Magnetic Multipole Research Articles

Nonrelativistic ferromagnetotriakontadipolar order and spin splitting in hematite

We show that hematite, α−Fe2O3, below its Morin transition, has a ferroic ordering of rank-5 magnetic triakontadipoles on the Fe ions. In the absence of spin-orbit coupling, these are the lowest-order ferroically aligned magnetic multipoles, and they give rise to the g-wave nonrelativistic spin splitting in hematite. We find that the ferroically ordered magnetic triakontadipoles result from the simultaneous antiferroic ordering of the charge hexadecapoles and the magnetic dipoles, providing a route to manipulating the magnitude and the sign of the magnetic triakontadipoles as well as the spin splitting. Furthermore, we find that both the ferroic ordering of the magnetic triakontadipoles and many of the spin-split features persist in the weak ferromagnetic phase above the Morin transition temperature. Published by the American Physical Society 2024

Permanent Magnet Quadrupole for the Final Focus

The paper presents the general theory of permanent multipole magnets and describes the design of a Halbach-2 type quadrupole magnet as a final focus lens for colliders and similar projects. Optimal positions of permanent magnet segments and conditions for quadrupole field generation are investigated. Characteristics of the quadrupole such as aperture, gradient, gradient integral, length and number of segments are given. The results of measurements and calculations as well as the possibilities for gradient adjustment are discussed.

Selective Control of Electric Charge of Weyl Fermions in Pyrochlore Iridates.

Weyl fermions can exhibit exotic phenomena due to their magnetic charge in momentum space, while Weyl nodes are usually located away from Fermi energy, which forms electron or hole pockets as the electric charges. Previous studies have mostly focused on the magnetic charge, however, the electric charges are rarely explored. Here, the intriguing Hall responses arising from the interplay between magnetic and electric charges of Weyl fermions in pyrochlore iridates are reported. Explicitly, unexpected linear scaling is observed between the anomalous Hall conductivity and Hall carrier density in strained Nd2Ir2O7 thin films, and its slope shows a sign change approaching the Néel temperature of Nd. Theoretical calculations unveil that the cluster magnetic multipoles induce local energy inversion of Weyl nodes, which alters the electric charge of Weyl fermions and accounts for the observed nontrivial Hall responses. Moreover, the correlation between the magnetic and electric charges is further probed by voltage-controlled hydrogenation, which leads to the suppression of the anomalous Hall effect through electron filling. This work not only reveals the essential role of the both magnetic and electric charges of Weyl fermions, but also demonstrates the hydrogenation as an effective tuning knob in exploring correlated topological properties.

Retraction Note: Comparison between Discrete Magnetic Coils and Multipole Coils for Measurement of Plasma Displacement in IR-T1 Tokamak

Retraction Note: Comparison between Discrete Magnetic Coils and Multipole Coils for Measurement of Plasma Displacement in IR-T1 Tokamak

Mie-resonant metaphotonics

Mie-resonant metaphotonics is a rapidly developing field that employs the physics of Mie resonances to control light at the nanoscale. Mie resonances are excited in high-refractive-index transparent nanoparticles and voids created in dielectric media, and they can be used to achieve a wide range of optical effects, including enhanced light–matter interaction, nonlinear optical effects, and topological photonics. Here, we review the recent advances in Mie-resonant metaphotonics, with a focus on the physics of Mie resonances and their applications in metaphotonics and metasurfaces. Through a comprehensive multipolar analysis, we demonstrate the complex interplay of electric and magnetic multipoles that govern their interaction with light. Recent advances have unveiled a diverse spectrum of scattering phenomena that can be achieved within precisely engineered structures. Within this framework, we review the underlying mechanics of the first and second Kerker conditions and describe the intricate mechanisms guiding these nanostructures’ light-scattering properties. Moreover, we cover intriguing phenomena such as the anapole and bound or quasi-bound states in the continuum. Of profound interest are the numerous practical applications that result from these revelations. Ultrafast processes, the emergence of nanolasers, and advancements in magneto-optic devices represent just a fraction of the transformative applications.

Development of Precision Controllable Magnetic Field-Assisted Platform for Micro Electrical Machining.

