Magnetic Structure Research Articles

Design and research of direct drive permanent magnet wind turbine based on Motor-CAD

Abstract The generator plays a crucial role in the wind power system, demanding characteristics such as exceptional efficiency, high reliability, high power density, operational stability, and corrosion resistance. Taking into account the performance demands of the wind turbine and the structural attributes of the permanent magnet synchronous generator, the electromagnetic design and simulation of a 9.4 kW direct drive permanent magnet wind turbine has been accomplished utilizing Motor-CAD software. The fractional slot stator structure of 60 poles and 54 slots is adopted to achieve effective reduction in cogging torque and enhance the dynamic performance and reliability of the generator. Double layer concentrated windings are used to enhance the electrical performance of the generator and lower the production cost. A surface-inserted radial magnetic circuit structure serves to increase the power density and dynamic performance of the generator and reduce the magnetic flux leakage coefficient. The prototype exhibits superiority in terms of its high efficiency, small footprint, and swift dynamic response. According to the simulation results, the prototype’s design parameters fully satisfy the specified design requirements for the wind turbine.

Multipolar Electromagnetic Emission of Newborn Magnetars

It is generally recognized that the electromagnetic multipolar emission from magnetars can be used to explain radiation from soft gamma repeaters or anomalous X-ray pulsars, but they have little impact on the spin-down of magnetars. We here present an analytical solution for the neutron star multipolar electromagnetic fields and their associated expected luminosities. We find that for newborn millisecond magnetars, the spin-down luminosity from higher multipolar components can match or even exceed that from the dipole component. Such high-intensity radiation will undoubtedly affect related astrophysical phenomena at the birth of a magnetar. We show that the spin-down luminosity from multipoles can well explain the majority of gamma-ray burst (GRB) afterglows, from the plateau starting at several hundred seconds until the normal decay phase lasting for many years. The fitted magnetar parameters for GRB afterglows are all typical values, with spins in the millisecond range and magnetic field strengths on the order of 1014–1015 G. Our results, in turn, provide support for the hypothesis that GRBs originate from the birth of magnetars with a period of a few milliseconds, thus deepening our understanding of the complex magnetic field structure and the equation of state of magnetars.

Fast Downflows Observed during a Polar Crown Filament Eruption

Solar filaments can undergo eruptions that result in the formation of coronal mass ejections, which can significantly impact planetary space environments. Observations of eruptions involving polar crown filaments, situated in the polar regions of the Sun, are limited. In this study, we report a polar crown filament eruption (SOL2023-06-12), characterized by fast downflows below the filament. The downflows appear instantly after the onset of the filament eruption and persist for approximately 2 hr, exhibiting plane-of-sky velocities ranging between 92 and 144 km s−1. They originate from the leading edge of the filament, and no clear acceleration is observed. Intriguingly, these downflows appear at two distinct sites, symmetrically positioned at the opposite ends of the conjugate flare ribbons. Based on the observations, we propose that the filament might be supported by a magnetic flux rope (MFR), and these downflows possibly occur along the legs of the MFR. The downflows likely result from continuous reconnections between the MFR and the overlying magnetic field structures and could either be reconnection outflows or redirected filament materials. We also observed horizontal drifting of the locations of downflows, which might correspond to the MFR’s footpoint drifting. This type of downflow can potentially be utilized to track the footpoints of MFRs during eruptions.

Simulation analysis and hydrodynamic performance optimization of small MHD thruster based on improved I-bridge structure

Abstract Magnetic hydrodynamic drive (MHD) generates thrust by the coupling interaction of three fields: flow field-electric field-magnetic field. Because this propulsion method has no propeller or mechanical structure, it has the advantages of quiet, simple structure, easy operation, flexible layout, and difficult to detect. This is the current research hot spot. In order to meet the needs of miniaturized silent propulsion, this paper selects a linear internal magnetic thruster for research and analysis and improves the design of an I-shaped magnetic bridge structure. Firstly, the thrust and efficiency of the thruster under ideal conditions are calculated, and the thruster model is established. The conclusion is that the I-shaped magnetic bridge can increase the magnetic field intensity of the channel and significantly improve the MHD propulsion efficiency. At the same time, it is found that MHD thruster can reduce noise during operation, but the current required for propulsion is large, and seawater electrolysis will occur, which has a certain impact on the environment. Finally, the problems of small direct drive MHD propulsion are analyzed, and the future development direction of MHD propulsion is prospected.

