Magnetostatic Research Articles

3D Magnetization Textures: Toroidal Magnetic Hopfion Stability in Cylindrical Samples.

Topologically non-trivial magnetization configurations in ferromagnetic materials on the nanoscale, such as hopfions, skyrmions, and vortices, have attracted considerable attention of researchers during the last few years. In this article, by applying the theory of micromagnetism, I demonstrate that the toroidal hopfion magnetization configuration is a metastable state of a thick cylindrical ferromagnetic nanodot or a nanowire of a finite radius. The existence of this state is a result of the competition among exchange, magnetostatic, and magnetic anisotropy energies. The Dzyaloshinskii-Moriya exchange interaction and surface magnetic anisotropy are of second importance for the hopfion stabilization. The toroidal hopfion metastable magnetization configuration may be reached in the process of remagnetizing the sample by applying an external magnetic field along the cylindrical axis.

3D BIOMIMETIC CONSTRUCTS STEER STEM CELL COMMITMENT BY SYNERGISTIC MODULATION OF BIOPHYSICAL CUES AND GROWTH FACTOR SIGNALLING

Tendon diseases are prevalent health concerns for which current therapies present limited success, in part due to the intrinsically low regenerative ability of tendons. Therefore, tissue engineering presents a potential to improve this outcome. Here, we hypothesize that a concurrent control over both biophysical and biochemical stimuli will boost the tenogenic commitment of stem cells, thus promoting regeneration. To achieve this, we combine molecularly imprinted nanoparticles (MINPs), which act as artificial amplifiers for endogenous growth factor (GF) activity, with bioinspired anisotropic hydrogels2 to manufacture 3D tenogenic constructs. MINPs were solid phase-imprinted using a TGF-β3 epitope as template and their affinity for the target was assessed by SPR and dot blot. Magnetically-responsive microfibers were produced by cryosectioning electrospun meshes containing iron oxide nanoparticles. The constructs were prepared by encapsulating adipose tissue-derived stem cells (ASCs), microfibers, and MINPs within gelatin hydrogels, while aligning the microfibers with an external magnetostatic field during gelation. This allows an effective modulation of hydrogel fibrillar topography, mimicking the native tissue's anisotropic architecture. Cell responses were analyzed by multiplex immunoassay, quantitative polymerase chain reaction, and immunocytochemistry. MINPs showed an affinity for the template comparable to monoclonal antibodies. Encapsulated ASCs acquired an elongated shape and predominant orientation along the alignment direction. Cellular studies revealed that combining MINPs with aligned microfibers increased TGF-β signaling via non-canonical Akt/ERK pathways and upregulated tendon-associated gene expression, contrasting with randomly oriented gels. Immunostaining of tendon-related proteins presented analogous outcomes, corroborating our hypothesis.Our results thus demonstrate that microstructural cues and biological signals synergistically direct stem cell fate commitment, suggesting that this strategy holds potential for improving tendon healing and might be adaptable for other biological tissues. The proposed concept highlights the GF-sequestering ability of MINPs which allows a cost-effective alternative to recombinant GF supplementation, potentially decreasing the translational costs of tissue engineering strategies.Acknowledgements: The authors acknowledge the funding from the European Union's Horizon 2020 under grant No. 772817; from FCT/MCTES for scholarships PD/BD/143039/2018 & COVID/BD/153025/2022 (S.P.B.T.), and PD/BD/129403/2017 (S.M.B.), co-financed by POCH and NORTE 2020, under the Portugal 2020 partnership agreement through the European Social Fund, for contract 2020.03410.CEECIND (R.M.A.D.) and project 2022.05526.PTDC; and from Xunta de Galicia for grant ED481B2019/025 (A.P.).

GPGPU Programming for Dipolar Field Calculation

Abstract Accelerating computational processes is paramount in numerical infrastructure development, particularly in applications such as the finite element method (FEM) and extensive calculations for simulating 3D processes in materials. In this work, we introduce a novel technique for computing the magnetostatic field of an ellipsoid particle, leveraging CUDA on a graphical card for parallel processing. The implementation on a GPU resulted in a remarkable 20-fold improvement in calculation speed. This achievement not only expedites research tasks, but also enables the exploration of larger and more intricate simulations, facilitating quicker model refinements and deeper insights into material behaviours under various conditions. The utilization of GPU computing aligns with the broader trend in scientific research and engineering, offering a versatile solution for diverse computational challenges beyond this specific task of magnetism. Overall, our work contributes to the ongoing effort to harness high-performance computing (HPC) technologies for accelerated and more efficient simulations in materials science and related fields.

