Search

In this work, we present a multiscale real-time approach to study the plasmonic effects of a metal nanoparticle (NP) on the electronic circular-dichroism (ECD) spectrum of a chiral molecule interacting with it. The method is based on the time-evolution of the molecule's time-dependent wavefunction, expanded in the eigenstates of a perturbed Hamiltonian. A quantum description of the molecular system is coupled to a classical representation of the NP via a continuum model. The method is applied to methyloxirane and peridinin at various distances (1, 3, and 5 nm) with respect to a gold NP surface. While no remarkable effect is observed for methyloxirane at any studied distance, an enhancement appears when the peridinin lies at 1 nm and the pulse is linearly polarized perpendicularly to the molecular axis, with the ECD signal centered at 4.1 eV increased by a factor of around 20. These results are rationalized looking at the gap between the plasmonic peak of the NP at around 2.5 eV and the molecular excitations: the smaller the gap between molecular and plasmonic excitations, the larger the plasmonic enhancement of the ECD signal. Moreover, ECD peaks are selectively enhanced due to the favorable coupling between the pulse polarization and the combined effect of electric and magnetic dipole moments. This approach allows one to go through the electronic structure and dynamics of chiral molecules for obtaining a realistic description of plasmon-mediated ECD spectra, e.g., paving the way to applications to molecules of biological relevance interacting with nanostructures of experimental interest. [ABSTRACT FROM AUTHOR]

Self-propelled particles possessing permanent magnetic dipole moments occur naturally in magnetotactic bacteria and can be built into man-made systems such as active colloids or micro-robots. Yet, the interplay between self-propulsion and anisotropic dipole–dipole interactions on dynamic self-assembly in three dimensions (3D) remains poorly understood. We conduct Brownian dynamics simulations of active dipolar particles in 3D, focusing on the low-density regime, where dipolar hard spheres tend to form chain-like aggregates and percolated networks with increasing dipolar coupling strength. We find that strong active forces override dipolar attractions, effectively inhibiting chain-like aggregation and network formation. Conversely, activating particles with low to moderate forces results in a fluid composed of active chains and rings. At strong dipolar coupling strengths, this active fluid transitions into an active gel, consisting of a percolated network of active chains. Although the overall structure of the active gel remains interconnected, the network experiences more frequent configurational rearrangements due to the reduced bond lifetime of active dipolar particles. Consequently, particles exhibit enhanced translational and rotational diffusion within the active fluid of strings and active gels compared to their passive counterparts. We quantify the influence of activity on aggregate topology as they transition from branched structures to unconnected chains and rings. Our findings are summarized in a state diagram, delineating the impact of dipolar coupling strength and active force magnitude on the system. [ABSTRACT FROM AUTHOR]

A deterministic, bright, room-temperature stable single-photon source (SPS) has been a major demand in the field of quantum photonics. Here, using computational and analytical techniques, we showed that the Mie-scattering moments of an all-dielectric cavity-cum-antenna help in shaping the spontaneous emission process of an embedded point-dipole emitter, the nanodiamond-based NV − and SiV color centers here. Our resonator-cum-antenna design comprises two top and bottom TiO 2 cylinders with a sandwiched polyvinyl alcohol (PVA) layer enclosing the nanodiamond crystal. The Cartesian multi-polar decomposition of the Mie-scattering moments of the sandwiched PVA layer (enclosing the dipole emitter) with subwavelength scale thickness showed strong electric-dipole (ED) resonance. This resulted in significant field confinement, making the PVA layer to act as a cavity, providing a Purcell enhancement of more than an order of magnitude for all dipole orientations. The top and bottom TiO 2 cylinders were observed to act as an antenna, and the far-field radiation pattern of the embedded dipole-emitter is controlled by the Mie-scattering moments of the TiO 2 cylinders. The radiation directionality along the vertical directions was found to be maximum at the Kerker point (electric dipole moment, ED = magnetic dipole moment), the collection efficiency (CE) being about 80%. For dipole emission coupled to the antenna, the quantum efficiency was observed to increase to a high value of 0.98 for nanodiamond NV − center, very close to an ideal case of purely radiative emission. Our scheme is shown to be universal and can be applied to any solid-state-based quantum emitters, for generating on-demand SPS for quantum-photonic applications. [ABSTRACT FROM AUTHOR]

At optical frequencies, the collective excitation of the periodic array of metallic meta-molecules can support surface lattice resonances (SLRs) due to the coupling of localized surface-plasmon (LSP) resonances to Rayleigh anomaly diffraction. However, the LSP effect in metal blocks becomes negligible in the microwave region. Thus, how the SLRs behave in the microwave regime is very interesting. In this paper, a microwave metasurface consisting of periodic metallic cubes on an ultrathin dielectric substrate is investigated. Two high-Q transmission dips are found, which can be attributed, respectively, to electric-dipole SLRs (ED-SLRs) and magnetic-dipole SLRs (MD-SLRs), because of the non-resonant Rayleigh-like scattering of single cubes and diffraction coupling of the periodic array. The frequencies of both ED- and MD-SLRs are sensitive to the refractive index of the substrate, suggesting that the proposed metasurface may be used to measure the refractive index in the microwave range. [ABSTRACT FROM AUTHOR]

