Magnetic Dipole Research Articles

Direct Chiral Discrimination with NMR.

Unaided nuclear magnetic resonance (NMR) spectroscopy is considered incapable of distinguishing enantiomers. However, as first derived by A.D. Buckingham, the tensor coupling the electric and magnetic dipoles is space-dependent, which varies according to the molecular structure, hence, would be different for two enantiomers. Exploiting the odd-parity coupling tensor, a new variant of a double-resonant radiofrequency (RF) NMR detector is developed, which is sensitive to both electric and magnetic dipoles. Using the detector, a new method for liquid-state NMR is developed and elaborated, with which two enantiomers are successfully discriminated.

Synthesis, Structural Features and Fluorescent Properties of Terbium Acylpyrazolone Complexes

AbstractThree 8‐coordinated terbium acylpyrazolone complexes [Tb(DMBPMP)3(H2O)2] (Tb1), [Tb(DMBMCPMP)3(H2O)2] (Tb2), and [Tb(DMBPTMP)3(H2O)2] (Tb3) with a distorted bicapped trigonal prismatic structure were synthesized (where, 3,5‐dimethylbenzoyl 1‐(phenyl = DMBPMP/m‐chlorophenyl = DMBMCPMP/p‐tolyl = DMBPTMP) 3‐methyl 5‐pyrazolone). The structures of the complexes were comprehensively analyzed using mass ESI, FTIR, UV–vis, powder XRD, and TG‐DTA methods. Single‐crystal analysis of Tb3·H2O confirmed an eight‐coordinate structure (TbO8) with a distorted bicapped trigonal prismatic geometry. In the on‐state emission spectrum, the 5D4 → 7F5 transition exhibits hypersensitivity in the green region of the visible spectrum (∼540–560 nm). The differences between electric dipole (ED) and magnetic dipole (MD) transitions indicate a small degree of asymmetry. The examination of solid‐state emission spectra included the assessment of intensity, G/B ratio, green color purity, and the antenna effect energy diagram.

On the low-energy electromagnetic dipole modes in 151,153,155Sm Nuclei

The recently observed low-energy magnetic dipole (M1) and electric dipole (E1) excitations in deformed 151,153,155Sm are theoretically analysed. Rotational Invariant (RI-) and Translational-Galilean Invariant (TGI-) Quasiparticle Nuclear Model (QPNM) are used in the calculation of M1 and E1 properties, respectively. Both theories consider monopole pairing between nucleons, and the deformed Woods-Saxon potential is used as the mean-field potential. Pyatov's symmetry restoration procedure is applied in these models to eliminate the spurious modes from the intrinsic nuclear excitations. Model calculations show that although E1 transitions dominate the low-energy dipole spectra of 151,153,155Sm, many low-lying M1 transitions exist in these nuclei. It is shown that the most significant contribution to E1 and M1 excitation comes from ΔK=±1 transitions. The theory satisfactorily reproduces the gross features of low-lying dipole modes determined from the Oslo Method analysis of the experimental spectra.

Current potential patches

A novel form of the current potential, a mathematical tool for the design of stellarators and stellarator coils, is developed. Specifically, these are current potentials with a finite-element basis, called current potential patches. Current potential patches leverage the relationship between distributions of magnetic dipoles and current potentials to explore limits of the access properties of stellarator coil sets. An example calculation is shown using the Helically Symmetric Experiment (HSX) equilibrium, demonstrating the method's use in coil design and understanding the limits of the access properties of coil sets. Current potential patches have additional desirable properties such as of promoting sparse current sheet solutions and identifying crucial locations of shaping current placement. A result is found for the HSX equilibrium that shaping currents covering only 22% of the winding surface are sufficient to produce the equilibrium to a good accuracy, provided a toroidal field is generated by an exterior coil set.

