Magnetic Field Research Articles

Suppression of magnetic vortex losses in submicron NbN coplanar waveguide resonators

We present a method for improving the performance of microwave coplanar resonators in magnetic fields, by using narrow superconducting strips of width close to the London penetration depth. In a range of low fields, the narrow strips inhibit the presence of magnetic vortices, thus preventing the generation of losses caused by their motion, leading to enhanced resistance to magnetic fields. Our method provides a more straightforward solution compared to previously proposed techniques designed to restrict vortex motion, holding potential for the development of improved devices based on microwave resonators.

Study of Compact Traveling-Standing Wave Relativistic Folded Waveguide Oscillator With Low Magnetic Field Operation

Abstract In this article, a compact Traveling-standing Wave Relativistic Folded Waveguide Oscillator (TSW-RFWO) is proposed, leveraging a 0.3 T guiding magnetic field to address the crucial needs for miniaturization and practicality in high-power microwave systems. The study conducts a thorough analysis of the electromagnetic characteristics of the TSW-RFWO. Its internal traveling-standing wave signal is analyzed. Utilizing the traveling-standing wave slow-wave structure (TSW-SWS), the TSW-RFWO obtains a low Qe (external quality factor) of 39. The necessity of compacting the high-power device under low magnetic guiding field is analyzed. Employing a 300 kV, 400 A circular electron beam within a 0.3 T guiding magnetic field, PIC simulations indicate a potential output power of 57 MW at 2.74 GHz, achieving a peak efficiency of 47.5%.

Investigation of thermodynamic properties of bilayer graphene under dual gating with perpendicular magnetic field

Investigation of thermodynamic properties of bilayer graphene under dual gating with perpendicular magnetic field

Effect of alternative magnetic fields with different intensities on microstructure and mechanical properties of M50 steel during vacuum arc remelting

Effect of alternative magnetic fields with different intensities on microstructure and mechanical properties of M50 steel during vacuum arc remelting

Geophysical Coupling Before Three Earthquake Doublets Around the Arabian Plate

In this study, we analysed lithospheric, atmospheric, and top-side ionospheric magnetic field data six months before the three earthquake doublets occurred in the last ten years around the Arabian tectonic plate. They occurred in 2014, close to Dehloran (Iran), in 2018, offshore Kilmia (Yemen) and in 2022, close to Bandar-e Lengeh (Iran). For all the cases, we considered the equivalent event in terms of total released energy and mean epicentral coordinates. The lithosphere was investigated by calculating the cumulative Benioff strain with the USGS earthquake catalogue. Several atmospheric parameters (aerosol, SO2, CO, surface air temperature, surface latent heat flux humidity, and dimethyl sulphide) have been monitored using the homogeneous data from the MERRA-2 climatological archive. We used the three-satellite Swarm constellation for magnetic data, analysing the residuals after removing a geomagnetic model. The analysis of the three geo-layers depicted an interesting chain of lithosphere, atmosphere, and ionosphere anomalies, suggesting a geophysical coupling before the Dehloran (Iran) 2014 earthquake. In addition, we identified interesting seismic accelerations that preceded the last 20 days, the Kilmia (Yemen) 2018 and Bandar-e Lengeh (Iran) 2022 earthquake doublets. Other possible interactions between the geolayers have been observed, and this underlines the importance of a multiparametric approach to properly understand a geophysical complex topic as the preparation phase of an earthquake.

Numerical study of turbulent eddy self-interaction in tokamaks with low magnetic shear. Part II: Nonlinear simulations.

Abstract Using local nonlinear gyrokinetic simulations and building up on linear results from a companion paper (Vol\v{c}okas, 2024), we demonstrate that turbulent eddies can extend along magnetic field lines for hundreds of poloidal turns in tokamaks with weak or zero magnetic shear $\hat{s}$. We observe that this parallel eddy length scales inversely with magnetic shear and at $\hat{s}=0$ is limited by the thermal speed of electrons $v_{th,e}$. We examine the consequences of these ``ultra long" eddies on turbulent transport, in particular, how field line topology mediates strong parallel self-interaction. Our investigation reveals that, through this process, field line topology can strongly affect transport. It can cause transitions between different turbulent instabilities and in some cases triple the logarithmic gradient needed to drive a given amount of heat flux. We also extensively study a novel ``eddy squeezing" effect introduced in (Vol\v{c}okas, 2023), which reduces the perpendicular size of eddies and their ability to transport energy, thus representing a novel approach to improve confinement. Finally, we investigate the triggering mechanism of Internal Transport Barriers (ITBs) using low magnetic shear simulations, shedding light on why ITBs are often easier to trigger where the safety factor has a low-order rational value.