This paper aims at the theoretical study of the CO2 magnetic-dipole ν2 + ν3 rovibrational absorption band that was recently detected in the Martian atmosphere. Specific characteristics of the magnetic dipole operator are carefully examined. Our evaluation of the magnetic-dipole line intensities is based on the variational calculations and the use of molecular properties is determined through specially performed ab initio quantum chemical calculations. The comparison of our simulated magnetic-dipole spectrum with available laboratory taken data also requires the knowledge of line intensities in the quadrupole band, which partially overlaps with that magnetic-dipole. Quadrupole intensities, once reconsidered, are permitted to correct previously reported values of the integrated intensity as well as the intensity of selected branches. The sum of our calculated magnetic-dipole and quadrupole rovibrational lines is shown to be in good agreement with both sets of presently available data from FTIR and OFCEAS laboratory observations. [ABSTRACT FROM AUTHOR]

On the ground of multi-reference configuration interaction calculations with an account of spin–orbit coupling, we have predicted the probability of two unknown spin-forbidden transitions in the spectrum of the N2 molecule: the electric dipole A′5Σg+ → A3Σu+ emission system and the magnetic dipole a′1Σu− ← A3Σu+ transition. The radiative lifetime of the lowest A′5Σg+ sublevel is less than a microsecond; the magnetic transition induced by the spin current in the triplet state is predicted with relatively low oscillator strength (f = 10−10), which still could be detectable. [ABSTRACT FROM AUTHOR]

Perfect magnetic mirrors are important optical devices for the development of novel optical detectors, solar cells, and imaging devices. They have the property of only reversing the magnetic field of a light wave upon reflection, for instance, in functional optical metasurfaces. To design an optical magnetic mirror, high-refractive-index dielectric nanostructures that support strong magnetic dipole (MD) response in the optical wavelength range are used. However, the spectral overlap between the MD and electric dipole in dielectric resonators degrades the magnetic mirror reflection. Here, we propose and demonstrate a perfect optical magnetic mirror metasurface that totally reflects an incident wave without electric field phase change. In this perfect magnetic mirror, the electric dipole radiation is completely suppressed by the radiation of the anapole mode in the spectral range where the destructive interference between the electric dipole and toroidal dipole occurs. By fine-tuning the size parameters of the dielectric resonators, we show near-perfect MD scattering as a result of the spectral overlap between MD resonance and anapole mode. The optical magnetic mirror can be tuned from the visible to near-infrared range by scaling the sizes of the resonators. The MD scattering resonators promote the perfect magnetic mirror, a promising platform for designing photodetectors, biological sensors, and reflected waveplates. [ABSTRACT FROM AUTHOR]

In order to solve the problem of magnetic targets magnetic field modeling, a magnetic dipole array model was established, a modeling inversion equation system was constructed, and the degree of sickness of the solved equation system under different numbers of magnetic dipoles was quantitatively analyzed based on the coefficient matrix condition number. In order to solve the problem of the pathological system of magnetic field modeling equations, a regularization method based on the conjugate gradient least squares method was designed to invert the magnetic moment parameters of the magnetic dipole. In order to analyze the applicability of the regularization method in magnetic field modeling inversion, the magnetic moment solving accuracy, the magnetic moment solving robustness, calculation time, and other metrics are defined. A detailed test of the ship model was designed, and the magnetic field passing characteristics of the two types of ship models at different positive and horizontal conditions at two depths were measured. Under the condition of no interference and interference, the conjugate gradient least squares method is used to invert the magnetic field model, and the numerical test analysis shows that the conjugate gradient least squares method has higher applicability than the generalized inverse solution method and the stepwise regression method. Under the condition of interference, the relative error of magnetic field fitting of the array model with 15 magnetic dipoles is 0.1537, and the relative error of magnetic field extrapolation is 0.0868. The method proposed has the advantages of high accuracy and strong robustness in solving the magnetic moment of the magnetic dipole array model. [ABSTRACT FROM AUTHOR]

We implement a distributed Bragg reflector (DBR) laser diode (LD) package with low-magnetic field generation. The package consists of a commercial 795 nm DBR LD chip, a thermo-electric cooler (TEC), a thermistor, a flexible printed circuit board (FPCB) which cancels the magnetic field emitted by the TEC current flow, and a non-magnetic aluminum case. We confirm that the magnetic dipole moment of our low-magnetic package body is about three orders of magnitude smaller than that of a commercial DBR laser package. Moreover, it is shown that our compensating FPCB, the effectiveness of which is supported by computer simulations, reduces the magnetic field magnitude by a factor of 2.2. The FPCB also reduces the magnetic field gradient emitted by the TEC current flow so that gradient-induced spin relaxations are suppressed in applications. A portable optically pumped atomic magnetometer (OPAM) utilizing two low-magnetic packages as light sources is reported as an application of the package and shows a 0.30 pT/Hz1/2 level magnetic sensitivity at a 69 μT external magnetic field; in contrast, the OPAM utilizing the commercial packages showed a magnetic sensitivity of 0.87 pT/Hz1/2. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate that the direction and intensity of the magnetic dipole emission can be manipulated simultaneously by using spoof plasmonic structures. First, by placing two spoof plasmonic structures around a bare magnetic dipole source, we investigate the influence of the orientation of the spoof plasmonic structures on the direction of magnetic dipolar emission. We find that the direction of bare magnetic dipole emission can be freely tuned from 0° to 360° by rotating the two spoof plasmonic structures due to the stimulation of structured magnetic dipolar mode. Furthermore, an array antenna composed of three plasmonic structures is designed; we discuss the manipulation of the intensity and the direction of magnetic dipole emission by three spoof plasmonic structures. The theoretical results show that the intensity of magnetic dipole emission can be effectively enhanced and the direction can be freely selected. In addition, we also investigate the influence of structural variation of the cylinder structure on the intensity and enhancement factor. Our calculated results indicate that the enhancement factor of magnetic dipole emission can reach more than 580 with tuning structural parameters at the resonant frequency of the magnetic dipolar mode. Finally, we discuss the effect of real materials on the external quantum efficiency, and the quantum efficiency is still very high in our design. As such, these results underscore the unique ability of manipulating the intensity and the direction of magnetic dipole emission, opening new technological avenues in the magneto-optical domain. [ABSTRACT FROM AUTHOR]

