Magnetic Field Research Articles

Landau levels induced by synthetic strain in plasmonic metasurface

The quantum Hall effect arises when electrons in a two-dimensional plane are subjected to a magnetic field, causing them to undergo cyclotron motion and form discrete energy levels, known as Landau levels. These levels play a critical role in condensed matter physics. However, practical limitations of applying a magnetic field have led to the introduction of pseudomagnetic fields, which can similarly induce Landau levels. Such pseudomagnetic fields are typically generated through synthetic strain, achieved by deforming geometric patterns, and have been applied to systems like graphene, photons, and phonon crystals. Building on previous research in electronics and optics, we present a plasmonic metasurface that induces Landau levels via synthetic strain in the microwave frequency range. This strain is realized by printing metal structures of specific shapes on a dielectric substrate using printed circuit board technology. The fundamental unit of the plasmonic metasurface is a C6 symmetric structure composed of six localized surface plasmon patches. By applying a displacement function along the transmission direction, we discretize the dispersion curve, leading to band degeneration and the emergence of edge states. The distribution of these edge states is influenced by the strength of the pseudomagnetic field, which is controlled by the magnitude of the displacement function. We validate our design through fabricated models and demonstrate the existence of edge states using near-field scanning experiments. Our work, which combines synthetic magnetic fields and plasmonic metasurface, provides valuable insights for the development and application of integrated photonic devices.

High‐Load Shape Memory Microgripper with Embedded Resistive Heating and Magnetic Actuation

AbstractMagnetically actuated soft grippers find extensive applications in robotics due to their rapid response, biological safety, and wireless control capabilities. However, these systems often require a continuously applied magnetic field during both the capture and release processes, which reduces load capacity and makes gripping ferromagnetic objects challenging. Here, an electrothermal‐magnetic actuated shape memory (EM‐SMP) microgripper is developed. By incorporating Fe₃O₄ particles into the shape memory polymer (SMP) and embedding resistive wires, the microgripper can respond to both electric current and magnetic field. The high thermal conductivity of the composite material, coupled with microscale dimensions achieved via femtosecond laser processing, significantly enhances the response speed (≈0.9 s). The magnetic field is applied only to open the gripper, while closure is realized through the electrothermal‐triggered shape memory effect, allowing sequential closure to safely grip delicate soft objects and magnetic objects without magnetic interference. Upon cooling, the closed state of the SMP gripper locks in place without energy consumption. Furthermore, the claw‐shaped design allows the gripper to enclose larger objects during grasping, thereby improving the load‐to‐weight ratio (≈2380). This gripper demonstrates broad application potential, effectively performing grasp and release tasks across diverse materials, sizes, shapes, states, and extreme environmental conditions (acidic and alkaline).

Unsteady MHD Free Convective Flow of a Micro‐Polar Fluids Over a Vertical Porous Plate in the Presence of Radiation and Chemical Reaction

ABSTRACTObjective of the paper is to investigate the motion of an unsteady free convective MHD flow of a micro‐polar fluid over semi‐infinite vertically moving porous plate in the presence of chemical reaction and thermal radiation. A transverse magnetic field is applied, assuming a low magnetic Reynolds number. We have discussed the effects of heat radiation due to a heat source and first order chemical reaction within the medium. The perturbation method is applied to solve the nonlinear coupled partial differential equations in their dimensionless form, converting them into a system of ordinary differential equations, which are then solved analytically. The effects of magnetic field, medium permeability, buoyancy force, heat source, concentration gradient, Prandtl number, thermal diffusion, heat radiation, and first order chemical reaction on velocity, temperature and concentration are discussed graphically. The graphical representations are generated using MATLAB software. For engineering interest, their effects on skin friction, heat and mass transfer in terms of Nusselt number and Sherwood number are discussed; numerical values are shown in tabular form. The results show that magnetic fields reduce fluid velocity, while thermal radiation decreases temperature, and chemical reactions lower concentration. Radiation increases skin friction and heat transfer, while chemical reactions reduce mass transfer. Findings have relevance in various problems and situations arising with micro‐polar fluidic devices, industrial like petroleum and lubrication, mixing etc.