2D mechanical representation of superconducting magnets: A comparative study of plane stress and plane strain

When approaching the mechanical design of a superconducting magnet, whenever possible the starting model is a 2D approximation. If rotational symmetry (solenoid-like winding) is present, the 2D representation is unique and contains no approximations. If, on the other hand, a non-axisymmetric system is opted for, the 2D representation is not unique and there are main options available, as plane stress, plane stress with thickness, plane strain and generalized plane strain. Considering z as the direction normal to the 2D plane, the plane stress option defines a stress state in which no normal or shear stresses perpendicular to the xy plane can occur (σz=σxz=σyz=0). In this option, deformation can occur in the thickness direction of the element, which will become thinner when stretched and thicker when compressed; it is generally used for objects with limited depth (thin objects).In contrast, plane strain refers to the fact that deformation can only occur in plane, which means that no out-of-plane deformation will occur (ϵz=ϵxz=ϵyz=0). The plane strain option is generally appropriate for structures of nearly infinite length, relative to their cross section, that exhibit negligible length changes under load. The “generalized plane strain” option imposes the axial strain equal to a constant value; this condition does not reproduce the real operating condition of the magnet and is therefore excluded. The “plane stress with thickness” uses the same equations as the plane stress option but, output quantities are given per unit length defined with thickness; therefore, it is again excluded from the comparison. Superconducting magnets, such as dipoles, do not fit neatly into any of the above options: they are far from thin but deform longitudinally under load. This work reports a comparative study of plane stress and plane strain in the specific case study of a dipole magnet.

A Novel Modular Cascaded H-Bridge High-Power Accelerator Dipole Magnet Pulse Power Supply for HIRFL-CSRm

A Novel Modular Cascaded H-Bridge High-Power Accelerator Dipole Magnet Pulse Power Supply for HIRFL-CSRm

Modelling PM dipoles with longitudinal field gradient for SILA facility

Computational models are described which were built for parametric simulations of permanent magnet (PM) dipoles with a longitudinal field gradient. The dipoles will be used as bending magnets in the synchrotron facility SILA, a new project of the National Research Center “Kurchatov Institute”. The dipoles employ a Sm-Co permanent magnet material and pure iron. The need for high magnetic performance and anticipated interference between neighbouring components is a challenge for design and construction of the magnet system. For this reason the magnet designs must rely on precision 3D simulations. The dipoles are described in detail with parameterized models. Parametric simulations are to be applied at all stages of the project till the commissioning to provide realistic prediction of the magnet behaviour.

CORC® wires allowing bending to 20 mm radius with 97.5% retention in critical current and having an engineering current density of 530 A mm−2 at 20 T

Abstract Low-inductance, high-field insert solenoid magnets and 20 T dipole magnets for particle accelerators require flexible cables, wound from high-temperature superconductors (HTS) such as RE-Ba2Cu3O7-δ (REBCO) coated conductors, that allow bending to a 20 mm radius without significant degradation in performance. They require an operating current of at least 5 kA and a high engineering current density (Je) exceeding 500 A/mm2 at 20 T. HTS cable technologies that target such demanding magnet applications so far haven’t been able to meet the combination of these requirements.
Here we present the development of the next generation of Conductor on Round Core (CORC®) wires that improves their bending flexibility by factor of more than 2 compared to previous generation CORC® wires. CORC® wires now allow for a bending radius of 20 mm with only 2 – 3 % performance degradation. They allow bending to a radius of 15 mm with a performance retention of 83.5 %. The performance of 30-tape CORC® wires wound from 2 mm wide REBCO tapes from SuperPower Inc, SuperOx and Shanghai Superconductor Technologies was measured at magnetic fields up to 12 T. The overall performance at high magnetic fields of the next generation of CORC® wires improved by a factor of 1.5 – 1.8, depending on the REBCO tape manufacturer. CORC® wires wound from production REBCO tapes achieved a new record Je of 751 A/mm2 at a current of 8.3 kA at 12 T, and a Je of 530 A/mm2 at a current of 5.8 kA when extrapolated to 20 T. 

Efficient second-harmonic generation in a lithium niobate metasurface governed by high-Q magnetic toroidal dipole resonances.