The dynamo actions of an electrically conducting fluid in a precessing sphere are investigated over a wide range of parameters by direct numerical simulation using a Galerkin spectral method. The focus of this work is to identify the most promising parameter regimes for the dynamo action and to investigate the characteristics of the magnetic field generated by precession. The influence of different nutation angles (30 ° , 60 ° , 90 °) and different precession ratios on the ability to drive dynamo action are investigated. The optimal angle for dynamo actions is found at 90 ° , followed by 60 ° with retrograde precession. A moderate precession ratio around 0.3 is shown to be more feasible for dynamo actions. A rich set of self-sustained dynamo solutions are obtained in the parameter space we explored, including steady, periodic, quasi-periodic, and turbulent dynamos. The structure of the generated magnetic fields is analyzed by using helical wave decomposition. None of the precession driven dynamos we obtained produce a predominantly dipolar field, contrary to the convection driven dynamos. The long-time evolution of the magnetic dipole moment is investigated and different types of polarity reversals are observed. [ABSTRACT FROM AUTHOR]

To evaluate the long-distance magnetic field generated by neurons, we propose a reformulation of the brain's magneto-quasistatic approximation based on the Jefimenko's time-dependent generalization of the Biot–Savart law. This differs from the traditional approach relying on Maxwell's equations and not on their general solution. Instead of a typical length of the medium in the conventional approach, we use the signal traveling distance | r − r ′ ¯ | , from the farthest source point r ′ ¯ to the field point r , as the proper length to define the quasistatic dynamics. We consider relatively low frequencies below a typical value f max = 100 Hz. The quasistatic approximation is justified since (2 π f max) 2 | r − r ′ ¯ | 2 ϵ μ 0 ≈ 4 × 10 − 7 ≪ 1. We take | r − r ′ ¯ | ≈ 0.1 m , with the gray matter permittivity, previously underestimated, to be ϵ ≈ 10 7 ϵ 0. A formalism for the long-distance magnetic field generated by neuronal populations is then developed. Each population is described as a region of small dimensions compared to the average distance from the field point. We split the impressed current density into synaptic and action potential contributions and study their magnetic field. Assuming a small contribution of the impressed currents at the region boundary surface, we obtain two equivalent expressions of the synaptic current dipole moment in terms of the scalar potential and/or its spatial derivatives. Using Maxwell–Wagner's time, the synaptic current dipole moment of a region is also shown to be related to the electric dipole moment of each part with uniform conductivity and permittivity. Finally, the long-distance magnetic field of action potential currents is expressed in terms of the magnetic dipole moment for these currents. [ABSTRACT FROM AUTHOR]

Manipulation of circularly polarized light (CPL) in the ultraviolet (UV) region holds significant potential for advancing chiral molecules sensing. Recently, chiral metasurfaces have been applied to control CPL in the UV region. However, the spectral selectivity of the existing UV chiral metasurfaces is still limited. Here, we report rod-shaped and ring-shaped metasurfaces sustaining perpendicularly aligned magnetic dipoles (MDs) and capable of inducing narrowband transmission dips. These MDs can be selectively excited in an eccentric ring-shaped metasurface by left-handed and right-handed circularly polarized lights. By exploiting this phenomenon, the selective asymmetric transmission of CPL with opposite handedness within the UV region is reported. A circular asymmetric transmission with a transmittance dissymmetry factor as high as 1.56 and a narrow full width at half maximum of 1.2 nm is achieved. [ABSTRACT FROM AUTHOR]

Circularly polarized light (CPL) carrying spin angular momentum is crucial to many applications, such as quantum computing, optical communication, novel displays, and biosensing. Nonetheless, the emission from chiral molecules contains comparable CPL components with opposite handedness, resulting in low levels of CPL overall with a small dissymmetry factor and fixed handedness consistent with the handedness of the molecules. Nanoantennas have proved to be useful tools for controlling the emission properties of quantum emitters. In particular, dielectric resonators support electric and magnetic modes, which implies unparalleled opportunities to interact with chiral molecules whose emission originates from both electric and magnetic dipole transitions. In this work, we theoretically study the effects of a spherical dielectric nanoantenna on the directionality and polarization of emission from a chiral molecule. With exact analytical solutions based on generalized Mie theory, we show that directional chiral light emission and nontrivial polarization modulation, such as handedness reversal or chirality enhancement, can be achieved simultaneously for a chiral dipole tangentially coupled with a silicon nanosphere. The influence of the relative strength and orientation between the electric and magnetic dipole moments is also discussed. Our results suggest a new approach to controlling chiral dipolar emission and could benefit the development of chiral light sources. [ABSTRACT FROM AUTHOR]