Promising methods for improving the radio-frequency ion thruster performance

Improving the reliability and efficiency of available electric propulsion schemes is one of the priority areas of space technology development. In particular, this should be done for ensuring the guaranteed removal of spacecraft to a disposal orbit at the end of their active life, which, in turn, will slow down the growth in the number of space debris objects in the most exploited regions of near-Earth space. The paper considers ways to improve the power and mass efficiency of one of the modern electric propulsion types - a radio-frequency ion thruster with an inductive radio-frequency discharge. Using an engineering physico-mathematical model, computational studies were performed to optimize the shape of the radio-frequency ion thruster main components, namely the discharge chamber and the grids of ion-extraction system. The thrust of the thruster was used as the optimization criterion; it was determined from the calculated ion density distributions in the radio-frequency discharge plasma. Such an approach to refine the performance improvement methods has not previously been applied to radio-frequency ion thruster. The ion density distributions, as well as the thruster integral characteristics determined from them, such as the thrust, total ion current from the thruster, propellant utilization factor, ionization cost and a number of others, were calculated for two actual standard sizes of radio-frequency ion thruster with the beam diameters of 80 mm and 160 mm, which can be used to solve the problems listed above. Besides, for the defined optimal configurations of thruster with two standard sizes the calculations were made to assess the possibility for increasing the thruster integral characteristics by applying an additional magnetostatic field in the radio-frequency discharge region. The study revealed the possibility of noticeable performance improvement compared to the basic radio-frequency ion thruster design with hemispherical discharge chamber and flat grids of the ion-extraction system.

Magnetostatic Field Induced by Mechanical Deformations

AbstractA general expression for the magnetostatic field generated by mechanical deformations to a ferromagnetic material in the continuum description is derived. Linearization with respect to the displacement vector is shown to be well defined. To demonstrate the use of the formulation, two examples are discussed. First, a complete derivation of the magneto‐rotation coupling for a uniformly magnetized film is given. Second, the lowest asymmetric mode of Lamb waves propagating through a magnetic vortex is shown to induce an in‐plane magnetostatic field localized around the vortex core.

Quantum Hall coherent perfect absorption in graphene

100%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$100\\%$$\\end{document} absorption in a two-dimensional electron gas (2DEG) with Dirac spectrum is demonstrated to be obtained by controlling the interference of multiple incident radiations, referred to as coherent perfect absorption (CPA). However, when a 2DEG such as graphene is exposed to a magnetostatic bias, it resonantly could absorb electromagnetic radiation by transitions of its Dirac electrons between non-equidistant and nonlinear Landau levels. Here, the magneto-optical terahertz (THz) CPA in graphene under the quantum Hall effect (QHE) regime at both strong and subtesla magnetostatic bias fields is addressed. Our findings show that an effective magneto-optical surface conductivity corresponding to right- and left-handed circular (RHC- and LHC) polarizations could model a magneto-tunable CPA in graphene in THz range. Significantly, graphene under QHE regime reveals different tunable CPA properties for each circularly polarized beams by the intensity of the applied magnetic bias. Moreover, it is observed that different phase modulations at CPA frequencies are achieved for RHC and LHC polarizations. Considering the maximum efficiency for a 2D absorber, our results demonstrate the magnetostatic tuning of CPA in 2D Dirac materials for long-wavelength sensing applications and signal processing.

Electron nonlinear dynamics in a compact accelerator based on the circular rotating TM110 mode

The present study investigates the electron autoresonant acceleration using the rotating transverse magnetic mode TM110 microwave field within an inhomogeneous magnetostatic field. Differential equations governing the evolution of the phase shift between the electron’s angular position and the angle at which transferred power is maximized, the total electron energy, and the longitudinal electron velocity are derived. Magnetic field profiles required to sustain electron acceleration are determined. The results demonstrate that an electron injected along the cavity axis with an energy of 30keV can be accelerated up to approximately 200keV, using an electric field amplitude of 20kV/cm, a frequency of 8GHz, and a linear magnetic field profile. Additionally, we consider the case of electron acceleration under exact resonance conditions, and the corresponding magnetic field profile predicted by the model is obtained.The findings presented in this paper are valuable for the design of RF accelerators utilizing the circular rotating TM110 mode, particularly in applications such as x-ray sources for medical purposes, airport security, and various other fields.