Thermal Variability in the Martian Upper Atmosphere within the Crustal Magnetic Field Region Induced by Gravity Wave Dissipation Due to Ion-drag Effect

Abstract Mars Atmosphere and Volatile Evolution detected a significant temperature increase of approximately 20–40 K in the upper atmosphere within the strong crustal magnetic field (CF) region during two deep dip campaigns. Previous studies were unable to fully explain this thermal variation. Atmospheric gravity waves are an underlying mechanism, attributed to the ion-drag effect. During this effect process, the collisions between neutral particles and ions transfer wave momentum along the magnetic field lines, and lead to wave dissipation and energy release to heat or cool the background atmosphere. We developed a one-dimensional linear wave model to describe the effect of ion-drag on wave propagation and dissipation in the Martian upper atmosphere. Our results show that the ion-drag effect influences wave propagation primarily above 160 km in the CF region and around 200 km in the noncrustal magnetic field (NCF) region. The total wave energy flux driven by the ion-drag effect in the CF region is approximately 108 eV cm−2 s−1, with heating rates of 10–60 K per sol and cooling rates up to 40 K per sol above 155 km. Wave-driven temperature enhancements in the CF region due to the ion-drag effect are a few Kelvins higher than in the NCF regions, though still smaller than the observed 20–40 K. Additional wave processes, including wave breaking and multiwave dissipation, may contribute to the observed thermal variability and should be considered in future studies.

Refractive index and magnetic field sensing based on bent microfiber functionalized with graphene oxide

A bent tapered multimode fiber structure for refractive index (RI) and magnetic field sensing applications is proposed and investigated. The bent tapered region deposited with gold film to excite surface plasmon resonance (SPR) functions as the sensing area. Further surface functionalization with graphene oxide (GO) enhances the SPR effect. The high sensitivity of 5260.1 nm/RIU in the RI range of 1.33–1.37 is achieved. Magnetic fluid is used as the magneto-sensitive material, and the achieved magnetic field intensity and directional sensitivities are 7.08 nm/mT and 0.15 nm/°, respectively. The surface functionalization of GO extends the magnetic field sensor's detection range up to 30 mT. The proposed sensor features a simple structure, low cost, point-sensing capability, and excellent mechanical properties, making it highly suitable for various practical applications.

Nanosatellite Autonomous Navigation via Extreme Learning Machine Using Magnetometer Measurements

This work presents an algorithm to perform autonomous navigation in spacecraft using onboard magnetometer data during GPS outages. An Extended Kalman Filter (EKF) exploiting magnetic field measurements is combined with a Single-Hidden-Layer Feedforward Neural Network (SLFN) trained via the Extreme Learning Machine to improve the accuracy of the state estimate. The SLFN is trained using GPS data when available and predicts the state correction to be applied to the EKF estimates. The CHAOS-7 magnetic field model is used to generate the magnetometer measurements, while a 13th-order IGRF model is exploited by the EKF. Tests on simulated data showed that the algorithm improved the state estimate provided by the EKF by a factor of 2.4 for a total of 51 days when trained on 5 days of GPS data.

Tuning the interfacial transport behavior in a superconducting van der Waals heterostructure

The interaction between the metallic and superconducting components at the interface of superconductor–normal metal (S-N) systems enables a variety of quantum phenomena, including the Josephson effect, Andreev reflection, and proximity-induced superconductivity, which are of significant interest both theoretically and practically. Nevertheless, due to varying physical mechanisms, achieving and fine-tuning multiple such phenomena within a single S-N system continues to be a challenge. In this work, we employ NbSe2 and WTe2 to fabricate an S-N-S heterostructure. Below the superconducting transition temperature of NbSe2, two distinct resistance-temperature behaviors are observed: a continuous decrease in junction resistance with temperature decrease, indicative of the superconducting proximity effect and consistent with the BCS model, and an increase in resistance attributed to competition between Andreev reflection (AR) and normal reflection at a low-transparency interface, which can be suppressed by applying a small bias current or a magnetic field. Our results indicate the signature of the coexistence of proximity-induced superconductivity with AR in the measured S-N-S heterojunction, demonstrating the tunability of charge carrier transport behavior at the interface. This finding enhances our understanding of such systems and holds potential for the development of superconducting electronics, quantum computing, and energy harvesting technologies.