Electrical control of magnetization or magnetic control of polarization offers an extra degree of freedom in materials possessing both electric and magnetic dipole moments, viz., magnetoelectric (ME) multiferroics. A microstructure with polycrystalline configurations that enhances the overall polarization/magnetization and that outperforms single crystalline configurations is identified in a 1–3 CoFe 2 O 4 –BaTiO 3 (or CFO–BTO) composite. The characterization of local fields corresponding to the polycrystal configuration underlines a nontrivial role played by randomness in better cross coupling mediated by anisotropic and asymmetric strains. The microscopic field (local field) profile of the composite provides rich information regarding the distribution of key parameters central to the magnetoelectric effect. The differential contractual stress level observed in the local stress profile of CFO–BTO composite upon applying an external magnetic field conforms with the previous experimental magnetostriction observed in CFO. The role played by residual stresses stemming from misalignment of the polarization in the neighboring grains in enhancing the ME coupling is briefly discussed. [ABSTRACT FROM AUTHOR]

We consider the design of magnetic mirrors that consist of a layer of two-dimensional high-refractive-index dielectric particles. The central idea is to search for conditions for which the electric field of the light backscattered by a single particle has a zero phase difference with respect to the incident field. Employing physical arguments, we conclude that this can occur when the electric dipolar contribution vanishes. Optimizing the form of the cross section, we find a situation in which the vanishing of the dipolar contribution coincides with an in-phase condition for the magnetic dipole and the electric quadrupole contributions. The resulting scattering pattern of the particle resembles that of an electric dipole, with the difference that the forward and backscattered electric fields have opposite signs. Based on these results, we design a metasurface reflector that behaves as a magnetic mirror at a specific wavelength within a wideband spectral response. Subsequently, we extend the results to the design of supported structures where a magnetic mirror condition at a single wavelength is similarly found. [ABSTRACT FROM AUTHOR]

A novel phenomenon is observed in the meta-atoms composed of a complementary rectangular double split-ring resonator (SRR). An intrinsic Fano-resonance collapses with the outer SRR deformed asymmetrically. Alternatively, a trapped mode emerges at an adjacent frequency region, of which its strength grows up with increasing the asymmetric deviation. However, the asymmetric deformation in the inner SRR has influence neither on the evolution of this intrinsic Fano-resonance nor on the excitation of the aforementioned trapped mode. The results of electromagnetic field simulation indicate that an interference of two magnetic dipoles leads to the intrinsic Fano-resonance on the outer SRR. The asymmetric deviation destructs coherent interference so that the Fano-resonance collapses. To the trapped mode, the surface current passes through the metal gap of the outer SRR, leading to a couple of antiparallel currents, which results in a couple of magnetic dipole oscillations. The intrinsic modes are kept constant, even though the inner SRR is asymmetrically deformed. The outer SRR plays the role of a Faraday cage, which electromagnetically shields the trapped mode on the inner SRR. [ABSTRACT FROM AUTHOR]

We present circuit-loaded metasurfaces that behave differently in a passive manner even at the same frequency in accordance with the incoming waveform, specifically its pulse width. Importantly, the time-varying waveform-selective metasurfaces reported thus far were mostly able to change their electric properties but not their magnetic properties; this severely limited the design range of their corresponding wave impedances and refractive indices and thus hindered the development of potential applications in antennas, sensors, imagers, signal processing, and wireless communications. In this study, passive time-varying waveform-selective metasurfaces were found to attain magnetic property control by introducing an additional circuit-loaded layer that generated an artificial magnetic dipole moment; this magnetic moment only occurred during the designed pulse duration in the time domain. Our proposed concept and structures were validated numerically and experimentally; thus, our results could be used to address electromagnetic and related issues sharing the same frequency component via the variation of the pulse width as an additional degree of freedom. [ABSTRACT FROM AUTHOR]

This study investigates the three-dimensional problem of steady ferrofluid deposition on an inclined rotating surface in the presence of a magnetic dipole. A finite element procedure is used to solve normalized ordinary differential equations derived from momentum and energy equations. The current numerical model and its solution is compared and validated against previous numerical results. The velocity and temperature field variations are a representation of the effects of magnetic field-based viscosity, magnetic polarization force, Curie temperature, and Prandtl number. In addition, some common errors in the similarity transformation for inclined rotating disk flows are addressed in the present study. The results show that the magnetic field-dependent viscosity generated by the magnetic torque in the current flow reduces the velocity of the thin film liquid in all directions, including rotational flow (radial, tangential, and axial) and inclined flow (drainage and induced). Moreover, the local heat transfer between the fluid and the surface of the rotating disk increases with a rise in the ferromagnetic interaction number and Prandtl number. These findings imply that ferrofluids could be effective for cooling electronic devices in the presence of a magnetic dipole. [ABSTRACT FROM AUTHOR]

We demonstrate numerically that, through energy minimization on large spin lattices, one can write skyrmions in a thin magnetic film with a magnetic dipole of a few tens of nanometer in size. Nucleation of non-chiral skyrmions as well as chiral skyrmions formed by the Dzyaloshinskii-Moriya interaction has been investigated. Analytical model is developed that agrees with the numerical results. It is shown that skyrmions can be written through a number of scenarios that depend on the experimental technique and parameters of the system. In one scenario, which branches into subscenarios of different topology, the magnetic dipole on approaching the film creates a skyrmion-antiskyrmion pair. As the dipole moves closer to the film, it induces collapse of the antiskyrmion and creation of a non-zero topological charge due to the remaining skyrmion. In a different scenario, the dipole moving parallel to the film nucleates a skyrmion at the boundary and then drags it inside the film. Possible implementations of these methods for writing topologically protected information in a magnetic film are discussed. [ABSTRACT FROM AUTHOR]