Lithium niobate (LN) is an excellent nonlinear optical material due to its large nonlinear coefficient, low loss, and broad optical transparency window. So, it is widely used in the generation of nonlinear harmonics. Magnetic toroidal dipole (MTD) resonance is a special optical resonance mode, which can effectively localize the light field inside the device, thus enhancing the nonlinear effects of the materials. In this work, we numerically study the second-harmonic generation (SHG) effect of the LN metasurface based on the MTD mode with a high quality factor (Q-factor). The designed LN nanorod dimer metasurface supports high Q-factor MTD guided mode resonances (GMRs), which are excited by varying the center spacing of the two nanorods, and the Q-factor can be controlled by the offset distance. The excited MTD can effectively confine the electric field within the device, which enables the LN metasurface SHG conversion efficiency to reach 1.15 × 10-2. In addition, by adjusting the structural parameters, it is possible to effectively modulate the wavelength and conversion efficiency of the SHG. Our results provide a new route for high-quality nonlinear light sources.

Toroidal mode trapping in a magnetic meta-molecule

Abstract In this paper, we establish the relationship between the eigenmodes and the scattering characteristics of a meta-molecule made of magnetic disks from the point of view of the manifestation of its toroidal response. In particular, we examine the electric and magnetic dipole contributions to the scattering cross-sections obtained in the framework of the multipole decomposition method while accounting for the polarizability and magnetization induced in the structure by the field of incoming radiation. We find out that with increasing permeability, the toroidal mode is trapped in the meta-molecule due to the presence of its magnetization part, which may have a practical perspective in gyrotropy, permittivity, and permeability sensing.

Origins of Electromagnetic Radiation from Spintronic Terahertz Emitters: A Time-Dependent Density Functional Theory plus Jefimenko Equations Approach.

Microscopic origins of charge currents and electromagnetic (EM) radiation generated by them in spintronic THz emitters-such as, femtosecond laser pulse-driven single magnetic layer or its heterostructures with a nonmagnetic layer hosting strong spin-orbit coupling (SOC)-remain poorly understood despite nearly three decades since the discovery of ultrafast demagnetization. We introduce a first-principles method to compute these quantities, where the dynamics of charge and current densities is obtained from real-time time-dependent density functional theory, which are then fed into the Jefimenko equations for properly retarded electric and magnetic field solutions of the Maxwell equations. By Fourier transforming different time-dependent terms in the Jefimenko equations, we unravel that in the 0.1-30THz range the electric field of far-field EM radiation by the Ni layer, chosen as an example, is dominated by charge current pumped by demagnetization, while often invoked magnetic dipole radiation from the time-dependent magnetization of a single magnetic layer is a negligible effect. Such an effect of charge current pumping by a time-dependent quantum system, whose magnetization is shrinking while its vector does not rotate, does not require any spin-to-charge conversion via SOC effects. In the Ni/Pt bilayer, EM radiation remains dominated by the charge current within the Ni layer, whose magnitude is larger than in the case of a single Ni layer due to faster demagnetization, while often invoked spin-to-charge conversion within the Pt layer provides an additional but smaller contribution. By using the Poynting vector and its flux, we also quantify the efficiency of conversion of light into emitted EM radiation, and its angular distribution.

Hybrid Anapole Induced Chirality in Metasurfaces.

The interaction between light and matter, particularly chirality, plays a pivotal role in modern science and technology. Typically, metasurfaces achieve chiro-optical effects by coupling electric and magnetic dipoles in specific orientations. In this work, the design and optimization of an asymmetric H-shaped metasurface is explored to induce hybrid anapole (HA) for optical activity. When the symmetry of the metasurface structure is disrupted, the design can simultaneously excite first-order and pseudo high-order HA under illumination with a specific circular polarization, both occurring within the same spectral regime. This results in high reflection for one circular polarization and a significant reduction in reflection for the orthogonal polarization, thereby exhibiting exceptional chiro-optical activity. Moreover, the HA-based chiral metasurface demonstrates strong polarization control capabilities, as verified by Stokes parameter analysis, revealing high birefringence and a pronounced dependence on the incident polarization angle. These results provide valuable insights for the design and optimization of HA metasurfaces for advanced optical applications and polarization control, paving the way for new developments in chiral nanophotonics.