Simulation of electron transport and secondary emission in a photomultiplier tube and experimental validation

The electron amplification and transport within a photomultiplier tube (PMT) has been investigated by developing an in-house Monte Carlo simulation code. The secondary electron emission in the dynodes is implemented via an effective electron model and the Modified Vaughan’s model, whereas the transport is computed with the Boris leapfrog algorithm. The PMT gain, rise time and transit time have been studied as a function of supply voltage and external magnetostatic field. A good agreement with experimental measurements using a Hamamatsu R13408-100 PMT was obtained. The simulations have been conducted following different treatments of the underlying geometry: three-dimensional, two-dimensional and intermediate (2.5D). The validity of these approaches is compared. The developed framework will help in understanding the behavior of PMTs under highly intense and irregular illumination or varying external magnetic fields, as in the case of prompt gamma-ray measurements during pencil-beam proton therapy; and aid in optimizing the design of voltage dividers with behavioral circuit models.

Physics-Informed Neural Networks for Solving 2-D Magnetostatic Fields

Physics-informed neural network (PINN) has shown great potential in the inverse and parametric designing problems in electrical engineering. Moreover, most existing works on PINN are dedicated to computational fluids, and very few attentions have been paid to static and low-frequency electromagnetic near fields with multiple media in electrical engineering applications. In this work, a PINN for solving two-dimensional (2D) magnetostatic fields in electromagnetic devices and systems is proposed. The magnetic field intensity and the magnetic vector potential are solved by training a neural network which encodes partial differential equations and boundary conditions as residuals. The computation of the spatial derivatives of media constitutive parameters, which negatively impacts the training of PINN, is eliminated. A mesh-assisted non-uniform sampling method for the selection of collocation points is proposed to further improve the performance of PINN. The proposed PINN is verified by comparing its results with those of the finite element method in two 2D magnetostatic case studies. It is expected that this work will promote further applications of PINN in the modelling, numerical analysis, and parametric design of electromagnetic devices and systems.

Hybrid Superposition Integral—Poisson Solver Method for the Magnetostatic Field in Finite Element Micromagnetic Solvers

Hybrid Superposition Integral—Poisson Solver Method for the Magnetostatic Field in Finite Element Micromagnetic Solvers

Magnetic energy of interaction between a synthetic antiferromagnet and a free layer of a spin-tunnel element

An exact expression is found for the magnetostatic energy of interaction of a synthetic antiferromagnet with a free layer of a spin-tunnel element, the ferromagnetic layers of which have the shape of strongly oblate ellipsoids of revolution. It has been established that the exact value of this interaction energy can differ significantly from the usual value, which is calculated using the expression for the demagnetizing field. The parameters are calculated for which the complete compensation of the magnetic interaction of a synthetic antiferromagnet occurs.

Graphene-based terahertz antenna with polarization reconfiguration

This article presents the design of a terahertz antenna with the ability to reconfigure its polarization using graphene’s anisotropic properties. By applying a DC magnetic flux, the graphene conductivity tensor can be transformed into a non-diagonal tensor. Conversely, the magnetic bias can be switched off to revert the tensor to a diagonal state. This approach allows the antenna to switch between linear and circular polarizations, making it highly versatile for terahertz applications. Additionally, by altering the direction of the applied DC magnetic bias, one can select the rotation direction of circular polarization between left and right hand. The feeding line and ground plane of the antenna are made of silver metal, and its behavior in the terahertz band is described using the Modified Relaxation-Effect model, which is more accurate than the skin effect model for this band. The finite element numerical method is utilized to analyze the antenna, which yields results consistent with the design predictions. The antenna’s impedance bandwidth spans 2.8 to 3.22 terahertz for linear polarization and 2.9 to 3.18 THz for circular polarization. The antenna’s maximum gain is 6 dB for linear polarization and 5 dB for circular polarization. The axial ratio for circular polarization is 1.36 in the middle of the band, which is below the 3 dB threshold for circular polarization. The antenna produces directive patterns for both linear and circular polarizations. The key innovation of this antenna design lies in its unique utilization of a magnetostatic field to achieve reconfiguration in the terahertz graphene dielectric resonator antenna, a method that has not been previously documented in literature.