Radiation energy scattered by a small particle can be expected to travel from the particle to a detector in the far field along the field lines of the Poynting vector. We consider the scattering off a small conducting sphere, for which only the induced electric and magnetic dipole moments contribute to the emitted radiation. Field lines of the energy flow due to interference between fields radiated by the electric and magnetic dipoles appear to form closed loops in the vicinity of the particle. Energy flows out of the particle at one side and then returns to the particle at the other side, and as such, this energy flow does not contribute to the radiated power. At larger distances, energy flows away from the particle at one side of the particle, but on the other side, radiation flows from infinity toward the particle. The energy for the scattered radiation is provided by the incident field. The energy flow is due to interference between the incident field and the scattered radiation, known as extinction. The flow pattern of this energy exhibits numerous singularities and vortices, and closed-loop flows near the particle. In the far field, energy flows along counter-oriented field line bundles, with only the net power flowing inward. [ABSTRACT FROM AUTHOR]

Magnetic Field Assisted Additive Manufacturing (MFAAM) enables 3D printing of magnetic materials of various shapes which exhibit a complex anisotropy energy surface containing contributions generated from different origins such as sample, particle, and agglomerate shape anisotropy, flow and field induced anisotropy, and particle crystal anisotropy. These novel magnet shapes require the need to measure the x, y, and z components of the magnetic dipole moment simultaneously to fully understand the magnetic reversal mechanism and unravel the complex magnetic anisotropy energy surface of 3D printed magnetic composites. This work aims to develop a triaxial vibrating sample magnetometer (VSM) by adding a z-coil set to a pre-existing biaxial VSM employing a modified Mallison coil set. The optimum size and location of the sensing coils were determined by modeling the sensitivity matrix of the z-coil set. The designed coil set was implemented using 3D printed spools, a manual coil winder, and gauge 38 copper wire. A 3D printed strontium ferrite nylon composite sample was used to estimate the sensitivity of the z-coils (50 mV/emu). The results herein are applicable for any VSM using a modified Mallison biaxial coil configuration allowing for a quick implementation on pre-existing systems. [ABSTRACT FROM AUTHOR]

Multidimensional spin-selective manipulation of optical waves is crucial for various intriguing applications in modern nanophotonics, such as quantum-information processing and chiral sensing and imaging. In this work, we observed giant broadband asymmetric transmission of circularly polarized waves and spin-preserving reflection, together with near-unity transmission circular dichroism, in a planar chiral metasurface composed of high-index transition-metal-dichalcogenide nanoantennas with large material anisotropy. The perpendicular and parallel electric and magnetic dipole moments excited in the nanoantennas under circularly polarized waves are explored to account for the asymmetric transmission and optical chirality. Combined with the Pancharatnam–Berry phase, we achieved the wavefront manipulation for transmitted circularly polarized waves with an efficiency approaching 91.5% and spin-selective focusing of an incident light via a metasurface metalens. Our work will pave the way for studying the multidimensional manipulation of optical spins through engineering transition-metal-dichalcogenide-based metasurfaces. [ABSTRACT FROM AUTHOR]

High Q-factor resonance holds great promise for bio-chemical sensing and enhanced light–matter interaction. However, terahertz (THz) magnetic resonances usually demonstrate low Q-factors, resulting in huge energy radiation loss particularly in high frequency bands. Here, we show that high Q-factor magnetic dipole resonance at THz frequencies can be achieved by exploiting the coherent Fano interactions with strong field enhancements in an array composed of single metallic split-ring resonators, working at Wood–Rayleigh anomalies. It can give rise to ultrahigh Q-factor beyond 104 in the THz regime. Experimentally, the measured Q-factor of dominant magnetic dipole resonance can achieve no less than a level of ∼261 by Lorentzian fitting to the experimental data. In addition, a high Q-factor of the fundamental-order magnetic dipole resonance is demonstrated beyond 30. High-Q magnetic dipole resonance is closely associated with ultralow-damping and negative permeability in the THz band. The measurements of magnetic dipole resonances are in good agreement with the theoretical analyses. Our scheme suggests a feasible route to suppress radiative loss for enhanced THz field-matter interaction. [ABSTRACT FROM AUTHOR]

Optical properties are numerically studied of a plasmonic planar 2D noble metal nanostructure with the design inspired by Babinet's principle. We stack a 2D array of nanodisks and a complementary screen—2D periodically perforated film—so that they are separated by a dielectric spacer. Near-field interaction between electric and magnetic dipoles induced in metal metasurfaces results in increased reflectance and suppressed absorption, canceling out initial resonances in the individual nanostructures. The proposed metasurface has polarization- and angle of incidence-independent response in a wide frequency range as compared to the resonance bandwidth. The proposed design is robust to possible structural imperfections. [ABSTRACT FROM AUTHOR]

We analyze the rotational dynamics of six magnetic dipoles of identical strength at the vertices of a regular hexagon with a variable-strength dipole in the center. The seven dipoles spin freely about fixed axes that are perpendicular to the plane of the hexagon, with their dipole moments directed parallel to the plane. Equilibrium dipole orientations are calculated as a function of the relative strength of the central dipole. Small-amplitude perturbations about these equilibrium states are calculated in the absence of friction and are compared with analytical results in the limit of zero and infinite central dipole strength. Normal modes and frequencies are presented. Bifurcations are seen at two critical values of the central dipole strength, with bistability between these values.