Lagrangian for Interacting Electric Charge and Magnetic Dipole. Derivation of Interaction Forces in Quantum Effects of the Aharonov-Bohm Type

Lagrangian for Interacting Electric Charge and Magnetic Dipole. Derivation of Interaction Forces in Quantum Effects of the Aharonov-Bohm Type

Mie Magnetic Structural Colors from Short Chains of TiO2 Nanospheres.

We demonstrate distinctive structural colors within a small footprint by using a short chain of nanospheres. Rather than using high-index materials like Si (n ∼ 4), which ensure strong modal confinement, TiO2 is employed. TiO2 has an intermediate index (n ∼ 2), promoting stronger modal coupling between the magnetic dipoles of each particle. This approach enables selective engineering of the magnetic response and yields larger spectral changes compared to that of Si. Despite the lower refractive index, the absence of absorption in TiO2 also produces higher scattering intensities than Si. We develop a quasistatic analytical model that describes the dipolar modal coupling in a trimer and use it to reveal distinct magnetic field strengths in the outer or central particle depending on the polarization of incident light. These results suggest pathways to manipulate the magnetic field in chains of particles and create vibrant structural colors with simple configurations.

Transverse magneto-optical Kerr effect enhancement in si–ni nanogratings by mie and surface lattice resonances

We demonstrate experimentally that a one-dimensional array of silicon nanowires periodically placed on a nickel substrate enhances the transverse magneto-optical Kerr effect (TMOKE) compared to a nickel film. The enhancement mechanism is associated with the excitation of two types of resonances: multipole Mie resonances in each nanowire and surface lattice resonances (SLRs) emerging from the periodic arrangement of the nanowires. The maximal TMOKE values reached up to 1.9 % and 2.6 % due to the excitation of SLR and a magnetic dipole resonance, respectively. When the SLR is excited, the spectral width of the TMOKE enhancement is narrower compared to the case of the magnetic dipole resonance.

Shielded Pair Method for Beam Screen Surface Resistance Measurement at Cryogenic Temperature

The shielded pair resonator method is a useful tool in the measurement of accelerator components, such as the beam screens used in the Large Hadron Collider (LHC), the High-Luminosity (HL) LHC, or future accelerators. It can measure the resistive losses at several frequency points by separating the resistive losses on the sample from other sources of losses. We built a new resonator to be inserted into a superconducting dipole magnet (peak magnetic field of 9.5 T) and to measure the surface resistance of beam screens, such as LHC beam screens coated with amorphous carbon (a-C). The device can measure surface resistance at any temperature between 4.2 K and 300 K, in the frequency range of 400 MHz to 1600 MHz. We conducted the first surface resistance measurements of two a-C coated beam screens at 4.2 K and showed that the 200 nm to 400 nm titanium underlayer plus 50 nm a-C only has a limited effect on the surface resistance. This first result supports the choice of this coating as baseline for the HL-LHC triplets magnets upgrade. The resonator will have an important role in the characterization of next-generation beam screens, such as a beam screen with laser-engineered surface structure (LESS). Further measurements of the LHC beam screen in the presence of magnetic fields up to 9.5 T and throughout the full temperature range are going to be reported separately.

Study of Noise Reduction and Identification of Internal Damage Signals in Wire Ropes

Mining wire rope, a frequently used load-bearing element, suffers various forms of damage over extended periods of operation. Damage occurring within the wire rope, which is not visible to the naked eye and is difficult to detect accurately with current technology, is of particular concern. Consequently, the identification of internal damage assumes paramount importance in ensuring mine safety. This study proposes a wire rope internal damage noise reduction and identification method, first of all, through a three-dimensional magnetic dipole model to achieve the detection and analysis of the internal damage of the wire rope. Simultaneously, a sensor system capable of accurately detecting the internal damage of wire rope is developed and validated through experimentation. A novel approach is proposed to address the noise reduction issue in the design process. This approach utilizes a particle swarm optimization variational modal decomposition method to enhance the signal-to-noise ratio. Additionally, a dual-attention mode, which combines channel attention and spatial attention, is integrated into the CNN-GRU network model. This network model is specifically designed for the detection of internal damage in steel wire ropes. The proposed method successfully achieves quantitative identification of internal damage in steel wire ropes. The experimental findings demonstrate that this approach is capable of efficiently detecting internal damage in wire rope and possesses the capacity to quantitatively identify such damage, enabling adaptive identification of wire rope.

