Magnitude Of External Magnetic Field Research Articles

Spin-dependent resonant Andreev tunneling in hybrid ferromagnetic metal–magnetic quantum dot–superconductor nanostructures

There exists a variety of theoretical proposals to transform states induced by magnetic nanoparticles inside a superconducting gap into Majorana fermion states. The main challenge in this route is a conclusive proof and undoubted distinguishing between topologically trivial subgap Andreev bound states and topologically nontrivial magnetically polarized Majorana bound states. This motivated us to investigate a nonequilibrium electrons tunneling through a ferromagnetic normal metal–magnetic quantum dot–s-wave superconductor (F-mQD-SC) nanostructure, where the mQD’s discrete levels are spin splitted. By using the Keldysh Green’s function method, the expressions for a tunnel current and probability of the Andreev reflection (AR) versus energy are derived and studied. We find that the system’s resonant ARs conductance exhibits different kinds of peaks depending on a spin splitting of the mQD levels, the spin polarization magnitude of the F-lead current, the gate voltage, and an external magnetic field magnitude. The nanostructure’s conductance versus a bias voltage exhibits extra peaks which at some combination of its parameters can mimic ones expected for Majorana modes in a topological superconducting state. The distinguishing transport characteristics of a F-mQD-SC nanoscale structure being in non-topological state are discussed. We suggest that the results obtained can provide helpful clarification for understanding recent experiments in superconductor–ferromagnet hybrid nanostructures with topologically protected excitations.

Strain sensitivity and microscopic deformation mechanism of graphene foam containing active nanoparticles under magnetic fields

Magnetic aerogels have attracted many practical applications in recent years, which requisites a comprehensive understanding on basic mechanics of this hybrid composite system. In this paper, the microscopic deformation mechanism and strain variation (εΔ) of such a hybrid material under external magnetic field (Ef) is systematically studied by the coarse-grained molecular dynamics simulation method. The major factors like layer thickness, magnitude of external magnetic field and crosslinks effects are mainly considered. The recovery behavior is also studied under cyclic Ef. Interestingly, the εΔ of such a hybrid material is much affected by the graphene sheet thickness, magnitude of applied Ef and crosslinks, due to their direct influences on the microstructural evolution. The εΔ of non-bonded hybrid composite with single layer thick graphene sheet (εΔ⁓0.19) is four times higher relative to eight layers thick system (εΔ⁓0.045). With the increase of graphene sheet thickness, the microstructural evolution of nanoparticles will change from wrapping of single layer sheets around them to flow and jump from one thick sheet to other. We also found the critical value of Ef, i.e., 200 nN for single layer thick graphene sheet hybrid systems beyond which the εΔ tend to decrease, however, εΔ for eight layers system continue to increase as a function of Ef magnitude. The addition of crosslinks remarkably enhances the εΔ (⁓0.74) and recovery (⁓90%) of hybrid composite system. The bonded nanoparticles initiate the folding and unfolding mechanism of graphene sheets during cyclic Ef. The results clarify the micro mechanism and basic mechanics of magnetic aerogels that will be helpful to the design the future devices and advanced sensors.

Magnetoelectric effect in three-layered gradient LiNbO3/Ni/Metglas composites

The effect of annealing in a permanent magnetic field on the magnitude of magnetoelectric coefficient in three-layered gradient magnetoelectric LiNbO3/Ni/Metglas composites has been studied. A method of electrochemical nickel deposition on bidomain lithium niobate crystals has been demonstrated. We show that the optimum annealing temperature in a permanent magnetic field for the generation of the highest remanence in the Ni layer is 350 °C. The specimens annealed at this temperature exhibit the greatest shift of the magnetoelectric coefficient dependence on external magnetic field magnitude relative to the value Hdc = 0. The quasi-static magnetoelectric coefficient in the absence of an external magnetic field proves to be 1.2 V/(cm ∙ Oe). The highest magnetoelectric coefficient that has been achieved at a bending structure resonance frequency of 278 Hz proves to be 199.3 V/(cm ∙ Oe) without application of an external magnetic field. The experimental magnetoelectric coefficient figures for three-layered gradient LiNbO3/Ni/Metglas composites are not inferior to those for most magnetoelectric composite materials reported earlier.