Silicon metasurfaces have been attracting interest in the sensing field because of their ability to support magnetic Mie resonance, low optical heating, and CMOS-compatible fabrication processes. Herein, we demonstrate that the sensitivity of the magnetic dipole (MD) mode for nanodisk Mie resonators (as high as 385 nm/RIU) is similar to the sensitivity of plasmonic metasurfaces and greater than that of the electric dipole (ED) mode of nanodisk Mie resonators. We also engineer the thickness of Mie resonators to achieve an MD-mode linewidth as small as 0.56 nm and a figure of merit greater than 160 RIU−1. The measured sensitivity of the MD mode is more accurate than that of the ED mode, which is more prone than the MD mode to measurement errors arising from the partial filling of the liquid. Our study paves the way for the development of MD-mode-based dielectric biosensors for use in personal healthcare and medical diagnosis. [ABSTRACT FROM AUTHOR]

Trajectories of charged particles in two-dimensional axisymmetric magnetic fields bear obvious resemblance to epicyclods. The main focus of this study is the systematic assessment of the accuracy of the epicycloid approximation for particle trajectories under such conditions. We primarily discuss particle motion constrained to the equatorial plane of a magnetic dipole. It is shown that with well chosen epicycloid parameters, this approximation can remain accurate for conditions well outside the area of expected validity of the Guiding Center approach. Calculating the epicycloid parameters using exact results for particle motion in the equatorial plane of a magnetic dipole allows to retain the accuracy of this approximation to surprisingly high particle energies. We also show that this approach allows us to approximate the trajectory of a charged particle more accurately than its velocity. [ABSTRACT FROM AUTHOR]

The problem of the charged-particle motion in an axisymmetric magnetic-dipole geometry is used to assess the validity of Hamiltonian guiding-center theory, which includes higher-order corrections associated with guiding-center polarization induced by magnetic-field nonuniformity. When a magnetically confined charged-particle orbit is regular (i.e., its guiding-center magnetic moment is adiabatically invariant), the guiding-center approximation, which conserves both energy and azimuthal canonical angular momentum, is shown to be faithful to the particle orbit when guiding-center polarization effects are taken into account. [ABSTRACT FROM AUTHOR]

This document explores the experimental and theoretical aspects of a magnetically coupled oscillator system with two swinging magnets. The setup is designed to allow for long-lasting oscillations and is cost-effective by utilizing a smartphone magnetometer to measure the dipole moment of the magnet and record the period of the oscillations. The document discusses various setups and approaches used in studying magnetically coupled oscillators, and presents a simplified setup that uses a low-friction pivot and a smartphone for data recording. The physical setup, theoretical model, and experimental results are described in detail. The document concludes by suggesting that this setup can be a valuable addition to existing experiments on coupled oscillators. [Extracted from the article]

We present coupled cluster calculations of NMR shielding constants of aluminum, gallium, and indium in water-ion clusters. In addition, relativistic and dynamical corrections and the influence of the second solvation shell are evaluated. The final NMR shielding constants define new absolute shielding scales, 600.0 ± 4.1 ppm, 2044.4 ± 31.4 ppm, and 4507.7 ± 63.7 ppm for aluminum, gallium, and indium, respectively. The nuclear magnetic dipole moments for 27Al, 69Ga, 71Ga, 113In, and 115In isotopes are corrected by combining the computed shielding constants with experimental NMR frequencies. The absolute magnitude of the correction increases along the series and for indium isotopes it reaches approximately -8.0 × 10-3 of the nuclear magneton. [ABSTRACT FROM AUTHOR]

We study a hybrid system composed of a chiral quantum dot and a dielectric nanoparticle subjected to an electromagnetic wave. We aim to show that the hybrid system features synergistic properties caused by interactions between its components. We solve the Bloch equation for the density matrix of the chiral quantum dot modeled as a two-level system with transition electric and magnetic dipole moments. We show that the system acts as a bianisotropic meta-atom: The electric polarization (magnetization) can be induced by the incident magnetic (electric) field. The electromagnetic and magnetoelectric polarizability dyadics of the hybrid system are influenced by the nanoparticle size and separation and the intensity and polarization of the incident wave. Due to the self-interaction of the quantum dot in the presence of the nanoparticle, the system exhibits optical activity and circular dichroism spectra of different character in Fano, double peaks, weak transition, and strong transition regions of the parameter space. Notably, in the strong transition region, the optical activity and circular dichroism spectra become discontinuous and dependent on the initial state of the system. The magnetic dipole moment induced in the dielectric nanoparticle plays a key role: Indeed, unlike the isolated chiral quantum dot, the hybrid system exhibits strong circular dichroism in a broad frequency range. The chiral quantum dot-dielectric nanoparticle meta-atom offers unique opportunities for creating low-loss all-dielectric meta-surfaces operating in the visible spectral range. [ABSTRACT FROM AUTHOR]