Design of Remote-Controllable Diels-Alder Platform on Magnetic Nanoparticles via Layer-by-Layer Assembly for AC Magnetic Field-Triggered Drug Release.

Diels-Alder chemistry was exploited to develop a remote-controllable drug release platform on magnetic nanoparticles (MNPs). For this purpose, MNPs were decorated with anionic poly(styrenesulfonic acid-co-furfuryl methacrylate) (poly(SS-co-FMA)) and cationic poly(allylamine hydrochloride) by layer-by-layer assembly. The decorated MNPs successfully underwent DA reaction to produce covalent bonding between FMA (diene) and maleimide (dienophile)-terminated model drug. Thermal treatment above 80 °C caused the retro Diels-Alder reaction (rDA) between FMA and the drug, resulting in drug release. The retro DA could be also achieved by applying an alternating-current (AC) magnetic field to the decorated MNPs. This could spatially limit the heat generation around MNP without heating entire system. Drug release could be also accelerated with the irradiation time when a threshold temperature was met or exceeded the required energy for rDA reaction. Our results highlight the potential of DA chemistry as a new strategy to provide a remote controllable drug release platform for improving the therapeutic efficiency.

Magnetic Hercules Swarm for Precise and Effective Deep Biofilm Eradication

AbstractOver the past decade, significant advancements in micro‐nano robots have enabled non‐invasive operations in hazardous, confined environments, particularly targeting persistent bacterial biofilms in hard‐to‐reach areas. However, many of these robots are limited by poor magnetic properties, hindering their effectiveness against biofilms. This study proposes a novel strategy using a swarm with strong magnetic effects (Hercules swarm) combined with near‐infrared (NIR) light for effective biofilm eradication. Carbonyl iron particles coated with polydopamine (CI@PDA), averaging ≈3 µm in diameter, demonstrate clustering and significant magneto‐force under a rotating magnetic field due to their large magnetic saturation. This enables the Hercules swarm to achieve rapid delivery (100 mm s−1), efficient cargo transport (carrying twice its own weight), and effective catheter clearance (1 mm min−1). The controllable motion and high photothermal activity enable precise biofilm eradication without toxic agents. The aggregation of magnetic particles into chains and their rotation are explored by improved particle dynamic model. Simulations also reveal enhanced fluid convection and mechanical pressure around the particle chain. Due to its easy operation, straightforward controllability, and environmental compatibility, the magnetic Hercules swarm emerges as a promising treatment modality for eliminating biofilms entrenched within intricate, narrow, and convoluted medical implants or industrial conduits.

Evolution of critical current density in CaKFe4As4 with La-doping

Abstract Single crystals of (Ca1-xLax)KFe4As4 (0 ≤ x ≤0.16) have been grown by using the self-flux method, and the evolution of physical properties including the critical current density (Jc) with La-doping has been investigated. Tc decreases monotonically with increasing x, while Jc at the same temperature and magnetic field increases initially and reach its maximum at x = 0.082. The increase in Jc is more obvious at low temperatures and high fields. At T = 5 K and H = 40 kOe, Jc reaches 0.34 MA/cm2, which is ~4 times larger than that for pure crystals. It is also found that anomalous temperature dependence of Jc in CaKFe4As4 is wiped away as the La content is increased. However, Jc shows non-monotonic field dependence (peak effect) at high fields in crystals with large x. In addition, we found that despite weak anisotropy of Hc2, there is extremely large anisotropy of Jc up to ~15, which is most likely caused by novel planar defects in the crystal, similar to CaKFe4As4. Jc characteristics in (Ca1-xLax)KFe4As4 with disorder outside FeAs planes is compared with that in CaK(Fe1-xCox)4As4 with disorder within FeAs planes.

Modeling and Simulation of Electric and Magnetic Fields of a Short Dipole Antenna at Low Frequencies in the Far Field

Modeling and Simulation of Electric and Magnetic Fields of a Short Dipole Antenna at Low Frequencies in the Far Field

Rotary excitation of non-sinusoidal pulsed magnetic fields: Towards non-invasive direct detection of cardiac conduction.