Nonlinear Coupling of Kinetic Alfvén Waves and Ion Acoustic Waves in the Inner Heliosphere

We study the nonlinear coupling of kinetic Alfvén waves with ion acoustic waves applicable to the Earth’s radiation belt and near-Sun streamer belt solar wind using dynamical equations in the form of modified Zakharov systems. Numerical simulations show the formation of magnetic field filamentary structures associated with density humps and dips which become turbulent at later times, redistributing the energy to higher wavenumbers. The magnetic power spectra exhibit an inertial range Kolmogorov-like spectral index value of −5/3 for k ⊥ ρ i < 1, followed by a steeper dissipation range spectra with indices ∼ −3 for the radiation belt case and ∼ −4 for the near-Sun streamer belt solar wind case, here k ⊥ and ρ i represent the wavevector component perpendicular to the background magnetic field and the ion thermal gyroradius, respectively. Applying quasilinear theory in terms of the Fokker–Planck equation in the region of wavenumber turbulent spectra, we find the particle distribution function flattening in the superthermal tail population which is the signature of particle energization and plasma heating.

Variations in the Inferred Cosmic-Ray Spectral Index as Measured by Neutron Monitors in Antarctica

A technique has recently been developed for tracking short-term spectral variations in Galactic cosmic rays (GCRs) using data from a single neutron monitor (NM), by collecting histograms of the time delay between successive neutron counts and extracting the leader fraction L as a proxy of the spectral index. Here we analyze L from four Antarctic NMs from 2015 March to 2023 September. We have calibrated L from the South Pole NM with respect to a daily spectral index determined from published data of GCR proton fluxes during 2015–2019 from the Alpha Magnetic Spectrometer (AMS-02) on board the International Space Station. Our results demonstrate a robust correlation between the leader fraction and the spectral index fit over the rigidity range 2.97–16.6 GV for AMS-02 data, with uncertainty of 0.018 in the daily spectral index as inferred from L. In addition to the 11 yr solar activity cycle, a wavelet analysis confirms a 27 day periodicity in the GCR flux and spectral index corresponding to solar rotation, especially near sunspot minimum, while the flux occasionally exhibits a strong harmonic at 13.5 days. The magnetic field component along a nominal Parker spiral (i.e., the magnetic sector structure) is a strong determinant of such spectral and flux variations, with the solar wind speed exerting an additional, nearly rigidity-independent influence on flux variations. Our investigation affirms the capability of ground-based NM stations to accurately and continuously monitor cosmic-ray spectral variations over the long-term future.

A fast-filament eruption observed in the Hα spectral line

Context. Solar filament eruptions usually appear to occur in association with the sudden explosive release of magnetic energy accumulated in long-lived arched magnetic structures. The released energy occasionally drives fast-filament eruptions that can be the source regions of coronal mass ejections. A quantitative analysis of high-speed filament eruptions is thus essential to help elucidate the formation and early acceleration of coronal mass ejections. Aims. The goal of this paper is to investigate the dynamic processes of a fast-filament eruption by using unprecedented high-resolution full-disk Hα imaging spectroscopy observations. Methods. The whole process of the eruption was captured in a wide spectral window of the Hα line (±9.0 Å), which allowed for the detection of highly Doppler-shifted plasma. By applying the “cloud model” and obtaining two-dimensional optical thickness spectra, we derived the Doppler velocity; the true eruption profiles (height, velocity, and acceleration); and the trajectory of the filament eruption in 3D space. Results. The Doppler velocity maps show that the filament was predominantly blueshifted. During the main and final process of the eruption, strongly blueshifted materials manifest, traveling with velocities exceeding 250 km s−1. The spectral analysis further revealed that the erupting filament is made of multiple components, some of which were Doppler-shifted approximately to −300 km s−1. We found that the filament eruption attains a maximum true velocity and acceleration of about 600 km s−1 and 2.5 km s−2, respectively, and its propagation direction deviates from the radial direction. On the other hand, downflows manifested as redshifted plasma close to the footpoints of the erupting filament move with velocities of 45–125 km s−1. We interpret these redshifted signatures as draining material and therefore as mass loss of the filament, which has implications for the dynamic and the acceleration process of the eruption. Furthermore, we have estimated the total mass of the Hα filament, resulting in ∼5.4 × 1015 g.