In order to introduce the magnetic field into micro electrical machining technology to explore the influence of magnetic field on micro electrical machining, the development of a precision controllable magnetic field-assisted platform is particularly important. This platform needs to precisely control the spatial magnetic field. This study first completes the hardware design and construction of the magnetic field generation device, using electromagnetic coils with soft iron cores as the sources of the magnetic field. Mathematical models of the magnetic field are established and calibrated. Since the magnetic dipole model cannot effectively describe the magnetic field generated by the electromagnetic coil, this study adopts a more precise description method: the spherical harmonic function expansion model and the magnetic multipole superposition model. The calibration of the magnetic field model is based on actual excitation magnetic field data, so a magnetic field sampling device is designed to obtain the excitation magnetic field of the workspace. The model is calibrated based on a combination of the theoretical model and magnetic field data, and the performance of the constructed setup is analyzed. Finally, a magnetic field-assisted platform has been developed which can generate magnetic fields in any direction within the workspace with intensities ranging from 0 to 0.2 T. Its magnetic field model arrives at an error percentage of 2.986%, a variance of 0.9977, and a root mean square error (RMSE) of 0.71 mT, achieving precise control of the magnetic field in the workspace.

Development of HFRS Superconducting Multipole Magnets for HIAF

Development of HFRS Superconducting Multipole Magnets for HIAF

Status of Multipole Magnets for Hefei Advanced Light Facility

Status of Multipole Magnets for Hefei Advanced Light Facility

Spin-Polarization Control of Photoelectrons Using Poincaré Fields.

Efficient helicity transfer from Poincaré fields to electrons of hydrogenic ions is revealed for the first time by four-dimensional relativistic simulations. The magnetic multipole class of Poincaré fields is chosen due to its fundamental role in light-matter spin coupling, and the calculation is demonstrated for Ne^{9+} ion irradiated by single and multimode x-ray pulses. Photoelectrons of both helicities emerge synchronously from the ion ensemble, and their directionality is controllable through the radiation mode numbers. The helicity density distributions display novel structures composed of jets, spirals, and rings, among others, that are unique to the combination of atomic and field parameters. Our approach to generate spin-polarized leptons using Poincaré fields may provide a new platform for helicity characterization based on advanced numerical capabilities.

Multi-pole ratio single-winding pole-changing permanent magnet motor design and analysis

Multi-pole ratio single-winding pole-changing permanent magnet motor design and analysis

The Influence of the Design and Technological Parameters of Polymer-Based Multipolar Magnets with SrFeO Hard Magnetic Filler on the Residual Magnetic Properties

The Influence of the Design and Technological Parameters of Polymer-Based Multipolar Magnets with SrFeO Hard Magnetic Filler on the Residual Magnetic Properties

Effect of external fields and currents on electronic nematic ordering with quadrupole moments

We theoretically investigate the effect of external fields and currents on electronic nematic orderings based on the concept of augmented multipoles consisting of electric, magnetic, magnetic toroidal, and electric toroidal multipoles. We show the relation between rank-2 electric quadrupoles and the other multipoles, the former of which corresponds to the microscopic order parameter for the nematic phases. The electric (magnetic) field induces the rank-1 and rank-3 electric (magnetic) multipoles and rank-2 electric toroidal (magnetic toroidal) quadrupoles, while the electric current induces the rank-1 and rank-3 magnetic toroidal multipoles and rank-2 magnetic quadrupoles. We classify the active multipoles under magnetic point groups, which will be a reference to explore cross-correlation and transport phenomena in nematic phases. As a demonstration, we show that unconventional symmetric and antisymmetric spin splittings are brought about by field-induced toroidal multipoles.

Characterization of Magnetorheological Impact Foams in Compression.

This study focuses on the development and compressive characteristics of magnetorheological elastomeric foam (MREF) as an adaptive cushioning material designed to protect payloads from a broader spectrum of impact loads. The MREF exhibits softness and flexibility under light compressive loads and low strains, yet it becomes rigid in response to higher impact loads and elevated strains. The synthesis of MREF involved suspending micron-sized carbonyl Fe particles in an uncured silicone elastomeric foam. A catalyzed addition crosslinking reaction, facilitated by platinum compounds, was employed to create the rapidly setting silicone foam at room temperature, simplifying the synthesis process. Isotropic MREF samples with varying Fe particle volume fractions (0%, 2.5%, 5%, 7.5%, and 10%) were prepared to assess the effect of particle concentrations. Quasi-static and dynamic compressive stress tests on the MREF samples placed between two multipole flexible strip magnets were conducted using an Instron servo-hydraulic test machine. The tests provided measurements of magnetic field-sensitive compressive properties, including compression stress, energy absorption capability, complex modulus, and equivalent viscous damping. Furthermore, the experimental investigation also explored the influence of magnet placement directions (0° and 90°) on the compressive properties of the MREFs.