Ultrafast emergence of ferromagnetism in antiferromagnetic FeRh in high magnetic fields

Ultrafast heating of FeRh by a femtosecond laser pulse launches a magneto-structural phase transition from an antiferromagnetic to a ferromagnetic state. Aiming to reveal the ultrafast kinetics of this transition, we studied magnetization dynamics with the help of the magneto-optical Kerr effect in a broad range of temperatures (from 4 K to 400 K) and magnetic fields (up to 25 T). Three different types of ultrafast magnetization dynamics were observed and, using a numerically calculated H-T phase diagram, the differences were explained by different initial states of FeRh corresponding to a (i) collinear antiferromagnetic, (ii) canted antiferromagnetic and (iii) ferromagnetic alignment of spins. We argue that ultrafast heating of FeRh in the canted antiferromagnetic phase launches practically the fastest possible emergence of ferromagnetism in this material. The magnetization emerges on a time scale of 2 ps, which corresponds to the earlier reported time scale of the structural changes during the phase transition.

ULtimate MAGnetic characterization (ULMAG) at the ID12 beamline of ESRF: from element-specific properties to macroscopic functionalities

We present a novel instrument designed for advanced magnetic study, installed at the ID12 beamline of the European Synchrotron Radiation Facility in Grenoble, France. This instrument offers the unique capability to simultaneously measure element-specific microscopic and macroscopic properties related to the magnetic, electronic and structural characteristics of materials. In addition to X-ray absorption, X-ray magnetic circular dichroism alongside X-ray diffraction patterns, the macroscopic magnetization, volume changes, caloric properties and electrical resistivity of magnetic materials could be measured strictly under the same experimental conditions as a function of both magnetic field (up to ±7 T) and temperature (ranging from 2.05 K to 325 K). To demonstrate the capability of this new instrument, we present two case studies highlighting its performance in investigating first-order magneto-structural phase transitions, namely in DyCo2 and FeRh alloys.

Electromagnetic non-orthognal flow of variable viscosity nanofluid over a rotating riga disk with prescribed thermal slip

Abstract This paper investigates the complex dynamics of a 3D oblique magneto hydrodynamic (MHD) flow of Ag-water Nanofluid across a rotating Riga disk. Temperature dependent viscosity along with prescribed momentum and thermal slip on the surface of rotating Riga disk are taken into account. Permanent magnets are attached to a flat surface of the electrode array on Riga plate, which is oriented span-wise. This configuration produces an exponentially decaying Lorentz force parallel to the array. The interaction of magnetic fields, rotational effects, and boundary slip phenomena in a three-dimensional flow is the main topic of the study. The study uses the Shooting algorithm to investigate the effects of the Riga disk's rotation and the presence of a magnetic field on heat transfer and flow characteristics. Furthermore, the addition of momentum and thermal slip boundary conditions sheds more light on differences between realistic situations and standard no-slip models. With implications for better design and optimization in engineering systems involving rotating disks and magnetic fields, this work advances our understanding of complex fluid dynamics in MHD applications. Velocity profiles f ′ ( η ) and g(η) drops down while enhancing values of nano particle volume fraction ϕ whereas g(η) reduces by ehancement of Hartman number Ha and velocity slip parameter ω 1. The temperature θ(η) rises with increasing thermal slip ω 2 velocity slip parameter ω 1 and Hartmann number Ha. Additionally, it increases with the volume fraction of solid nanoparticles ϕ and the width parameter δ. As width parameter δ increases, the local heat flux − K n f K f . θ ′ ( 0 ) decreases. Skin friction coefficient f″(0) increases with viscosity parameter m and decreases with variations in thermal slip parameter ω 2. 3D flow patterns exhibits the significant influence of momentum slip parameter ω 1 on the location of stagnation point.