An All-in-One Magnetic Structure for Entire ZVS Range Auxiliary Power Module in Electrical Vehicles

An All-in-One Magnetic Structure for Entire ZVS Range Auxiliary Power Module in Electrical Vehicles

Can we rely on EUV emission to identify coronal waveguides?

Context. Traditional models of coronal oscillations rely on a modelling of the coronal structures that support them as compact cylindrical waveguides. An alternative model of the structure of the corona has recently been proposed, in which the thin strand-like coronal loops, that are observed in the extreme-UV (EUV) emission are the result of the line-of-sight integration of warps in more complex coronal structures. This is referred to as the coronal veil model. Aims. We extend the implications of the coronal veil model of the solar corona to models of coronal oscillations. Methods. Using convection-zone-to-corona simulations with the radiation-magnetohydrodynamics (rMHD) code Bifrost, we analysed the structure of the self-consistently formed simulated corona. We focused on the spatial variability of the volumetric emissivity of the Fe IX 171.073 Å EUV line and on the variability of the Alfvén speed, which captures the density and magnetic structuring of the simulated corona. We traced features associated with large magnitudes of the Alfvén speed gradient, which trap MHD waves and act as coronal waveguides. We searched for the correspondence with emitting regions, which appear as strand-like loops in the line-of-sight-integrated EUV emission. Results. We find that the cross sections of the waveguides bounded by large Alfvén speed gradients become less circular and more distorted with increasing height in the solar atmosphere. The waveguide filling factors corresponding to the fraction of the waveguides filled with plasma that emits in the given EUV wavelength range from 0.09–0.44. This suggests that we can only observe a small fraction of the waveguide. Similarly, the projected waveguide widths in the plane of the sky are several times larger than the widths of the apparent loops that are observed in the EUV. Conclusions. We conclude that the coronal veil structure is independent of the model. As a result, we find a lack of straightforward correspondence between peaks in the integrated emission profile that constitute apparent coronal loops and regions of plasma bound by a large Alfvén speed gradient that act as waveguides. Coronal waveguides cannot be reliably identified based on emission in a single EUV wavelength is not reliable in the simulated corona formed in convection-zone-to-corona models.

Properties of Solar Wind Current Sheets in the Martian Space Environment

Transient current sheets (CSs) are common magnetic structures in the solar wind that can significantly disturb the planetary space environment and cause space weather phenomena. This study focuses on their properties in the Martian space environment and investigates their transformations caused by the Martian bow shock. Based on 14 months of data from the Mars Atmosphere and Volatile Evolution mission during similar solar activity, 786 CSs with directional changes greater than 90° and magnetic field depression were automatically identified, including 256 events in the upstream solar wind and 530 events in the Martian magnetosheath. After crossing the bow shock, the duration and thickness of the CSs decrease, while their current density and occurrence rate significantly increase. In the Martian magnetosheath, CSs located on the dayside exhibit stronger current density, a relatively lower occurrence rate, and a smaller Bx/BT than CSs located on the nightside. From the dayside to the nightside, the predominant magnetic field component of CSs changes to Bx due to the draping process. Moreover, a clear dawn–dusk asymmetry in CS properties emerges from the foreshock to the downstream region of the Martian bow shock. Our results reveal the properties and evolution of solar wind CSs in the Martian space environment.

