for modelling the electric and magnetic behavior of periodic composite superconducting conductors. The method consists of a pair of two-dimensional models coupled via circuit equations to account for the conductor geometrical periodicity. This allows to capture three-dimensional effects with two-dimensional models and leads to a significant reduction in computational time compared to conventional three-dimensional models. After presenting the method in detail, we verify it by comparison with reference finite element models, focussing on its application to twisted multifilamentary superconducting strands. In particular, we show that the CATI method captures the transition from uncoupled to coupled filaments, with accurate calculation of the interfilament coupling time constant. We then illustrate the capabilities of the method by generating detailed loss maps and magnetization curves of given strand types for a range of external transverse magnetic field excitations, with and without transport current.

Local Excitation of Kagome Spin Ice Magnetism Seen by Scanning Tunneling Microscopy.

The kagome spin ice can host frustrated magnetic excitations by flipping its local spin. Under an inelastic tunneling condition, the tip in a scanning tunneling microscope can flip the local spin, and we apply this technique to kagome metal HoAgGe with a long-range ordered spin ice ground state. Away from defects, we discover a pair of pronounced dips in the local tunneling spectrum at symmetrical bias voltages with negative intensity values, serving as a striking inelastic tunneling signal. This signal disappears above the spin ice formation temperature and has a dependence on the magnetic fields, demonstrating its intimate relation with the spin ice magnetism. We provide a two-level spin-flip model to explain the tunneling dips considering the spin ice magnetism under spin-orbit coupling. Our results uncover a local emergent excitation of spin ice magnetism in a kagome metal, suggesting that local electrical field induced spin flip climbs over a barrier caused by spin-orbital locking.

Bioinspired High-Linearity, Wide-Sensing-Range Flexible Stretchable Bioelectronics Based on MWCNTs/GR/Nd2Fe14B/PDMS Nanocomposites for Human-Computer Interaction and Biomechanics Detection.

In recent years, flexible and stretchable strain sensors have emerged as a prominent area of research, primarily due to their remarkable stretchability and extremely low strain detection threshold. Nevertheless, the advancement of sensors is currently constrained by issues such as complexity, high costs, and limited durability. To tackle the aforementioned issues, this study introduces a lepidophyte-inspired flexible, stretchable strain sensor (LIFSSS). The stretchable bioelectronics composites were composed of multiwalled carbon nanotubes, graphene, neodymium iron boron, and polydimethylsiloxane. Unique biolepidophyted microstructures and magnetic conductive nanocomposites interact with each other through synergistic interactions, resulting in the effective detection of tensile strain and magnetic excitation. The LIFSSS exhibits a 170% tensile range, a linearity of 0.99 in 50-170% strain (0.96 for full-scale range), and a fine durability of 7000 cycles at 110% tensile range. The sensor accurately detects variations in linear tensile force, human movement, and microexpressions. Moreover, LIFSSS demonstrates enhanced efficacy in sign language recognition for individuals with hearing impairments and magnetic grasping for robotic manipulators. Hence, the LIFSSS proposed in this study shows potential applications in various fields, including bioelectronics, electronic skin, and physiological activity monitoring.

Anapole states and transverse displacement sensing based on the interaction between cylindrical vector beams and Au core-Si shell nanodisks.

Precise optical control at the nanoscale is crucial for advancing photonic devices and sensing technologies. Herein, we theoretically introduce what we believe to be a novel approach for nano-optical manipulation, employing Au core-Si shell nanodisks interacting with tightly focused cylindrical vector beams to achieve electric and magnetic anapole states. Our investigations unveil that the interplay between individual nanodisks and radially polarized beams (RPBs) located in the center of RPBs yields a position-dependent electric anapole state. Conversely, under illumination by azimuthally polarized beams (APBs), the electric anapole state exhibits independence from the nanodisk's positioning and is accompanied by significant magnetic dipole excitations. Furthermore, the interaction between APBs and nanodisk multimers enables the formation of a magnetic anapole state, marking an advancement in nano-optical control. This study further explores the application of the position-dependent electric anapole state for nanoscale transverse displacement sensing, which allows for precise determination of the nanodisk's position within a plane. These findings not only facilitate versatile control over anapole states but also set a foundation for integrated displacement sensing technologies on-chip.