Magnetic properties of a hexagonal nanowire system with mixed spin: Application of the stochastic Glauber dynamics with mean-field approximation

The Glauber stochastic dynamics with mean-field approximation has been applied to study the magnetic behavior of a mixed spin nanowire structure. Considering a hexagonal symmetry of the distribution of the sites, the whole lattice was interpreted as composed of two sub-lattices, a midland chain of spin-1/2 and an outer shell hexagonal of spin-1. Through the curves of the Lyapunov exponent and of the order parameters, the magnetic phase diagrams were plotted relating the magnitude of the external magnetic field with the temperature, T,hoD. For negative values of the anisotropic constant D the system showed more than one temperature of phase transition for a same magnitude of external magnetic field. This split of the phase transition branch was understood as a phase transition decoupling of the two sub-lattices. The reason for this phase transition decoupling is a competition between the states S=±1 and S=0 just in one of the sub-lattices. This behavior had not been observed in the absence of an oscillating magnetic field.

Experimental evaluation and development of predictive models for rheological behavior of aqueous Fe3O4 ferrofluid in the presence of an external magnetic field by introducing a novel grid optimization based-Kernel ridge regression supported by sensitivity analysis

In the present study, experiments are performed to determine the changes in the viscosity of water-Fe3O4 magnetic nanofluid (MNF) with shear rate, nanoparticle concentration and magnetic field (MF) induction. It was observed that as the shear rate elevates, the MNF viscosity first diminishes and then remains almost constant. Besides, the viscosity elevated with the application of the MF and its induction and also with increasing the concentration of nanoparticles. As another novelty of this research, a novel kernel based machine learning scheme namely, grid optimization based-kernel ridge regression (Grid-KRR) model was developed to accurate prediction of viscosity of water-Fe3O4 MNF based on volume fraction of nanoparticles, shear rate, and magnitude of external MF as input features. Besides, the Random forest (RF) and Gene expression programming (GEP) models were examined for validating the Grid-KRR model. The performance criteria demonstrated that the Grid-KRR outperformed the RF.

Nonreciprocal Magnetoacoustic Waves in Dipolar-Coupled Ferromagnetic Bilayers

We study the interaction of surface acoustic waves (SAWs) with spin waves (SWs) in a ${\mathrm{Co}}_{40}{\mathrm{Fe}}_{40}{\mathrm{B}}_{20}$/$\mathrm{Au}$/${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ system composed of two ferromagnetic layers separated by a nonmagnetic $\mathrm{Au}$ spacer layer. Because of interlayer magnetic dipolar coupling between the two ferromagnetic layers, a symmetric and an antisymmetric SW mode form, which both show a highly nondegenerate dispersion relation for oppositely propagating SWs. Due to magnetoacoustic SAW-SW interaction, we observe highly nonreciprocal SAW transmission in the piezoelectric-ferromagnetic hybrid device. We experimentally and theoretically characterize the magnetoacoustic wave propagation as a function of frequency, wave vector, and external magnetic field magnitude and orientation. Additionally, we demonstrate that the nonreciprocal SW dispersion of a coupled magnetic bilayer is highly tuneable and not limited to ultrathin magnetic films, in contrast to the nonreciprocity induced by the interfacial Dzyaloshinskii-Moriya interaction. Therefore, magnetoacoustic coupling in ferromagnetic multilayers provides a promising route towards building efficient acoustic isolators.

Effects of loading rate, applied shear strain, and magnetic field on stress relaxation behavior of anisotropic magnetorheological elastomer

Experimental research and numerical computation of stress relaxation behavior of an anisotropic magnetorheological elastomer (MRE) have been conducted in this paper. The anisotropic MRE has been formed from silicone matrix and micro-sized carbonyl iron particles under a magnetic field. Stress relaxation response of the anisotropic MRE was examined by single- and multi-step relaxation tests in shear mode using double-lap shear specimens. The effects of loading rate, applied constant strain, and external magnetic field on the stress relaxation behavior of the anisotropic MRE were studied. Experimental results showed that the stress relaxation of the anisotropic MRE was slightly dependent on the loading rate, but strongly depended on the constant strain level and the magnitude of external magnetic field. When increasing the constant strain level the shear stress of the anisotropic MRE in the single-step relaxation enhanced, while the relaxation modulus declined. The shear stress and modulus of the anisotropic MRE in the relaxation periods increased with increasing the magnetic field intensity. The four-parameter fractional derivative Zener model was used to describe the stress relaxation behavior of the anisotropic MRE. The presented model was fitted well to experimental data of the anisotropic MRE in both single- and multi-step relaxation tests. The fittings of relaxation modulus and shear stress with long-term predictions for the anisotropic MRE are in a very good agreement with the experimental ones. The maximal relative error of the fitted curves compared with measured data for both relaxation modulus and shear stress is less than 5.0%. As a result, the presented model is applicable to predict the long-term stress relaxation behavior of the anisotropic MRE.