Magnetic Anisotropy Dominates over Physical and Magnetic Structure in Performance of Magnetic Nanoflowers

Magnetic nanoparticles are indispensable in many biomedical applications, but it remains unclear how the composition and structure will influence the application specific performance. We consider two compositions, ferrite and cobalt ferrite, synthesized under conditions that create aggregated multi‐core nanoparticles, called nanoflowers. Each nanoflower has an ionic surfactant or dextran to provide colloid stability in water. The composition, but not the coating, greatly impacts the heating output and the magnetic particle imaging tracer quality (with cobalt ferrite significantly reduced compared to ferrite). The cobalt ferrite nanoflowers have a core/shell structure with a reduced magnetization, which limits the effective magnetic anisotropy of the individual cobalt ferrite nanoflowers as well as the magnetic interactions among the nanoflowers. Both limitations significantly reduce the overall increase in the magnetic anisotropy with increasing magnetic field and consequently the nanoflowers’ efficacy for heating and imaging. Despite this, the formation of denser‐packed clusters and chains with external magnetic field in the ionic surfactant‐cobalt ferrite nanoflowers overcomes some of the shell's detrimental effects, resulting in better heating and imaging properties compared to the dextran‐cobalt ferrite. In short, the magnetic anisotropy dominates over physical and magnetic structure in the performance of the studied nanoflowers for heating and imaging applications.

The magnetic structure and spin-reorientation of ErGa.

The magnetic structure of the intermetallic compound ErGa has been determined using high-resolution neutron powder diffraction. This compound crystallizes in the orthorhombic (Cmcm, No. 63) CrB-type structure and orders ferromagnetically at 32 (2) K, with the Er moments initially aligned along the b axis. Upon cooling below 16 K, the Er magnetic moments cant away from the b axis towards the c axis. At 3 K, the Er moment is 8.7 (3) μB and the Er magnetic moments point in the direction 31 (3)° away from the crystallographic b axis, within the bc plane. 166Er Mössbauer spectroscopy work supports this structure and shows clear signals of the spin-reorientation in both the magnetic and electric quadrupole hyperfine interactions.

Magnetic properties and helical spin structure of another compound Ca3SbFe3Si2O14 from the family of iron-containing langasites

A strong interest is attracted to the langasite-type compounds containing magnetic 3d ions. Coexistence of electric and magnetic order parameters in such materials can provide a new variety of multiferroics. In our work, another Fe-based langasite with a nearly stoichiometric composition Ca3SbFe3Si2O14 was synthesized. X-ray diffraction and X-ray fluorescence analyses, studies of magnetic susceptibility, specific heat and Mössbauer spectroscopy were performed. The crystal structure of Ca3SbFe3Si2O14 (CSFS) was found to be hexagonal, space group P321. From full-profile analysis by the Le Bail method, the lattice parameters a = 8.115(1) Å, c = 5.058(1) Å, V = 288.4(1) Å3 were determined. The temperature dependence of magnetic susceptibility χ(Т) indicates the formation of long-range magnetic order at temperatures below TN = 34 K. The negative value of Weiss temperature θCW indicates the domination of antiferromagnetic exchange interaction. From the value of the Curie constant, the effective magnetic moment per Fe3+ ion µeff = 6.12 µB was estimated, which is slightly higher than the expected value 5.9 µB for the 3d5 - S = 5/2 state of iron. Measurements of the specific heat allowed a Debye temperature value ΘD = 390(10) K to be obtained. Based on the assessment of the magnetic contribution to the specific heat, the value of magnetic entropy ΔSmag ∼ 47.8 ± 5.6 J/mol K was determined. Hyperfine interaction parameters obtained from Mössbauer spectra indicate a helical magnetic ordering of iron moments in langasite Ca3SbFe3Si2O14. The period of a magnetic helicoid is about five periods of the crystal structure along the c axis. The calculated value of the angle (α) between the main axis of the electric field gradient Z′ at iron nuclei and the crystallographic c axis (67.2°) is significantly greater than in other langasites Ba3SbFe3Si2O14 (28.8°), Ba3NbFe3Si2O14 (36°), Ba3TaFe3Si2O14 (34.8°). This may be due to the more contracted FeO4 tetrahedra in CSFS compared to those in the other compositions.