There is a need for high resolution non-invasive imaging methods of physiologic magnetic fields. The purpose of this work is to develop a MRI detection approach for non-sinusoidal magnetic fields based on the rotary excitation (REX) mechanism which was previously successfully applied for the detection of oscillating magnetic fields in the sub-nT range. The new detection concept was examined by means of Bloch simulations, evaluating the interaction effect of spin-locked magnetization and low-frequency pulsed magnetic fields. The REX detection approach was validated under controlled conditions in phantom experiments at 3 T. Gaussian and sinc-shaped stimuli were investigated. In addition, the detection of artificial fields resembling a cardiac QRS complex, which is the most prominent peak visible on a magnetocardiogram, was tested. Bloch simulations demonstrated that the REX method has a high sensitivity to pulsed fields in the resonance case, which is met when the spin-lock frequency coincides with a non-zero Fourier component of the stimulus field. In the experiments, we found that magnetic stimuli of different durations and waveforms can be distinguished by their characteristic REX response spectrum. The detected REX amplitude was proportional to the stimulus peak amplitude (R2 > 0.98) and the lowest field detection was 1 nT. Furthermore, the detection of QRS-like fields with varying QRS durations yielded significant results in a phantom setup (p < 0.001). REX detection can be transferred to non-sinusoidal pulsed magnetic fields and could provide a non-invasive, quantitative tool for spatially resolved assessment of cardiac biomagnetism. Potential applications include the direct detection and characterization of cardiac conduction.

Solar active region evolution and imminent flaring activity through color-coded visualization of photospheric vector magnetograms

Context. The emergence of magnetic flux, its transition to complex configurations, and the pre-eruptive state of active regions are probed using photospheric magnetograms. Aims. Our aim is to pinpoint different evolutionary stages in emerging active regions, explore their differences, and produce parameters that could advance flare prediction using color-coded maps of the photospheric magnetic field. Methods. The three components of the photospheric magnetic field vector are combined to create color-combined magnetograms (COCOMAGs). From these, the areas occupied by different color hues are extracted, creating appropriate time series (color curves). These COCOMAGs and color curves are used as proxies of the active region evolution and its complexity. Results. The morphology of COCOMAGs showcases typical features of active regions, such as sunspots, plages, and sheared polarity inversion lines. The color curves represent the area occupied by photospheric magnetic field of different orientation and contain information pertaining to the evolutionary stages of active regions. During emergence, most of the region area is dominated by horizontal or highly inclined magnetic field, which is gradually replaced by more vertical magnetic field. In complex regions, large parts are covered by highly inclined magnetic fields, appearing as abrupt color changes in COCOMAGs. The decay of a region is signified by a domination of vertical magnetic field, indicating a gradual relaxation of the magnetic field configuration. The color curves exhibit a varying degree of correlation with active region complexity. Particularly the red and magenta color curves, which represent strong, purely horizontal magnetic field, are good indicators of future flaring activity. Conclusions. Color-combined magnetograms facilitate a comprehensive view of the evolution of active regions and their complexity. They offer a framework for the treatment of complex observations and can be used in pattern recognition, feature extraction, and flare-prediction schemes.

Quiescent Solar Wind Regions in the Near-Sun Environment: Properties and Radial Evolution

Regions of magnetic fields with near-radial, Parker-spiral-like geometry known as quiescent regions have been observed in Parker Solar Probe data. These regions have very low δ B/〈∣B∣〉 compared to nonquiescent solar wind at the same heliocentric distances. Quiescent regions are observed to have lower solar wind bulk speeds, lower proton temperatures, and lower proton density. Inside of 15 solar radii ( R ⊙ ), identified quiescent regions show distinct thermal properties, having higher proton temperature anisotropies and lower parallel plasma betas compared to switchback patches observed at the same heliocentric distances. When placed on R -versus-β ∥p plots (where R is the proton temperature anisotropy), quiescent region solar wind is shown to be more stable to proton cyclotron and firehose instabilities than nonquiescent solar wind at the same heliocentric distances. It is shown that quiescent regions evolve similarly to the surrounding nonquiescent solar wind, but quiescent solar wind begins at a different location in the R -versus-β ∥p parameter space, suggesting that these regions have separate origins from the more turbulent nonquiescent solar wind. Namely, enhanced temperature anisotropies and enhanced magnetic field strength may be consistent with magnetic field lines that have undergone less magnetic field expansion compared to nonquiescent wind at the same heliocentric distances.