Determination of automobile alternator faults using harmonic analysis of external magnetic field

Evaluation of the external magnetic field parameters allows determining the technical condition of the automobile alternator with minimum labour intensity and sufficient informativity. However, measurement of the external magnetic field magnitude with Hall sensor doesn’t allow expressly recognizing an occurring fault. It has been established that the spectral decomposition of external magnetic field oscillogram significantly increases informativity of this diagnostic parameter. Indicating harmonics, which extreme value allows identifying the technical condition of the automobile alternator, are distinguished. The article materials can be used for further development and implementation of the automobile alternator diagnostics based on the parameters of the external magnetic field.

Reversible tuning of omnidirectional band gaps in two-dimensional magnonic crystals by magnetic field and in-plane squeezing

By means of the plane wave method, we study nonuniform, i.e., mode- and k-dependent, effects in the spin-wave spectrum of a two-dimensional bicomponent magnonic crystal. We use the crystal based on a hexagonal lattice squeezed in the direction of the external magnetic field wherein the squeezing applies to the lattice and the shape of inclusions. The squeezing changes both the demagnetizing field and the spatial confinement of the excitation, which may lead to the occurrence of an omnidirectional magnonic band gaps. In particular, we study the role played by propagational effects, which allows us to explain the k-dependent softening of modes. The effects we found enabled us not only to design the width and position of magnonic band gaps, but also to plan their response to a change in the external magnetic field magnitude. This allows the reversible tuning of magnonic band gaps, and it shows that the studied structures are promising candidates for designing magnonic devices that are tunable during operation.

Lattice invisibility effect based on transverse Kerker scattering in 1D metalattices

The present work proposes a novel method to achieve free phase propagation with unitary transmission efficiency, termed as lattice invisibility effects, based on transverse scattering in 1D cylindrical metalattices. Firstly, we extend Kerker conditions parity symmetry of electromagnetic modes, and a conciser scheme to eliminate both forward and backward scattering simultaneously is presented. Compared to sphere-like particles where the first four Mie modes are required, we find that transverse scattering can be realized here if only two resonances with similar parity symmetry have the same amplitude and opposite phase, because of reduced symmetry in cylindrical systems. Further, we generalize this concept to metalattices and propose an explicit principle to realize lattice transparency, as long as all the modes with similar parity profiles interfere destructively. The proof-of-concept demonstrations have been manifested by exciting pure degraded electric dipoles or co-exciting magnetic dipole and electric quadrupoles using SiO2@InSb or Si@InSb cylinders, respectively. Besides, the invisibility performance can be flexibly tuned by changing either the period of metalattices or the magnitude of external magnetic field. The revealed mechanisms will inspire more comprehensive study of directional scattering and free phase propagation, which can also potentially stimulate several advanced applications like optical cloaking, nanophotonic circuits, etc.

Twin-enhanced magnetic torque

Magnetic shape memory alloys experience magnetic-field-induced torque due to magnetocrystalline anisotropy and shape anisotropy. In a homogeneous magnetic field, torque results in bending of long samples. This study investigates the torque on a single crystal of Ni-Mn-Ga magnetic shape memory alloy constrained with respect to bending in an external magnetic field. The dependence of the torque on external magnetic field magnitude, strain, and twin boundary structure was studied experimentally and with computer simulations. With increasing magnetic field, the torque increased until it reached a maximum near 700 mT. Above 200 mT, the torque was not symmetric about the equilibrium orientation for a sample with one twin boundary. The torque on two specimen with equal strain but different twin boundary structures varied systematically with the spatial arrangement of crystallographic twins. Numerical simulations show that twin boundaries suppress the formation of 180° domains if the direction of easy magnetization between two twin boundaries is parallel to a free surface and the magnetic field is perpendicular to that surface. For a particular twin microstructure, the torque decreases with increasing strain by a factor of six due to the mutual compensation of magnetocrystalline and shape anisotropy. When free rotation is suppressed such as in transducers of magneto-mechanical actuators, magnetic-field-induced torque creates strong bending forces, which may cause friction and failure under cyclic loading.

Total internal reflection effect on gyrotropic interface

This article considers the physical features of total internal reflection at gyrotropic and isotropic interfaces for two cases: electrical gyrotropy (plasma) and magnetic gyrotropy (ferrite). It is shown that the plasma magnetization may lead to the formation of the total internal reflection effect, which does not occur in isotropic plasma. The threshold values of the magnetic field, which are necessary for the total internal reflection effect, are determined. The total internal reflection effect on a ferrite-dielectric interface for waves emanating from different angles is observed in various frequency ranges and magnetization fields. The study points out the possibility of changing the total internal reflection angle value in large limits due to a change in the external magnetic field magnitude. The calculation results of the total internal reflection angle dependence on the external magnetic field magnitude are presented. The formulas are elaborated for calculating the total internal reflection angles of different interfaces for gyrotropic and isotropic media. The generalized formulas are defined for calculating the Doppler effect in the gyrotropic media. The study demonstrates how the velocity of the media interface affects the limiting angle of total internal refection.