External magnetic field have significant effects on diversity of magnetotactic bacteria in sediments from Yangtze River, Chagan Lake and Zhalong Wetland in China

Magnetotactic bacteria (MTB) can rapidly relocate to optimal habitats by magnetotaxis, and play an important role in iron biogeochemical cycling. This study aimed to evaluate the contribution of the external magnetostatic field to the diversity of MTB in freshwater sediments from Yangtze River (Changjiang River, CJ), Chagan Lake (CGH) and Zhalong Wetland (ZL). The magnetic field intensity was tightly associated with the community richness of MTB in CJ, whereas it was closely related to the diversity of MTB in CGH and ZL (p < 0.05), elucidating a significant variation in the community composition of MTB. Magnetic exposure time appeared more significant correlation with community richness than diversity for MTB in CJ and CGH (p < 0.05), while an opposite relationship existed in ZL (p < 0.01). Herbaspirillum (93.81–96.48 %) dominated in the sediments of these surfacewatesr regardless of waterbody types, while it shifted to Magnetospirillum in ZL under 100 Gs magnetic field. The network connectivity and stability of MTB deteriorate with the increase of magnetic field intensity. Functional analysis showed that the Two-component system and ABC transporter system of MTB obviously responded to magnetic field intensity and exposure time. Our findings will pave the way to understanding the response mechanism of MTB community in freshwater sediments to the external magnetostatic field.

Hyperfine transition induced by atomic motion above a paraffin-coated magnetic film

We measured transitions between the hyperfine levels of the electronic ground state of potassium-39 atoms (transition frequency: 460 MHz) as the atoms moved through a periodic magneto-static field produced above the magnetic-stripe domains of a magnetic film. The period length of the magnetic field was 3.8 µm. The atoms were incident to the field as an impinging beam with the most probable velocity of 550 m s−1 and experienced a peak oscillating field of 20 mT. Unwanted spin relaxation caused by the collisions of the atoms with the film surface was suppressed by the paraffin coating on the film. We observed increasing hyperfine transition probabilities as the frequency of the field oscillations experienced by the atoms increased from 0 to 140 MHz for the atomic velocity of 550 m s−1, by changing the incident angle of the atomic beam with respect to the stripe domains. Numerical calculation of the time evolution of the hyperfine states revealed that the oscillating magnetic field experienced by the atoms induced the hyperfine transitions, and the main process was not a single-quantum transition but rather multi-quanta transitions.

AC magnetic trap for cold paramagnetic molecules

Strong-field-seeking states are the lowest-energy configurations for paramagnetic molecules in the magnetic field. Molecules in strong-field-seeking states cannot be trapped in a magnetostatic field because a magnetostatic maximum in free space is not allowed. In this paper, we propose an AC magnetic trap composed of two pairs of Helmholtz coils. The spatial magnetic field distribution is numerically calculated and the time-sequential control is depicted. We investigate the influence of the switching frequency and the electric current in the coils on the performance of our trap. Variations of the location and phase-space distribution during a whole switching cycle are simulated. Finally, we study the impact of time during which the field is switched off on the number of captured molecules in a switching cycle.

A study of the magnetic properties of LaNi5 and their effect on hydrogen desorption under the action of a magnetostatic field

A study of the magnetic properties of LaNi5 intermetallic compoundand and their effect on desorption reaction was carried out as a function of temperature. A Vibrating Sample Magnetometer (VSM) was used for the magnetic measurements and a Metal Hydrogen Reactor (MHR) supplied by a constant current through a coil was used for the hydrogen desorption reaction under the action of a magnetostatic field. Then, the hysteresis cycle, the first magnetization curve, the thermo-magnetization curves and the desorbed hydrogen mass were determined. The results showed that the application of a magnetic field corresponding to the magnetization at saturation Ms at a given temperature improved the hydrogen desorption reaction by the LaNi5.

Inductive sensing of magnetic microrobots under actuation by rotating magnetic fields.