Longitudinal (α33) and transverse(α31) dynamic magnetoelectric hysteretic response for CoFe1.88Dy0.12O4–K0.5Na0.5NbO3 lead-free multiferroic laminates

The magnetoelectric (ME) laminate structures of CoFe1.88Dy0.12O4 (CFDO, Ferrite) and K0.50Na0.50NbO3 (KNN, ferroelectric/piezoelectric) phases were fabricated by silver epoxy bonding technique and tested the ME response in longitudinal and transverse mode. The CFDO reveals the cubic spinel structure while KNN reveals the perovskite orthorhombic crystal structures having dense microstructure. The CFDO confirms the phase segregation of the DyFeO3ortho-ferrite phase, while the KNN lead-free ceramic showed the Curie temperature of 416 °C, 13µC/cm2 maximum polarization, 25,296 × 10-15 m2/N figure of merit, piezoelectric charge coefficient d33 of 47 pC/N. The longitudinal (α33) and transverse (α31) dynamic magnetoelectric response is studied to figure out the effective magnetic field direction to get better values of magnetoelectric voltage sensitivity i.e. αME. Both modes revealed the hysteretic behavior i.e. lagging of ME voltage response to an applied magnetic field which evidences a true multiferroic character of CFDO/KNN laminates. Remarkably, the (CFDO /KNN/ CFDO) structure demonstrated a substantial magnetoelectric coefficient in LT (α31) mode of approximately 38.5 mV/cm·Oe at a magnetic field of 400 Oe and −37.55 mV/cm·Oe at a magnetic field of −400 Oe. Thus, here we present the magnetoelectric laminate structure of CFDO /KNN/ CFDO phases beneficial for magnetic field sensors.

A Data-driven Magnetohydrodynamic Simulation of the 2011 February 15 Coronal Mass Ejection from Active Region NOAA 11158

We present a boundary data-driven magnetohydrodynamic (MHD) simulation of the 2011 February 15 coronal mass ejection (CME) event of Active Region NOAA 11158. The simulation is driven at the lower boundary with an electric field derived from the normal magnetic field and the vertical electric current measured from the Solar Dynamics Observatory (SDO) Helioseismic Magnetic Imager vector magnetograms. The simulation shows the buildup of a pre-eruption coronal magnetic field that is close to the nonlinear force-free field extrapolation, and it subsequently develops multiple eruptions. The sheared/twisted field lines of the pre-eruption magnetic field show qualitative agreement with the brightening loops in the SDO Atmospheric Imaging Assembly (AIA) hot passband images. We find that the eruption is initiated by the tether-cutting reconnection in a highly sheared field above the central polarity inversion line and a magnetic flux rope with dipped field lines forms during the eruption. The modeled erupting magnetic field evolves to develop a complex structure containing two distinct flux ropes and produces an outgoing double-shell feature consistent with the Solar Terrestrial Relations Observatory B/Extreme UltraViolet Imager observation of the CME. The foot points of the erupting field lines are found to correspond well with the dimming regions seen in the SDO/AIA observation of the event. These agreements suggest that the derived electric field is a promising way to drive MHD simulations to establish the realistic pre-eruption coronal field based on the observed vertical electric current and model its subsequent dynamic eruption.

Forced flow reversal in ferrofluidic Couette flow via alternating magnetic field

Time-dependent boundary conditions are very common in natural and industrial flows and by far no exception. An example of this is the movement of a magnetic fluid forced due to temporal modulations. In this study, we used numerical methods to examine the dynamics of ferrofluidic wavy vortex flows (WVF2, with dominant azimuthal wavenumber m=2) in the counter-rotating Taylor–Couette system, which was subjected to time-periodic modulation/forcing in a spatially homogeneous magnetic field. In the absence of a magnetic field, all WVF2 states move in the opposite direction to the rotation of the inner cylinder, they are retrograde. However, when strength or frequency of the alternating magnetic field increases, the motion direction of the flow pattern changes. Thus, the alternating field provides a precise and controllable key parameter for triggering the system response and controlling the flow. Aside, we also observed intermittent behavior when one solution became unstable, leading to random transitions in both, the transition time and toward the different final solutions. Our findings suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which may have applications in the development of modern fluid devices in laboratory experiments. These findings provide a framework to study other types of magnetic flows driven by time-dependent forcing.

Manipulating microfluidic freezing phenomena of electrolytes using electromagnetic stimuli

We investigate the transients of freezing of a flowing electrolyte between cold microfluidic domain walls. We explore the novel effect of morphing the solidification characteristics of the flow system using externally applied electric and magnetic fields. The spatiotemporal evolution of solid–liquid (S–L) interface is simulated using arbitrary Lagrangian–Eulerian approach. We show that the solidification rate is highly influenced by advection effects, and for increasingly high liquid flow rates, solidification stops way before the event of channel closure. Due to electro-magneto-hydrodynamic interactions, a substantial decrease in channel closing time is observed with imposed fields. However, a considerably large electric field may lead to a significant increase in Joule heating, which marginally increases the channel closing time. The magnetic field is observed to produce smoother, curved frozen layers. The electric field tends to enhance the solidification rates more uniformly along the channel length, resulting in much flatter S–L front, hence trapping lesser liquid at channel closure. The results reveal that freezing kinetics in microfluidic devices can be morphed by using electric and magnetic fields, governed by the electric field number (En) and Hartmann number (Ha). The findings may be crucial for phase-change based microfluidic-systems, micro-castings, flow freezing valves, and diodes.