Tunneling photo-thermoelectric effect in monolayer graphene/bilayer hexagonal boron nitride/bilayer graphene asymmetric van der Waals tunnel junctions

Graphene exhibits a pronounced photo-thermoelectric effect (PTE) in its in-plane carrier transport and has attracted attention toward various optoelectronic applications. In this study, we demonstrate an out-of-plane PTE by utilizing electron tunneling across a barrier, namely, the tunneling photo-thermoelectric effect (TPTE). This was achieved in a monolayer graphene (MLG)/bilayer hexagonal boron nitride (h-BN)/bilayer graphene (BLG) asymmetric tunnel junction. MLG and BLG exhibit different cyclotron resonance (CR) optical absorption energies when their energies are Landau quantized under an out-of-plane magnetic field. We tuned the magnetic field under mid-infrared irradiation to bring MLG into CR conditions, whereas BLG was not in CR. The CR absorption in the MLG generates an electron temperature difference between the MLG and BLG and induces an out-of-plane TPTE voltage across the h-BN tunnel barrier. The TPTE exhibited a unique dependence on the Fermi energy of the MLG, which differed from that of the in-plane PTE of the MLG. The TPTE signal was large when the Fermi energy of the MLG was tuned near the transition between the quantum Hall state (QHS) and non-QHS. The TPTE allows one to measure the PTE on vertically stacked tunnel junctions, thus providing another degree of freedom for probing the electronic and optoelectronic properties of two-dimensional material heterostructures.

Snapping Endows Magnetoelectric Metamaterials with Passive Power-up Conversion.

Harnessing slowly varying or quasi-static magnetic fields, which typically lack the power to light an LED, to power devices with higher demands seems to be impossible if no additional power is supplied. Obviously, the key to overcoming this challenge is to achieve passive power conversion from low-power inputs into high-power outputs. Here, we propose that snap-through buckling─a mechanical instability phenomenon─within a magnetoelectric metamaterial enables passive power-up conversion. Our experimental results indicate that the instantaneous pulsed output power at snapping remains stable even as the frequency decreases by 100 times and exceeds the maximum magnetic input power by 27 times at a low working frequency of 0.01 Hz. Furthermore, for an array of magnetoelectric metamaterials with varying critical magnetic fields, we demonstrate that a series of pulsed outputs can result in continuous electrical output. We anticipate that these findings will open new avenues for advanced energy conversion technologies, underscoring a pioneering application of mechanical principles in materials science.

Energy Distribution Effect on Bremsstrahlung Radiation Produced by \(B_{11}^{5}\) and \(Al_{27}^{13}\)

By using the Bethe-Heitler equation, this work determines the energy distribution of Bremsstrahlung radiation for \(B_{11}^{5}\) and \(Al_{27}^{13}\). We utilize the mathematical program "Mathematica" to contrast the electromagnetic impacts of photons resulting from interactions of electrons with boron and aluminum nuclei. We compare the effects of electric and magnetic cross-sections on the generation of Bremsstrahlung radiation. We will examine the impact of electric and magnetic fields on the production of Bremsstrahlung radiation using graphs. We also investigate the effect of atom mass on the emission of Bremsstrahlung radiation. According to our results, certain types of X-rays can be produced by using magnetic interactions.

The Magnetic Origin of the Mystery of Rare Hα Moreton Waves

Abstract Over the past three decades, a lot of coronal fast-mode waves have been detected by space missions, but their counterparts in the chromosphere, called Moreton waves, have rarely been captured. How this happens remains a mystery. Here, to shed light on this problem, we investigate the photospheric vector magnetograms of the Moreton-wave events associated with M- and X-class solar flares during 2010–2023. The Hα data are taken with the Global Oscillation Network Group and the Chinese Hα Solar Explorer. Our statistical results show that more than 80% of the events occur at the edges of active regions and propagate nonradially, due to asymmetric magnetic fields above the flares. According to the reconstructed magnetic field and atmospheric model, Moreton waves propagate in the direction along which the horizontal fast-mode wave speed drops the fastest. This result supports the inclined magnetic configuration of the eruption being crucial for generating Moreton waves, even for X-class flares. It may explain the low occurrence rate of Moreton waves and why some X-class flares accompanied with coronal mass ejections do not generate Moreton waves.

Multimodal Splitting and Reciprocating Transport of Droplets on a Reprogrammable Functional Surface.