Experimental study on strengthening the magneto-mechanical coupling effect of X80 steel by weak magnetic excitation

Abstract Current magnetic stress detection techniques are significantly impacted by external noise signals. The magnetic stress detection technology under excitation magnetic fields is proposed to weaken the external noise signals on the detection results. In this study, the uniaxial tensile magnetic signal testing system with the excitation magnetic field was built. The enhancement of the weak magnetic excitation on magnetic signals has been quantitatively analyzed and the concept of optimal weak excitation magnetic field has been proposed. The response law between triaxial magnetic induction intensity and stress under the excitation magnetic field is determined. The results indicate that the weak excitation magnetic field significantly enhances the magnetic induction signal intensity, more importantly, the linearity of the magnetic signal and stress response is also enhanced. Furthermore, the optimal excitation magnetic field under uniaxial stress states is 600 A/m, and the corresponding stress-magnetic change rate is 0.002 Oe/MPa. This study provides a theoretical basis for the long-distance detection of pipelines under weak magnetic excitation. The long-distance magnetic stress detection results of pipelines will become more accurate with the weak magnetic excitation which has a good engineering significance.

Observation of the sliding phason mode of the incommensurate magnetic texture in Fe/Ir(111)

The nanoscopic magnetic texture forming in a monolayer of iron on the (111) surface of iridium, Fe/Ir(111), is spatially modulated and uniaxially incommensurate with respect to the crystallographic periodicities. As a consequence, a low-energy magnetic excitation is expected that corresponds to the sliding of the texture along the incommensurate direction, i.e., a phason mode, which we explicitly confirm with atomistic spin simulations. Using scanning tunneling microscopy (STM), we succeed to observe this phason mode experimentally. It can be excited by the STM tip, which leads to a random telegraph noise in the tunneling current that we attribute to the presence of two minima in the phason potential due to the presence of disorder in our sample. This provides the prospect of a floating phase in cleaner samples and, potentially, a commensurate-incommensurate transition as a function of external control parameters.

Numerical Simulation of Thermal Therapy for Melanoma in Mice.

In recent years, the progressively escalating incidence and exceptionally high fatality rate of cutaneous melanoma have drawn the attention of numerous scholars. Magnetic induction hyperthermia, as an efficacious tumor treatment modality, has been promoted and applied in the therapy of some tumors. In this paper, the melanoma atop the mice's heads was chosen as the research subject, and a magnetic induction hyperthermia approach based on Helmholtz coils as the magnetic field excitation was investigated and designed. The influence of the electromagnetic field and thermal field on organisms was addressed through modeling by COMSOL simulation software. The results showed that the maximum values of induced electric field and magnetic induction strength in mouse tumor tissues were 63.1 V/m and 8.5621 mT, respectively, which reached the threshold value of magnetic field strength required for magnetic induction hyperthermia. The maxima of the induced electric field and magnetic induction intensity in brain tissues are, respectively, 35.828 V/m and 8.57 mT. Approximately 93% of the tumor tissue can reach 42 °C, and the maximum temperature is 44.2 °C. Within this temperature range, a large quantity of tumor cells can be successfully induced to undergo apoptosis without harming normal cells, and the therapeutic effect is favorable.

Magnetic vortex polarity reversal induced gyrotropic motion spectrum splitting in a ferromagnetic disk

We investigate the gyrotropic motion of the magnetic vortex core in a chain of a few micron-sized Permalloy disks by electrical resistance measurement with amplitude-modulated magnetic field. We observe a distinctive splitting of the resistance peak due to the resonant vortex-core motion under heightened radio frequency (RF) magnetic field excitation. Our micromagnetic simulation identifies the splitting of the resonant peak as an outcome of vortex polarity reversal under substantial RF amplitudes. This study enhances our understanding of nonlinear magnetic vortex dynamics amidst large RF amplitudes and proposes a potential pathway for spintronic neural computing thanks to their unique and controllable magnetization dynamics.

Key influence factors in magneto-controlled motion of micro-nano graphite flakes

Magneto-controlling micro-nano materials’ motion is a promising way that enable the noncontact, remote, and nondestructive controlling of their macrostructure as well as functionalities. Here, an optical microscope with an electromagnet was constructed to in-situ monitor the magneto-controlled motion process microscopically. Taking micro-nano graphite flake (MGF) as a model system, we experimentally demonstrate the key factors that influence the magneto-controlling of materials’ motion. First, the product of intensity and gradient of the magnetic field (B∇B) has been confirmed as the dominant driving force and the flipping direction of the MGFs is accordingly determined by the vector direction of B×∇B. Second, quantitatively comparative experiments further revealed that the threshold driving force has an exponential relationship with the structural aspect ratio (b/a) of MGFs. Third, the critical magneto-driving force is found as proportional to the viscosity of the solvent. Accordingly, a dynamic model is developed that describes the flip of the diamagnetic flake under external magnetic field excitation considering the shape factor. It is shown experimentally that the model accurately predicts the flip dynamics of the flake under different magnetic field conditions. In addition, we also discovered the delay effect, multiple cycle acceleration effect, and the fatigue effects due to gas adsorption in magneto-controlled MGFs flipping. These findings can be used to achieve magneto-controlling materials’ macrostructure as well as their functionalities.