Medium Amplitude Field Susceptometry (MAFS) for magnetic nanoparticles

The linear dynamic susceptibility is arguably the most important property to specify the magnetization dynamics of a given system. Therefore, this quantity has been studied in great detail and the corresponding measurements known as susceptometry are well-established. Notwithstanding its relevance, the linear susceptibility is inherently limited to describe the magnetization response to weak external fields only. Here, we suggest the framework of Medium Amplitude Field Susceptometry (MAFS) to study the non-linear response which complements the linear susceptibility and provides additional information on the magnetic properties of the system and is applicable to magnetic fields of medium amplitudes. In particular, we introduce the general third-order nonlinear susceptibility χˆ3 as a central quantity that completely specifies the lowest-order non-linear response to arbitrary time-dependent magnetic fields. We show that response functions in medium amplitude oscillatory magnetic fields and parallel superposition susceptometry are contained in χˆ3 as special cases. Also included in χˆ3 are interesting intermodulation effects when the system is probed by a superposition of oscillating magnetic fields with different frequencies. We work out the explicit form of χˆ3 for several model systems for the dynamics of magnetic nanoparticles (MNPs). We expect this unifying framework to be not only of theoretical interest, but also useful for a deeper characterization of MNP systems, giving additional information on their suitability for various applications.

Simulated investigation of a ku-band relativistic magnetron with modified all-cavity axial extraction at a low magnetic field

Since its invention in 1921 by Hull, magnetrons have undergone rapid development, transitioning from low-power devices to high-power relativistic magnetrons (RMs). However, research on RMs has been predominantly confined to L-X bands until now. To explore the potential of RM in higher frequency bands and align with the trend toward miniaturization of high-power microwave sources, a Ku-band RM has been investigated in this paper. Theoretical analysis dictates the selection of 24 cavities for optimal performance at a low magnetic field. Utilizing a three-dimensional particle-in-cell simulation platform, we demonstrate that the RM can generate a microwave power of 116 MW at a resonant frequency of 13.717 GHz with an electron beam of 126 kV and 2.0 kA, under a magnetic field of 0.22 T, corresponding to a power conversion efficiency of 46%. The integration of a modified all-cavity axial extraction structure in the Ku-band RM allows for a minimized inner radius of the magnetic field system to approximately 25 mm, while maintaining a high-power microwave output.

Effects of 16.8-22.0 T high static magnetic fields on the development of zebrafish in early fertilization.

Despite some existing studies on the safety of high static magnetic fields (SMFs), the effects of ultra-high SMFs above 20.0 T for embryonic development in early pregnancy are absent. The objective of this study is to evaluate the influence of 16.8-22.0 T SMF on the development of zebrafish embryos, which will provide important information for the future application of ultra-high field magnetic resonance imaging (MRI). Two-hour exposure to homogenous (0 T/m) 22.0 T SMF, or 16.8 T SMFs with 123.25 T/m spatial gradient of opposite magnetic force directions was examined in the embryonic development of 200 zebrafish. Their body length, heart rate, spontaneous tail-wagging movement, hatching and survival rate, photomotor response, and visual motor response (VMR) were analyzed. Our results show that these ultra-high SMFs did not significantly affect the general development of zebrafish embryos, such as the body length or spontaneous tail-wagging movement. However, the hatching rate was reduced by the gradient SMFs (p < 0.05), but not the homogenous 22.0 T SMF. Moreover, although the zebrafish larva activities were differentially affected by these ultra-high SMFs (p < 0.05), the expression of several visual and neurodevelopmental genes (p < 0.05) was generally downregulated in the eyeball. Our findings suggest that exposure to ultra-high SMFs, especially the gradient SMFs, may have adverse effects on embryonic development, which should cause some attention to the future application of ultra-high field MRIs. As technology advances, it is conceivable that very strong magnetic fields may be adapted for use in medical imaging. Possible dangers associated with these higher Tesla fields need to be considered and evaluated prior to human use. Ultra-High static magnetic field may affect early embryonic development. High strength gradient static magnetic field exposure impacted zebrafish embryonic development. The application of very strong magnetic fields for MR technologies needs to be carefully evaluated.