Droplet manipulations have important applications in many fields, especially droplet splitting and transport in aseptic operations or biochemical reagent analysis. However, droplet splitting or transport on existing functional surfaces is limited to predesigned microstructures or fixed patterns. It remains a challenge to realize reprogrammable surface microstructures for freely controllable droplet splitting and transport. In this study, a flexible technique for both the multimodal splitting and reciprocating transport of droplets on one surface is proposed. Such a surface is prepared with a facile fabrication method by premixing magnetic particles and softener into the polymer solvent matrix and immersing the solidified matrix in a lubricant. The movable wettability gradient is generated on the surface by an external magnetic field, which can act as an invisible "air knife" to split the droplet in multiple modes. The mechanism and critical conditions of droplet splitting are analyzed and revealed theoretically. Furthermore, the microstructural configurations and surface wettability can be reprogrammed by modulating the magnetic field strength and gradient. Accordingly, the splitting behavior of the droplet is transformed into the reciprocating transport behavior. The influencing factors of such behavior have also been analyzed. The reported reprogrammable manipulation of the droplet on one surface provides a versatile prototype for the actuation of droplets in microfluidic and biological analysis devices.

Charged particles in dipole magnetosphere of neutron stars: epicyclic oscillations in and off-equatorial plane

Abstract We study the motion of charged test particles around a magnetized neutron star described by the Schwarzschild gravitational field of mass M and a dipole magnetic field characterized by parameter b, representing the ratio of electromagnetic to gravitational forces. The neutron star’s radius is assumed at $$R=3M$$ R = 3 M . Circular orbits “in” and “off” the equatorial plane, determined by the dipole field’s symmetry plane, are analyzed based on background and particle parameters; their stability against radial and latitudinal perturbations is established. The existence of chaotic charged particle motion in belts around off-equatorial orbits, influenced by sufficiently strong repulsive magnetic force, is demonstrated. The belts’ distance from the neutron star varies with parameter b for different charged particles. Frequencies of epicyclic oscillatory motion related to “in” and “off” equatorial circular orbits, alongside the orbital frequency, are determined. The magnetically modified geodesic model is applied to fit observational data from twin-peak, high-frequency quasi-periodic oscillations in binary systems containing neutron stars. Rough fitting to the data for circular orbits for particles under magnetic attraction (repulsion) is shown. The possible fittings imply strong limits on the magnetic parameter, $$b \sim 0.01$$ b ∼ 0.01 ( $$b \sim -10$$ b ∼ - 10 ) for magnetic attraction (repulsion), suggesting minor influence of electromagnetic forces and test particles with small specific charges like dust or plasmoids in strong magnetic fields around neutron stars.

Discretizing the bistability of mode-locked electron spin precession: An Overhauser field hysteresis manifestation

Electron-nuclear spin interactions by pulsed optical pumping have been found to polarize the nuclear spin system, leading to the nuclei building up an intrinsic magnetic field known as the Overhauser field. Studies have indicated an Overhauser field hysteresis effect dependent on the sweep direction of an externally applied magnetic field in negatively detuned periodically pumped Si-doped GaAs. Although predictions of bistable mode-locked electron spin precession frequency modes have been made for systems exhibiting this hysteresis, there have been no reports on the experimental observation of said bistable spin precession modes. This report details the evolution of bistable Overhauser field solutions leading to a hysteretic effect in negatively detuned optical excitation of Si-doped GaAs by magneto-optic pump–probe spectroscopy in the Voigt geometry and investigates the resulting consequence of this hysteresis acting on the electron spin system. One manifestation of the Overhauser field hysteresis acting on the electron spin system leads to the discretization of bistable mode-locked electron spin precession modes within a given band of externally applied magnetic fields. A method for preferentially accessing the two different and stable mode-locked spin precession modes within a given band of externally applied magnetic field is outlined, which may be of interest for communities utilizing electron and nuclear spins for information processing protocols.

Room-Temperature Organic Spintronic Devices with Wide Range Magnetocurrent Tuning and Multifunctionality via Electro-Optical Compensation Strategy.