Spontaneous reversal of spin chirality and competing phases in the topological magnet EuAl4

AbstractMaterials exhibiting a spontaneous reversal of spin chirality have the potential to drive the widespread adoption of chiral magnets in spintronic devices. Unlike the majority of chiral magnets that require the application of an external field to reverse the spin chirality, we observe the spin chirality to spontaneously reverse in the topological magnet EuAl4. Using resonant elastic x-ray scattering we demonstrate that all four magnetic phases in EuAl4 are single-k, where the first two magnetic phases are characterized by spin density wave order and the last two by helical spin order. A single spin chirality was stabilised across the 1mm2 sample, and the reversal of spin chirality occurred whilst maintaining a helical magnetic structure. At the onset of the helical magnetism, the crystal symmetry lowers to a chiral monoclinic space group, explaining the asymmetry in the chiral spin order, and establishing a mechanism by which the spin chirality could reverse via magnetostructural coupling.

Effects of Magnetostatic Interactions in FeNi-Based Multilayered Magnetoimpedance Elements.

Multilayered [Cu(3 nm)/FeNi(100 nm)]5/Cu(150 nm)/FeNi(10 nm)/Cu(150 nm)/FeNi(10 nm)/Cu(150 nm)/[Cu(3 nm)/FeNi(100 nm)]5 structures were obtained by using the magnetron sputtering technique in the external in-plane magnetic field. From these, multilayer magnetoimpedance elements were fabricated in the shape of elongated stripes using the lift-off lithographic process. In order to obtain maximum magnetoimpedance (MI) sensitivity with respect to the external magnetic field, the short side of the rectangular element was oriented along the direction of the technological magnetic field applied during the multilayered structure deposition. MI sensitivity was defined as the change of the total impedance or its real part per unit of the magnetic field. The design of the elements (multilayered structure, shape of the element, etc.) contributed to the dynamic and static magnetic properties. The magnetostatic properties of the MI elements, including analysis of the magnetic domain structure, indicated the crucial importance of magnetostatic interactions between FeNi magnetic layers in the analyzed [Cu(3 nm)/FeNi(100 nm)]5 multilayers. In addition, the uniformity of the magnetic parameters was defined by the advanced technique of the local measurements of the ferromagnetic resonance field. Dynamic methods allowed investigation of the elements at different thicknesses by varying the frequency of the electromagnetic excitation. The maximum sensitivity of 40%/Oe with respect to the applied field in the range of the fields of 3 Oe to 5 Oe is promising for different applications.

Effect of Zn-substitution on magnetic structure of cobalt ferrite nanoparticles.

This study investigates the effects of Zn substitution on the magnetic properties of ∼5nm cobalt ferrite nanoparticles (ZnxCo1-xFe2O4, where x = 0, 0.13, 0.34, and 0.55), demonstrating that Zn substitution induces complex changes in spin canting and prompts a redistribution of cations among the sublattices. We reconstructed the magnetic structure of these spinel ferrites by integrating the classical two-sublattice Néel model of ferrimagnetism with the data obtained from 57Fe Mössbauer spectrometry. Consequently, this research provides a comprehensive understanding of how Zn substitution tunes the magnetic properties of CoFe2O4 nanoparticles, offering valuable insights into the development of magnetic materials with tailored properties for various applications.

Understanding the Effects of Spacecraft Trajectories through Solar Coronal Mass Ejection Flux Ropes Using 3DCOREweb

This study investigates the impact of spacecraft positioning and trajectory on in situ signatures of coronal mass ejections (CMEs). Employing the 3DCORE model, a 3D flux rope model that can generate in situ profiles for any given point in space and time, we conduct forward modeling to analyze such signatures for various latitudinal and longitudinal positions, with respect to the flux rope apex, at 0.8 au. Using this approach, we explore the appearance of the resulting in situ profiles for different flux rope types, with different handedness and inclination angles, for both high- and low-twist CMEs. Our findings reveal that CMEs exhibit distinct differences in signatures between apex hits and flank encounters, with the latter displaying elongated profiles with reduced rotation. Notably, constant, nonrotating in situ signatures are only observed for flank encounters of low-twist CMEs, suggesting the existence of untwisted magnetic field lines within CME legs. Additionally, our study confirms the unambiguous appearance of different flux rope types in in situ signatures in all of the cases, barring some indistinguishable cases, contributing to the broader understanding and interpretation of observational data. Given the model assumptions, this may refute trajectory effects as the cause for mismatching flux rope types as identified in solar signatures. While acknowledging limitations inherent in our model, such as the assumption of constant twist and a nondeformable torus-like shape, we still draw relevant conclusions within the context of the global magnetic field structures of CMEs and the potential for distinguishing flux rope types based on in situ observations.