The engineering space for magnetically manipulated biomedical microrobots is rapidly expanding. This includes synthetic, bioinspired, and biohybrid designs, some of which may eventually assume clinical roles aiding drug delivery or performing other therapeutic functions. Actuating these microrobots with rotating magnetic fields (RMFs) and the magnetic torques they exert offers the advantages of efficient mechanical energy transfer and scalable instrumentation. Nevertheless, closed-loop control still requires a complementary noninvasive imaging modality to reveal position and trajectory, such as ultrasound or X-rays, increasing complexity and posing a barrier to use. Here, we investigate the possibility of combining actuation and sensing via inductive detection of model microrobots under field magnitudes ranging from 100 s of microtesla to 10 s of millitesla rotating at 1 to 100 Hz. A prototype apparatus accomplishes this using adjustment mechanisms for both phase and amplitude to finely balance sense and compensation coils, suppressing the background signal of the driving RMF by 90 dB. Rather than relying on frequency decomposition to analyze signals, we show that, for rotational actuation, phase decomposition is more appropriate. We demonstrate inductive detection of a micromagnet placed in two distinct viscous environments using RMFs with fixed and time-varying frequencies. Finally, we show how magnetostatic selection fields can spatially isolate inductive signals from a micromagnet actuated by an RMF, with the resolution set by the relative magnitude of the selection field and the RMF. The concepts developed here lay a foundation for future closed-loop control schemes for magnetic microrobots based on simultaneous inductive sensing and actuation.

Static magnetic signature of a ghost-ship propulsor system as a composite ferromagnetic medium

In this paper, it is shown that the static magnetic signature of a propulsor belonging to a ghost ship, whose hull is made of fiberglass, can be calculated by regarding it as a composite ferromagnetic medium. The calculation of the magnetic signature in the static regime is carried out using finite-element method simulations and according to a simple analytical model based on the concepts of volume averaged magnetization arising from a source magnetic field, volume averaged permeability, surface magnetic charges, and the demagnetization tensor applied to a composite magnetic medium. Using targeted simulations, it is demonstrated that the magnetostatic field of demagnetizing nature forming inside the propulsor almost cancels the contribution of the volume averaged magnetization. From the interplay between the numerical simulations and the analytical model, the elements of the demagnetization tensor in the region filled by the propulsor are locally calculated, and their role in determining the localization effects of the magnetic signature is discussed. By replacing the original ferromagnetic materials with weakly ferromagnetic ones, it is shown that, in the underwater region outside the propulsor, the magnetic signature drop is 64%. This analysis suggests an experimental way to use a simple passive method to minimize the magnetic signature of a propulsor as an alternative to more complex and time-consuming methods, such as the deperming and degaussing methods, widely employed to reduce the magnetic signature of ships and underwater objects in military applications.

Effect of TaN buffer layer on the sensitivity of ASIC-integrated AMR sensors

This study investigates the impact of a TaN buffer layer on the performance of ASIC-integrated Anisotropic Magnetoresistive (AMR) position sensors. Our findings demonstrate that the inclusion of a TaN buffer layer significantly enhances the sensitivity and stability of the sensors, with a measured sensitivity of 0.678 ± 0.03 Gauss/mV. In contrast, devices without the buffer layer exhibit a notable decline in sensitivity, decreasing to 0.165 ± 0.02 Gauss/mV after 450℃ annealing. In addition, AMR sensors fabricated on non-ASIC substrates showed no such deterioration. Magneto-optical Kerr effect (MOKE) measurements reveal that the change in sensitivity is primarily attributed to variations in the anisotropy field. We propose that the increased anisotropy field is a result of magnetostatic energy induced by alterations in the PECVD-deposited SiO2 surface granular structure, supported by surface morphology characterization and X-ray diffraction experiments. These findings highlight the critical role of the TaN buffer layer in optimizing the performance and stability of ASIC-integrated AMR sensors.

Relativistic laser third-harmonic generation from magnetized plasmas under a tapered magnetostatic wiggler

In this work, the third harmonic generated by Gaussian laser pulse propagating in magnetized plasma under the impact of tapered magnetostatic wiggler field is studied. Fundamental equations for analysis of third-harmonic generation by employing the equation of motion, the continuity equation, and the perturbation technique for Gaussian laser pulse in a weakly relativistic regime and the attendance of a wiggler magnetic field are derived. Additionally, the influences of laser strength, wiggler field, plasma frequency, and the δ-parameter on the third-harmonic generation are investigated. The results show that the amount of wiggler frequency required to generate the third harmonic decreases with an increase in the laser strength parameter. Aside from that, the plasma frequency is enhanced with increasing wiggler frequency. Furthermore, it is observed that the efficiency of the generated third harmonic decreases with increasing δ-parameter. In addition, it is found that the efficiency of the generated third harmonic also depends on the time, and the maximum efficiency occurs while the phase matching condition is satisfied. Furthermore, it is seen that the efficiency of the generated third harmonic enhances with increasing plasma frequency. Moreover, it is revealed that the Gaussian laser pulse amplitude has a negligible effect on the third-harmonic efficiency at very low intensities.