In spintronics, devices exhibiting large, widely tunable magnetocurrent (MC) values at room temperature are particularly appealing due to their potential in advanced sensing, data storage, and multifunctional technologies. Organic semiconductors (OSCs), with their rich and unique spin-dependent and (opto-)electronic properties, hold significant promise for realizing such devices. However, current organic devices are constrained by limited design strategies, yielding MC values typically confined to tens of percent, thereby restricting their potential for multifunctional applications. Here, this study introduces an electro-optical compensation strategy to modulate MC values, which synergistically integrates and manages the interplays among carrier transport, spin-dependent reactions, and photogenerated carrier dynamics in OSCs-based devices. This approach achieves ultrahigh room-temperature MC values of +13200% and -10600% in the designed devices, with continuous and precise tunability over this range-marking a breakthrough in organic spintronic devices. Building on this achievement, by integrating multiple controllable parameters-light, bias, magnetic field, and mechanical flexibility-into a single device, a flexible, room-temperature, multifunctional device is activated, functioning as the high-sensitivity magnetic field sensor, composite field sensor, magnetic current inverter, and magnetically-controlled artificial synaptic, etc. These findings open an avenue for designing high-performance, multifunctional devices with broad implications for future spintronic-related technologies.

Лазерно-ультразвуковое когнитивное преобразование энергии и информации в электроприводе

Energy-efficiency in contemporary electromachine technology depend on characteristics electrodrives, that requires optimization his exist and new structural elements. A model of optoelectronic electrodrive with laser-ultrasound cognitive transformation of energy and information is investigated. Model includes following basic elements: electromotor, driving a working mechanism; measuring-information complex, controlling and operating electromotor; amplifier on basis multi-modes solid laser with ultrasound quality modulator (UQML); transformer of laser pulses into voltage either current or magnetic field of electromotor. Researches dynamics of generating depend on pumping power and ultrasound intensity executioned on the rubin laser. Transition characteristic of electrodrive is defines by inertia of electromechanic elements, considerably exceed inertia of optoelectronic equipments. Inertia of electrodrive smooth out pulses of frequency-impulse energy (FIE). When estimation transition characteristic of electrodrive, take into account his inertia, FIE of laser radiation was accepted quasyconstant in time interval constant energy of pumping source and estimates alteration of rotation frequency and current force of electromotor were conducting on basic laws Kirchgof and Newton in approximation constant current by medium Matlab, Simulink. In the absence of ultrasound UQML radiates a chaotic optical impulse. By ultrasound control UQML passes into establish regime of frequency-impulse radiation. Repetition frequency of regular pulses is determination by pumping level when ultrasound power is constant, but did not depend on ultrasound frequency. Examined questions: self-regulation frequency-pulse generation, cognitive transformation of UQML; dynamics of electrodrive (ED) with UQML; equivalent powers sources of frequency-pulse and constant current; inertness ED with UQML; structure scheme of automatic ED with UQML. Self-regulation of UQML attach to increase energy-efficiency, possibility automatical of electrodrive.

Large-angle Lorentz Four-dimensional scanning transmission electron microscopy for simultaneous local magnetization, strain and structure mapping

Small adjustments in atomic configurations can significantly impact the magnetic properties of matter. Strain, for instance, can alter magnetic anisotropy and enable fine-tuning of magnetism. However, the effects of these changes on nanoscale magnetism remain largely unexplored. In particular, when strain fluctuates at the nanoscale, directly linking structural changes with magnetic behavior poses a substantial challenge. Here, we develop an approach, LA-Ltz-4D-STEM, to map structural information and magnetic fields simultaneously at the nanoscale. This approach opens avenues for an in-depth study of structure-property correlations of magnetic materials at the nanoscale. We applied LA-Ltz-4D-STEM to image strain, atomic packing, and magnetic fields simultaneously in a deformed amorphous ferromagnet with complex strain variations at the nanoscale. An anomalous magnetic configuration near shear bands, which reside in a magnetostatically high-energy state, was observed. By performing pixel-to-pixel correlation of the different physical quantities across a large field of view, a critical aspect for investigating industrial ferromagnetic materials, the magnetic moments were classified into two distinct groups: one influenced by magnetoelastic coupling and the other oriented by competition with magnetostatic energy.