Magnetic excitations in strained infinite-layer nickelate PrNiO2 films

Strongly correlated materials respond sensitively to external perturbations such as strain, pressure, and doping. In the recently discovered superconducting infinite-layer nickelates, the superconducting transition temperature can be enhanced via only ~ 1% compressive strain-tuning with the root of such enhancement still being elusive. Using resonant inelastic x-ray scattering (RIXS), we investigate the magnetic excitations in infinite-layer PrNiO2 thin films grown on two different substrates, namely SrTiO3 (STO) and (LaAlO3)0.3(Sr2TaAlO6)0.7 (LSAT) enforcing different strain on the nickelates films. The magnon bandwidth of PrNiO2 shows only marginal response to strain-tuning, in sharp contrast to the enhancement of the superconducting transition temperature Tc in the doped superconducting samples. These results suggest the bandwidth of spin excitations of the parent compounds is similar under strain while Tc in the doped ones is not, and thus provide important empirics for the understanding of superconductivity in infinite-layer nickelates.

DECREASING TORQUE RIPPLE OF A SLOTLESS PERMANENT MAGNET TORQUE MOTOR USING A DOUBLE-LAYER WINDING

The torque of a magnetoelectric torque motor with surface-mounted permanent magnets on the rotor was studied. The sinusoidal current supply mode is considered. The torque was calculated according to the static model of the magnetic field. It was determined that the sixth harmonic makes a significant contribution to the torque ripple. To reduce the sixth harmonic it is proposed to use a winding with a shortened pitch, for which it is necessary to make this winding in two layers. The optimal values of the number of pole pairs, the angular width of the magnets of the magnetic field exci-tation system, and the shortening of the winding pitch were determined. It was found that shortening of the winding pitch decreases the torque ripple by 2 ... 2.5 times. References 7, figures 6, tables 3.

Infrared radiation absorption in a wide wavelength range of 3–14 μm mainly based on spatial magnetic plasmon excitation and accumulation in an arrayed nanocavity-shaped metasurface

Infrared radiation absorption in a wide wavelength range of 3–14 <i>μ</i>m mainly based on spatial magnetic plasmon excitation and accumulation in an arrayed nanocavity-shaped metasurface

The impacts of spin–orbit coupling and strain on transverse dynamical spin susceptibility in undoped phosphorene: Kane–Mele model study

We present the behaviors of dynamical transverse spin susceptibilities of undoped phosphorene monolayer using the Green’s function approach in the context of Kane–Mele model Hamiltonian. Such dynamical spin susceptibility is proportional to inelastic cross section of neutron beam from the layer. Specially, the effects of magnetic field and spin–orbit coupling strength on the spin excitation modes of phosphorene monolayer are investigated via calculating correlation function of spin density operators. Our results show the increase of magnetic field leads to move the magnetic excitation energy to higher values. Also, the intensity of peaks in inelastic cross section reduces with increase of magnetic field. We also show that applying both uniaxial and biaxial strains causes to decrease the intensity of peaks in dynamical spin susceptibility. Finally the effects of both compressive and tensile strains on frequency dependence of dynamical spin structure factor of phosphorene layer are studied. Moreover, the frequency positions of spin excitation mode of phosphorene layer have been investigated due to the effects of spin orbit coupling strength in details.