Surface Magnetization in Antiferromagnets: Classification, Example Materials, and Relation to Magnetoelectric Responses

We use symmetry analysis and density-functional theory to determine and characterize surface terminations that have a finite equilibrium magnetization density in antiferromagnetic materials. A nonzero magnetic dipole moment per unit area or “surface magnetization” can arise on particular surfaces of many antiferromagnets due to the bulk magnetic symmetries. Such surface magnetization underlies intriguing physical phenomena like interfacial magnetic coupling and can be used as a readout method of antiferromagnetic domains. However, a universal description of antiferromagnetic surface magnetization is lacking. We first introduce a classification system based on whether the surface magnetization is either sensitive or robust to roughness and on whether the magnetic dipoles at surface of interest are compensated or uncompensated when the bulk magnetic order is retained at the surface. We show that roughness-sensitive categories can be identified by a simple extension of a previously established group-theory formalism for identifying roughness-robust surface magnetization. We then map the group-theory method of identifying surface magnetization to a novel description in terms of bulk magnetic multipoles, which are already established as symmetry indicators for bulk magnetoelectric responses at both linear and higher orders. We use density-functional calculations to illustrate that nominally compensated surfaces in magnetoelectric Cr2O3 and centrosymmetric altermagnetic FeF2 develop a finite magnetization density at the surface, in agreement with our predictions based on both group theory and the ordering of the bulk multipoles. Our analysis provides a comprehensive basis for understanding the surface magnetic properties and their intimate correspondence to bulk magnetoelectric effects in antiferromagnets and has important implications for technologically relevant phenomena such as exchange-bias coupling. Published by the American Physical Society 2024

Magnetic transverse unidirectional scattering and longitudinal displacement sensing in silicon nanodimer

Unidirectional scattering, crucial for manipulating light at the nanoscale, has wide-ranging applications from optical manipulation to sensing. While traditionally achieved through interactions between electric multipoles or between electric and magnetic multipoles, reports on unidirectional scattering driven purely by magnetic multipoles are limited. In this study, we undertake a theoretical exploration of transverse unidirectional scattering induced by magnetic multipoles, employing tightly focused azimuthally polarized beams (APBs) in interaction with a silicon nanodimer comprising two non-concentric nanorings. Through numerical simulations and theoretical analysis, we validate the transverse unidirectional scattering, predominantly governed by magnetic dipolar and quadrupolar resonances. Moreover, the directionality of this unidirectional scattering shows a strong correlation with the longitudinal displacement of the nanodimer within a specific range, showcasing its potential for longitudinal displacement sensing. Our study advances optical scattering control in nanostructures and guides the design of on-chip longitudinal displacement sensors.

Surface magnetic flux density optimization considering effect of aligned magnetic field molding conditions of ring-shaped multi-pole anisotropic ferrite permanent magnet for DC motors

The ring-shaped anisotropic ferrite magnet with multiple poles boasts significant benefits for brushless DC motors (BDCMs). However, the prevalent production method involves dry magnetic field molding, making it challenging to enhance the magnetic properties. Herein, ferrite powder made from iron oxide, a by-product of the steel industry, is used as the starting material of magnets, and the differences between dry and wet molding approaches on the surface magnetic flux density of a ring-shaped multi-pole anisotropic ferrite magnet are first investigated. ANSYS MAXWELL conducted an initial simulation to achieve the design specifications of the wet molding mold. Following this, the mold was prepared for the fabrication of ring magnets. Compared to magnets prepared via dry molding, those produced through wet molding exhibit a peak surface magnetic flux density of approximately 15.9% higher, demonstrating significant potential for industrial applications and substantial enhancement of the key magnetic properties of wet molded ferrite ring magnets. To achieve increased surface flux density of ring magnets, it is common practice to utilize magnetic powders with greater magnetic properties when molding the magnets. However, this requires a costly mold redesign. In this study, higher surface magnetic flux densities can be achieved for ring magnets by simply adjusting the shape, size and magnetization direction of NdFeB permanent magnets that provide a constant aligned magnetic field in the mold without requiring any alterations to the existing mold's dimensions. The findings of this study could improve the effectiveness of existing motor designs. The usage of ring-shaped multi-pole anisotropic ferrite magnets is anticipated to witness a surge in the coming years, driven by the growth of energy-efficient motors in diverse sectors.

Electric Field Characteristics of Rotating Permanent Magnet Stimulation.