Four configurations of a rotating magnetic dipole-driven turbulent flow in an electrically conducting liquid cylinder are considered by spectral direct numerical simulation. These configurations differ by parallel or perpendicular orientation of the dipole rotation vector with respect to the nearest surface of the cylinder or its axis. The rotating dipole generates electromagnetic force in a thin outer liquid layer facing it. A concentrated vortex is driven when the dipole rotation vector is perpendicular to the nearest surface. This vortex closely resembles the rotating disk-driven flow. When the dipole rotation vector is parallel to the nearest surface, then a distributed vortex occurs akin of the translating wall-driven cavity flow. The characteristic velocity is comparably little influenced by dipole orientation despite the electromagnetic force magnitude varying by a factor of three. Perpendicular orientation of the magnetic dipole rotation vector with respect to the cylinder's axis causes secondary corner eddies increasing the overall turbulent fluctuation. The simulations are supplemented by an experiment featuring a deep and narrow funnel-shaped quasi-stationary free surface deformation above a concentrated vortex. [ABSTRACT FROM AUTHOR]

The mathematical form of the magnetic field due to a current loop, and the fact that it is identical to the electric field due to an electric dipole in the far field, are fundamental to our understanding of electromagnetism. While undergraduate level electromagnetism textbooks usually derive the electric field from an electric dipole, few derive the magnetic field from a current loop. Most simply state it without proof, or perform the derivation for simpler cases such as the on-axis field. Those that perform the derivation use the magnetic vector potential, a relatively advanced concept that most undergraduate students would not encounter until their final year of study, if at all. Here, a simple derivation to obtain the magnetic field due to a current loop in the far-field approximation is presented. The derivation begins from the Biot–Savart law and does not require the vector potential. The problem is set up so that only a single integration is necessary (from angle α = 0 to α = 2π around the current loop), and the result is compared with that for the electric field surrounding an electric dipole. [ABSTRACT FROM AUTHOR]

Currently, when the existing magnetic dipole inversion methods are used, the classification process heavily relies on the localization results, and the localization error can significantly deteriorate the classification results. In order to address this problem, the present study proposes a novel magnetic dipole inversion method based on tensor geometric invariants, in which localization and classification processes are mutually independent. First, based on tensor geometric invariants, it was proved that the cross product between the intermediate eigenvectors at any two measurement points in the dipole magnetic field is either in the same direction as the magnetic moment vector or in the opposite direction. Accordingly, the direction of the magnetic moment vector could be directly obtained. Next, based on tensor geometric invariants, nonlinear equations including the position parameters of the dipole were constructed so as to derive the position of the dipole. By employing the proposed method, localization and classification were found to be two mutually independent processes, both of which are relatively insensitive to attitude changes of the measurement system. The present simulation results demonstrate that the proposed method is superior to the scalar triangulation and ranging (STAR) method, the Nara improved method, and the STAR improved method in both classification and localization performance. Moreover, the proposed method exhibits the strongest noise immunity and can be effectively used for real-time inversion. [ABSTRACT FROM AUTHOR]

The influence of the intermolecular magnetic dipole-dipole interaction on the free induction decay (FID) as well as on the Hahn-echo of proton spins in polymer melts is investigated. It is shown that for isotropic models of polymer dynamics, when polymer segment displacements do not correlate with an initial chain conformation, the influence of the intermolecular magnetic dipole-dipole interactions to the FID and Hahn echo is increasing more rapidly with evolution time than the corresponding influence of the intramolecular magnetic dipole-dipole interactions. On the other hand, the situation is inverted for the tube-reptation model: here the influence of the intramolecular magnetic dipole-dipole interactions to the FID and Hahn echo is increasing faster with time than the contribution from intermolecular interactions. A simple expression for the relative mean squared displacements of polymer segments from different chains is obtained from the intermolecular contribution to the FID. A modified Anderson-Weiss approximation, taking into account flip-flop transitions between different spins, is proposed and on that basis, the conditions for extracting the relative intermolecular mean squared displacements of polymer segments from the intermolecular contribution to the proton FID is established. Systematic investigations of intermolecular contributions, which were considered as an unimportant factor for FID and Hahn echo in polymer systems by most previous works, actually cannot be considered as negligible and opens a new dimension for obtaining information about polymer dynamics in the millisecond regime. [ABSTRACT FROM AUTHOR]

The electromagnetic drag force and torque acting on a magnetic dipole due to the translatory motion of an electrically conducting bar with square cross section and infinite length is computed by numerical analysis for different orientations and locations of the dipole. The study is motivated by the novel techniques termed Lorentz force velocimetry and Lorentz force eddy current testing for noncontact measurements of the velocity of a conducting liquid and for detection of defects in the interior of solid bodies, respectively. The present, simplified configuration provides and explains important scaling laws and reference results that can be used for verification of future complete numerical simulations of more realistic problems and complex geometries. The results of computations are also compared with existing analytical solutions for an infinite plate and with a newly developed asymptotic theory for large distances between the bar and the magnetic dipole. We finally discuss the optimization problem of finding the orientation of the dipole relative to the bar that produces the maximum force in the direction of motion. [ABSTRACT FROM AUTHOR]

Focuses on the magnetic dipole transition of the oxygen molecule, B[sup ′] [sup 3]Π[sub g]←X [sup 3]Σ[sub g]([sup -](0,0), using an isotopically pure gas. Consistency of the location, structure and intensity of the Schumann-Runge band with expectatoin for the magnetic dipole transition of the oxygen molecule. [ABSTRACT FROM AUTHOR]