Enhancing Circularly Polarized Luminescence Dissymmetry Factor of Chiral Cylindrical Molecules to -0.56 through Intramolecular Short-Range Charge Transfer.

High-performance circularly polarized luminescent (CPL) materials have received wide attention recently by virtue of broad application in circularly polarized light-emitting diodes, 3D display, and encryption. Reaching both high luminescence efficiency and strong luminescence dissymmetry factor (glum) is still a challenging goal that requires continuous efforts. Herein, we performed a systematic theoretical investigation on the chiroptical properties of helical cylindrical molecules (-)-[4]cyclo-2,6-anthracene [(-)-[4]CA2,6] and (P)-[4]cyclo-2,8-chrysenylene [(P)-[4]CC2,8], and found that the unique and symmetric cylindrical structure could make the transition dipole moment components offset along the cylindrical surface but concentrated along the vertical central axis. This structural superiority contributes the collinear electric and magnetic transition dipole moment vectors and thus the large glum. Based on the results of decomposed transition dipole moment vectors to individual atoms, an effective strategy to enhance the glum through introducing intramolecular short-range charge transfer by embedding B,N atoms is proposed. The decreased electric transition dipole moment and well-kept magnetic transition dipole moment enable the glum of B,N-embedded designed molecules (-)-[4]CA2,6-4BN and (P)-[4]CC2,8-4BN up to -0.31 and -0.56, respectively. This molecular-insight investigation deepens the understanding of the structure-property relationship and provides efficient guidance for improving glum of CPL materials.

Increasing the Magnetic Transition Dipole Moment of Chiral Perovskite Through Eu3+ Doping

AbstractChiral hybrid organic‐inorganic perovskites (HOIPs) are widely investigated due to their superior chiroptical and chiral spintronic properties. Research on the enhancement of chiroptical performance is highly important for the real application of chiral HOIPs. This work employed a rare earth doping strategy to increase the magnetic transition dipole moment of chiral 2D HOIPs R‐/S‐NPB (NPB = 1‐(1‐naphthyl) ethylammonium lead bromide). Doping with Eu3+ does not change the original layered NPB microstructure, and R‐/S‐NPB‐Eu exhibited the magnetic dipole‐allowed transition luminescence of Eu3+ at 594 nm (5D0→7F1). Circular polarized luminescence (CPL) spectra combined with theoretical calculations and transient photoluminescence measurements indicated that the introduction of Eu3+ can enhance the magnetic transition dipole moment of R‐/S‐NPB, thus resulting in an unprecedented glum of 0.05. To the best of our knowledge, this is the highest value for chiral perovskite films. This work combines the unique and superior optoelectronic properties of rare‐earth ions with chiral perovskite and develops an efficient strategy to increase its anisotropy factor, which can accelerate the development of chiral optoelectronics and spintronics towards real application.

Neutrino mass model and dark matter with Y = 0 inert triplet scalar

We study a one-loop induced neutrino mass model with an inert isospin triplet scalar field of Y=0 and heavier isospin doublet vector-like leptons and singlet Majorana right-handed fermions. In addition to the neutrino mass matrix, we explain sizable scale of muon anomalous magnetic dipole moment 10−9 by introducing a singly-charged boson S±. We show numerical analysis of neutrino oscillation, lepton flavor violations, Z boson decays, and demonstrate our allowed regions in cases of normal and inverted hierarchies. We find the sizable scale of muon anomalous magnetic dipole moment for both cases. Then, we move on to the discussion of dark matter candidates to satisfy the relic density where we have two candidates; fermionic dark matter and bosonic one. And, we classify four cases fermionic dark matter with normal and inverted hierarchies, bosonic one with normal and inverted hierarchies and search for each of the allowed points in the model.