Electron–ion collision and polarization of X-ray fluorescence radiation under hot quantum plasma conditions

In the current article, the spectral properties and electron collision (total and magnetic) excitation cross sections of ions taking placed in quantum plasmas are investigated. These cross sections are further used to study the polarization and angular distribution characteristics of the de-excitation radiation X-ray spectra, which play an important role in basic theoretical research, the diagnosis of the plasma environment, and the design of optical devices. To do so, a distorted wave method within the relativistic Dirac–Coulomb atomic structure scheme is suggested. The effective interaction potential between electrons and particles in hot quantum plasmas in the method is determined using a quantum approach that incorporates the influence of effective plasma screening effects caused by collective plasma oscillations. This potential replaces the traditional Coulomb interaction potential and is used in solving the modified Dirac equation to obtain the bound and continuum electron wave functions. Higher-order relativistic effects, such as the Breit interaction and the dominant quantum electrodynamics corrections, are added to enhance the accuracy of the method. Detailed calculations for the relativistic atomic structure and collision excitation dynamics process are carried out, taking the highly stripped H-like O7+ ion of astrophysical importance as an illustrative example. Detailed investigations are also conducted on the variation of energies, collision cross sections, and fluorescence polarizations as functions of the plasma parameters. Our results suggest that the joint effects of shielding and plasma coupling lead the energies, cross sections and fluorescence polarizations decrease (compared with the isolated case). The angular distribution of the X-ray fluorescence emission shows large change, suggesting their sensitivity to these effects. This study not only offers a valuable approach to investigating the plasma shielding and plasmon coupling effects in quantum plasmas but also holds significant relevance for applications in controlled nuclear fusion, astrophysical plasmas and so on.

Analytical model of magnetic Barkhausen noise testing on surface-modified ferromagnetic plates with stress distributions

Surface treatment is a critical technology in engineering that enhances the mechanical properties of materials, in which the stress state within the material and the thickness of the surface modification layer are essential for optimizing performance. Magnetic Barkhausen Noise (MBN) serves as an effective nondestructive evaluation technique for ferromagnetic structures. In this work, we develop an analytical model that incorporates the attenuation mechanism of the MBN signal strength, and the strength of the stress-induced magnetic Barkhausen excitation (MBE) as determined by the magneto-mechanical constitutive law of the material. The proposed theoretical model can accurately characterize the MBN signal influenced by internal stresses and surface modification layers, as confirmed by comparison with existing experimental results. The theoretical analysis shows the influence of internal stress fields, layer dimensions, and electromagnetic properties on the MBN signal, revealing a positive relationship between signal intensity and the thickness of surface modification layer and the magnitude of internal stresses. This research provides a valuable reference for interpreting MBN signals and evaluating internal stress distributions for surface-modified ferromagnetic plates.

Research on Torque Performance of Marine Hybrid Excitation Synchronous Motors Based on PSO Optimization of Magnetic Permeability Structure

The rotor magnetic shunt structure hybrid excitation synchronous motor (RMS-HESM) has been widely used in marine propulsion due to its advantages of low loss and high efficiency. The objective of this paper is to improve the output torque capability of the hybrid excitation motor with a rotor magnetic shunt structure by conducting a multi-objective optimization design for the magnetic permeability structure. The first step involved establishing a mathematical analytical model of average torque and torque ripple based on the fundamental principle of motor magnetization. Next, the parameters of the magnetic permeability structure were designed and analyzed using the finite element simulation method. The impact of the variations in the parameters of the magnetic permeability structure on motor torque and no−load back electromotive force was examined. Additionally, a sensitivity analysis was performed on the design variables of the magnetic permeability structure, leading to the determination of optimization parameters based on the obtained results. The adaptive inertia weight-based particle swarm algorithm (PSO) was employed to conduct a multi-objective optimization design analysis. A comparative analysis on the average torque, torque ripple, and no−load back electromotive force of the motor before and after optimization was performed using the Maxwell and Workbench and Optislong joint simulation tools. This enhancement significantly improves the torque performance of the marine motor while simultaneously optimizing the no−load back electromotive force.

Powering piezoelectric frequency up-converter with rotary magnetic forces for torque-sensing application

A piezoelectric frequency up-energy harvester (PFU-EH) utilizing an SECE circuit (synchronized electric charge extraction) is developed for torque-sensing application in rotating machinery. Development of an explicit theoretical model for the system with the PFU-EH, considering phase angle shifts and magnetic impulsive forces is proposed to formulate the frequency response equations for voltage and power outputs using Fourier analysis. In this study, harvesting electrical energy can be achieved through the magnetic force interaction between the cantilevered piezoelectric beam, which carries two attached magnets, and the compound rotating disk structure, also carrying two attached magnets. The compound rotating disk structure, composed of a metal ring (outer disk) and a flywheel (inner disk) connected by a spring system, can create a phase angle caused by an applied load. As a result, mechanical torque is formed for inducing magnetic excitation to the PFU-EH and subsequently generating an AC voltage signal. The functionality of the AC voltage harvested by the PFU-EH can be further leveraged for two primary benefits. First, it can be converted into DC voltage output using the SECE circuit, enhancing the effectiveness of the electric signal without requiring load matching under different modal vibrations. Second, the SECE harvesting voltage can simultaneously function as a sensing signal for detecting mechanical torque itself. The sensing signal detection process is further analyzed by applying feature extraction from the spectrogram and utilizing a 2D-CNN for auxiliary segment identification. Finally, the experimental results demonstrate reasonable agreement with the predicted outcomes.