Electromagnetic modeling and analysis based on multilayer domain structure for GMI behavior in high frequency

Existing theoretical models on the frequency dependence of the magnetoimpedance (MI) in ferromagnetic microwires primarily describe the MI phenomenon at the limiting cases of lower MHz (<several hundred MHz) or higher GHz (>several GHz) ranges. However, in the intermediate region between these two ranges, known as the transition region, MI curves undergo complex transformations. These transformations have been documented in the literature, but their underlying causes remain poorly understood. Unambiguous knowledge of the domain structure and its correlation with MI properties is essential for elucidating this behavior. In this study, we have, for the first time, observed the inner core magnetic structure of Co-based microwires and revealed its relationship with the high-frequency MI effect. A distinct magnetic structure comprising longitudinal domains in the inner core (IC), circular domains in the outer shell (OS), and a transition region (TR) has been identified. This structure originates from compositional gradients and residual stresses during microwire fabrication. The IC/TR/OS structure manifests in the complex transformations of the MI behavior, exhibiting a turning point at GHz frequencies before the characteristic double MI peak. We developed a multilayer planar model that considers this more realistic magnetic structure, including the TR layer. This model successfully reproduces the key features of the MI curves and provides deeper insights into the high-frequency MI phenomenon. Our findings pave the way for optimizing the sensing capabilities of Co-based ferromagnetic microwires and demonstrate the potential of using high-frequency MI measurements to map their magnetic microstructures.

Cross-sectional surface analysis of magnetic domains, microstructures, and magnetic properties of the low-temperature phase MnBi prepared by low-temperature vacuum sintering

In this work, the low-temperature phase MnBi prepared by a low-temperature vacuum sintering process at 325 °C was studied. We found a significant increase in the energy product from 2.63 MGOe in the 12-h sintered sample to 3.64 MGOe in the 48-h sintered sample. This improvement is attributed to the solid-liquid diffusion process. Cross-sectional scanning electron microscopy (SEM) reveals that MnBi forms at the external surface of Mn particles and along interior surfaces, notably within cracks. Transmission electron microscopy further demonstrates that the Mn ratio increases and Bi decreases with distance from the crack. The selected area diffraction showed variations in the Mn ratio with distance from cracks and identified both Bi and MnBi phases in the MnBi layer. Magnetic force microscopy (MFM) analysis exhibited large phase shifts indicating repulsive or attractive forces in single ferromagnetic domains. This provides valuable insight into magnetic domains in the MnBi regions near Mn cracks. The MnBi formation model, developed for the vicinity of single cracks with uniform MnBi content, partly explains the magnetic interactions and phase shifts observed near these cracks. These findings provide significant insights into the MnBi microstructural and magnetic properties, potentially useful in tailoring and engineering magnetic structures.

Spiral Annealing of Magnetic Microwires.

A preprocessing technique named "spiral annealing" was applied for the first time to magnetic microwires. In this process, the sample was arranged in a flat spiral shape during annealing, and subsequent measurements were conducted on the unbent sample with the induced stress distribution along and transverse to the sample. The research utilized both magnetic and magneto-optical methods. The anisotropy field magnitude in both the volume and surface of the microwire was measured, and for the first time, a direct correlation between the anisotropy field and the curvature of a spirally annealed microwire was established. Additionally, a connection between the type of surface domain structure and the degree of spiral curvature was identified. The preservation of the distribution of spiral annealing-induced magnetic properties both along and across the microwire is a key effect influencing the technological application of the microwire. The range of induced curvature within which a specific helical magnetic structure can exist was also determined. This insight links the conditions of spiral annealing to the selection of microwires as active elements in magnetic sensors.