In this study, we investigated the interaction between skyrmions in Brownian motion at room-temperature. Cells containing two skyrmions were implemented by controlling the magnetic anisotropy in the Ta/CoFeB/Ta/MgO/SiO2 structure. The interaction between skyrmions was investigated by fabricating a circuit with two cells in close proximity to each other. It was found that the minimum value of the correlation coefficient was −0.234. These results show that the Brownian motion of skyrmions can potentially realize unconventional computing such as stochastic calculations and ultra-low power computing. [ABSTRACT FROM AUTHOR]

As a magnetic confinement configuration for electron-positron pair-plasmas, the APEX collaboration [T. S. Pedersen et al., New J. Phys. 14, 035010 (2012)] plans to construct a compact levitated dipole experiment with a high-temperature superconducting coil. In order to realize stable levitation of the dipole field coil, a simple feedback-controlled levitation system was constructed with conventional analog circuits. We report the properties of a prototype levitation system using a permanent magnet and compare its behavior to predictions from a stability analysis. We also present a practical review needed for the construction of a compact levitated dipole trap system based on the work of Morikawa et al. [Teion Kogaku, J. Cryo. Soc. Jpn. 39, 209 (2004)]. Numerical orbit analysis suggests improved confinement properties of charged particles in a dipole field trap by replacing the permanent magnet with a levitated superconducting coil magnet. Such a compact dipole field configuration is potentially applicable to the confinement of various charged particles including positrons and electrons.

Lossless injection of positrons into a magnetic dipole trap and their subsequent confinement have been demonstrated. Here, we investigate by numerical single-particle simulations how the radial distribution of positrons in the trap is affected by the measurement itself, the choice of injection parameters, the asymmetry of the electric potential, and by elastic collisions. The results are compared to experimental data. A comprehensive understanding of these effects is a milestone on the road to creating an electron–positron plasma in a trap with a levitating superconducting coil. [ABSTRACT FROM AUTHOR]

We study the magnetic domain pattern in a ferrimagnetic CoTb thin film using Lorentz transmission electron microscopy. The evolution of domain patterns is captured at different temperatures and external fields. Magnetic dipole skyrmions and bubbles can be created simultaneously by increasing the temperature of the sample and applying appropriate out-of-plane magnetic fields. By tuning the external magnetic fields, it is found that the skyrmions are annihilated at a higher magnetic field compared to bubbles. Moreover, we also find that the in-plane magnetic field influences the formation and the shape of skyrmions and bubbles. Further, micromagnetic simulations are also consistent with the experimental observations. Our findings provide insights into the magnetic field stability of skyrmions. [ABSTRACT FROM AUTHOR]

The stability of electrically conducting liquid flow in a cylindrical ring channel is studied numerically. The flow is driven by a rotating magnetic dipole placed at the ring's center. Depending on ring's width, two distinct flow regimes are observed. In a narrow ring, the flow itself and its instability resemble the related rotating magnetic field driven flow in a cylinder. This changes in a wide ring when an intense radial jet develops on the midplane. Within this jet, the driving magnetic force is overwhelmed by inertial and viscous forces similar to how it occurs in the boundary layer flow. The instability develops as an azimuthally periodic wave-like deformation of this jet. Non-uniform driving force and the viscous boundary layer at the inner side wall are supposed as the main ingredients of the jet formation. [ABSTRACT FROM AUTHOR]

Luminescence properties of Eu3+ doped germanate glasses containing either silver or gold nanoparticles (NPs) were investigated for excitation at 405 nm. Enhanced emissions and luminescence quenching of the Eu3+ transitions in the range from 570 to 720 nm were observed for samples having various concentrations of metallic NPs. Electric-dipole and magnetic-dipole transitions that originate from the Eu3+ level 5D0 exhibit large enhancement due to the presence of the metallic NPs. The results suggest that the magnetic response of rare-earth doped metal-dielectric composites at optical frequencies can be as strong as their electric response due to the confinement of the optical magnetic field. [ABSTRACT FROM AUTHOR]

Gas-phase NMR spectra of 11B, 10B, and 19F in BF3 are reported, and high-level ab initio calculations of the corresponding NMR shielding constants are described. Extrapolation of the measured resonance frequencies to the zero-density limit ensures that the results correspond to the ab initio values for an isolated molecule. Simultaneous measurements of 3He resonance frequencies and application of the calculated shielding constants allow us to determine improved values of the nuclear magnetic dipole moments of 11B and 10B. The magnetic moments of both isotopes are also determined independently by comparing with the 19F spectral parameters (frequencies and shielding constants). The separately derived nuclear magnetic moments are in good agreement, whereas the literature moments of both 11B and 10B are noticeably less accurate. [ABSTRACT FROM AUTHOR]

Magnetic-field-assisted self-assembly of magnetic-dipole moment carrying aerosol-grown iron nanoparticles on a nonmagnetic substrate results in the formation of magnetic nanoscale rods and bundles thereof. The magnetic dipolar interaction between the bundles essentially drives the formation of regular patterns of bundle density modulations in the two-dimensional array of elastically deformable magnetic rods. This pattern formation is shown to belong to the class of physical systems undergoing spinodal decomposition. Possible applications for dipolar magnetic nanorods in the fields of perpendicular storage media and ferrofluids are highlighted. A giant magnetoviscous effect is expected. [ABSTRACT FROM AUTHOR]