Dynamic modeling and analysis of viscoelastic hard-magnetic soft actuators with thermal effects

Hard-magnetic soft materials (HMSMs) are a class of magnetoactive smart polymers capable of sustaining a high residual magnetic flux density and can undergo large actuation strains under an external magnetic excitation. Due to these exceptional characteristics, soft actuators based on HMSMs hold enormous potential for remote-controlled applications. The temperature and viscoelasticity considerably influence the performance of these materials during the operation. This work aims to develop an analytical framework for modeling the dynamic behavior of a planar hard-magnetic soft actuators (HMSA) considering temperature and viscoelastic effects. The constitutive behavior of the viscoelastic HMSA is described by employing an incompressible neo-Hookean model in conjunction with a Zener rheological model and the Rayleigh dissipation function. The dynamic governing differential equations of motion are derived by utilizing the non-conservative form of the Euler–Lagrange equation. This study delves into the collective influence of temperature and viscoelastic properties on the stability, periodicity, and resonance characteristics of nonlinear vibrations exhibited by HMSM-based planar actuator subjected to dynamic magnetic loading, presenting the findings through time-history responses, Poincaré maps, and phase-plane plots. The presented results can help in the efficient and robust design of HMSM-based actuators and can also serve as an initial step toward the development of advanced actuators exposed to dynamic loading under variable temperatures for diverse applications in the fields of engineering and medicine.

Remotely Controlled Surface Charge Modulation of Magnetoelectric Nanogenerators for Swift and Efficient Drug Delivery.

We have developed a highly efficient technique of magnetically controlled swift loading and release of doxorubicin (DOX) drug using a magnetoelectric nanogenerator (MENG). Core-shell nanostructured MENG with a magnetostrictive core and piezoelectric shell act as field-responsive nanocarriers and possess the capability of field-triggered drug release in a cancerous environment. MENGs generate a surface electric dipole when subjected to a magnetic field due to the strain-mediated magnetoelectric effect. The capability of directional magnetic field-assisted modulation of the surface electrical dipole of MENG provides a mechanism to create/break ionic bonds with DOX molecules, which facilitates efficient drug attachment and on-demand swift detachment of the drug at a targeted site. The magnetic field-assisted drug-loading mechanism was minutely analyzed using spectrophotometry and Raman spectroscopy. The detailed time-dependent analysis of controlled drug release by the MENG under unidirectional and rotating magnetic field excitation was conducted using field-emission scanning electron microscopy, energy-dispersive X-ray, and atomic force microscopic measurements. In vitro, experiments validate the cytocompatibility and magnetically assisted on-demand and swift DOX drug delivery by the MENG near MCF-7 breast cancer cells, which results in a significant enhancement of cancer cell killing efficiency. A state-of-the-art experiment was performed to visualize the nanoscale magnetoelectric effect of MENG using off-axis electron holography under Lorentz conditions.

Antiferromagnetism in two-dimensional materials: progress and computational challenges

We present a perspective on the status of antiferromagnetism in two-dimensional (2D) materials. Various types of spin-compensated orders are discussed and include non-collinear order, spin spirals and altermagnetism. Spin–orbit effects ultimately determine, whether compounds exhibit long range order, Kosterlitz-Thouless physics, or multiferroic properties and we discuss the basic magnetic prototypes that may arise in 2D materials depending on the magnetic anisotropy and ordering vector. A summary of 2D antiferromagnets that have been characterized experimentally is provided—with particular emphasis on magnetic anisotropies and Neel temperatures. We then outline the ingredients needed to describe the magnetic properties using density functional theory. In particular, the systematic determination of magnetic ground states from the generalized Bloch theorem and the magnetic force theorem, which may be used to calculate magnetic excitations from the Heisenberg model with parameters determined from first principles. The methods are exemplified by application to the monolayer helimagnet NiBr2. Finally, we present a summary of predicted and prospective 2D antiferromagnets and discuss the challenges associated with the prediction of Néel temperatures from first principles.