Neurostimulation devices that use rotating permanent magnets are being explored for their potential therapeutic benefits in patients with psychiatric and neurological disorders. This study aims to characterize the electric field (E-field) for ten configurations of rotating magnets using finite element analysis and phantom measurements. Various configurations were modeled, including single or multiple magnets, and bipolar or multipolar magnets, rotated at 10, 13.3, and 350 revolutions per second (rps). E-field strengths were also measured using a hollow sphere (r=9.2 cm) filled with a 0.9% sodium chloride solution and with a dipole probe. The E-field spatial distribution is determined by the magnets' dimensions, number of poles, direction of the magnetization, and axis of rotation, while the E-field strength is determined by the magnets' rotational frequency and magnetic field strength. The induced E-field strength on the surface of the head ranged between 0.0092 and 0.52 V/m. In the range of rotational frequencies applied, the induced E-field strengths were approximately an order or two of magnitude lower than those delivered by conventional transcranial magnetic stimulation. The impact of rotational frequency on E-field strength represents a confound in clinical trials that seek to tailor rotational frequency to individual neural oscillations. This factor could explain some of the variability observed in clinical trial outcomes.

Batch Fine Magnetic Pattern Transfer Method on Permanent Magnets Using Coercivity Change during Heating for Magnetic MEMS.

In magnetic microelectromechanical systems (MEMSs), permanent magnets in the form of a thick film or thin plate are used for structural and manufacturing purposes. However, the geometric shape induces a strong self-demagnetization field during thickness-direction magnetization, limiting the surface magnetic flux density and output power. The magnets must be segmented or magnetized in a fine and multi-pole manner to weaken the self-demagnetization field. Few studies have been performed on fine multi-pole magnetization techniques that can generate a higher surface magnetic flux density than segmented magnets and are suitable for mass production. This paper proposes a batch fine multi-pole magnetic pattern transfer (MPT) method for the magnets of MEMS devices. The proposed method uses two master magnets with identical magnetic patterns to sandwich a target magnet. Subsequently, the coercivity of the target magnet is reduced via heating, and the master magnet's magnetic pattern is transferred to the target magnet. Stripe, checkerboard, and concentric circle patterns with a pole pitch of 0.3 mm are magnetized on the NdFeB master magnets N38EH with high intrinsic coercivity via laser-assisted heating magnetization. The MPT yields the highest surface magnetic flux density at 160 °C, reaching 39.7-66.1% of the ideal magnetization pattern on the NdFeB target magnet N35.

Conceptual design of multipole injection kicker magnets for the ILSF storage ring

The standard injection scheme of the Iranian Light Source Facility(ILSF) is composed of 2 septum and 4 kicker magnets installed in a 7-meter-long straight section. Further tuning of the 4 kicker devices to reduce perturbations has proven to be almost impossible since it requires having 4 identical magnets, electronics and Ti-coated ceramic chambers. Different from pulsed dipole kicker magnets used in a conventional local-bump injection, a single nonlinear or multipole kicker provides a nonlinear distribution of magnetic fields, which has a maximum value off the axis where the injected beam arrives and a zero or near-zero value at the center where the stored beam passes by. So, here the designs of different multipole kickers, including sextupole, octupole and a nonlinear kicker, have been investigated and compared.

Global solar photospheric and coronal magnetic field over activity cycles 21–25

The evolution of the global solar magnetic field from the beginning of cycle 21 (mid-1970s) until the currently-ascending cycle 25 is described using photospheric full-disk and synoptic magnetograms from NSO Kitt Peak Vacuum Telescope (KPVT) 512-channel and Spectromagnetograph (SPMG) and the Synoptic Optical Long-term Investigation of the Sun (SOLIS) Vector Spectro-Magnetograph (VSM) and Global Oscillations Network Group (GONG), and Stanford University’s Wilcox Solar Observatory (WSO). The evolving strength and symmetry of the global coronal field are described by potential-field source-surface models decomposed into axisymmetric and non-axisymmetric, and even- and odd-ordered magnetic multipoles. The overall weakness of the global solar magnetic field since cycle 23 splits the 50-year observing window into the stronger, simpler, more hemispherically symmetric cycles 21 and 22 and the weaker, more complex cycles 23 and 24. An anomalously large decrease in the global solar field strength occurred during cycles 23, and an anomalously weak axial/polar field resulted from that cycle, accompanied by an anomalously weak radial interplanetary magnetic field (IMF) during cycle 23 activity minimum and a weakened radial IMF overall since cycle 23. The general long-term decline in solar field strength and the development during cycle 24 of strong swings of hemispheric and polar asymmetry are analyzed in detail, including their transfer through global coronal structural changes to dominate mean in situ interplanetary field measurements for several years. Although more symmetric than cycle 24, the rise phase of cycle 25 began with the southern leading the northern hemisphere, but the north has recovered to lead this cycle’s polar field reversal. The mean polar flux (poleward of ±60°) has reversed at each pole, so far more symmetrically than the cycle 23 and 24 polar reversals.