Study of diffusion influence on plasma channel while transporting a low-energy high intensity electron beam in the low pressure gas

This work studies the mathematical model of plasma channel. We consider the beam current in the range of 100-400 A and the external magnetic field in the range of 100-1500 G. It is shown that plasma channel expands under the influence of diffusion. The channel expansion is inversely proportional to the external magnetic field magnitude.

Controllable optical activity of non-spherical Ag and Co SERS substrate with different magnetic field**Project supported by the Key Science and Technology Research Project of Henan Province, China (Grant No. 162102210164), the Natural Science Foundation of Henan Educational Committee, China (Grant No. 17A140002), the National Natural Science Foundations of China (Grant Nos. 11574276, 11404291, and 11604079), and the Program for Science

We experimentally fabricate a non-spherical Ag and Co surface-enhanced Raman scattering (SERS) substrate, which not only retains the metallic plasmon resonant effect, but also possesses the magnetic field controllable characteristics. Raman detections are carried out with the test crystal violet (CV) and rhodamine 6G (R6G) molecules with the initiation of different magnitudes of external magnetic field. Experimental results indicate that our prepared substrate shows a higher SERS activity and magnetic controllability, where non-spherical Ag nanoparticles are driven to aggregate effectively by the magnetized Co and plenty of hot-spots are built around the metallic Ag nanoparticles, thereby leading to the enhancement of local electromagnetic field. Moreover, when the external magnetic field is increased, our prepared substrate demonstrates excellent SERS enhancement. With the 2500 Gs and 3500 Gs (1 Gs = 10−4 T) magnetic fields, SERS signal can also be obtained with the detection limit lowering down to 10−9 M. These results indicate that our proposed magnetic field controlled substrate enables us to freely achieve the enhanced and controllable SERS effect, which can be widely used in the optical sensing, single molecule detection and bio-medical applications.

Impact of surface strain on the spin dynamics of deposited Co nanowires

Tailoring the magnetic properties at atomic-scale is essential in the engineering of modern spintronics devices. One of the main concerns in the novel nanostructured materials design is the decrease of the paid energy in the way of functioning, but allowing to switch between different magnetic states with a relative low-cost energy at the same time. Magnetic anisotropy (MA) energy defines the stability of a spin in the preferred direction and is a fundamental variable in magnetization switching processes. Transition-metal wires are known to develop large, stable spin and orbital magnetic moments together with MA energies that are orders of magnitude larger than in the corresponding solids. Different ways of controlling the MA have been exploited such as alloying, surface charging, and external electrical fields. Here we investigate from a first-principle approach together with dynamic calculations, the surface strain driven mechanism to tune the magnetic properties of deposited nanowires. We consider as a prototype system, the monoatomic Co wires deposited on strained Pt(111) and Au(111) surfaces. Our first-principles calculations reveal a monotonic increase/decrease of MA energy under compressive/tensile strain in supported Co wire. Moreover, the spin dynamics studies based on solving the Landau-Lifshitz-Gilbert equation show that the induced surface-strain leads to a substantial decrease of the required external magnetic field magnitude for magnetization switching in Co wire.

Optical response in a laser-driven quantum pseudodot system

We investigate theoretically the intense laser-induced optical absorption coefficients and refractive index changes in a two-dimensional quantum pseudodot system under an uniform magnetic field. The effects of non-resonant, monochromatic intense laser field upon the system are treated within the framework of high-frequency Floquet approach in which the system is supposed to be governed by a laser-dressed potential. Linear and nonlinear absorption coefficients and relative changes in the refractive index are obtained by means of the compact-density matrix approach and iterative method. The results of numerical calculations for a typical GaAs quantum dot reveal that the optical response depends strongly on the magnitude of external magnetic field and characteristic parameters of the confinement potential. Moreover, we have demonstrated that the intense laser field modifies the confinement and thereby causes remarkable changes in the linear and nonlinear optical properties of the system.

Tunable and enhanced SERS activity of magneto-plasmonic Ag–Fe3O4 nanocomposites with one pot synthesize method

In this paper, we report the tunable and enhanced SERS activity of magneto-plasmonic Ag–Fe3O4 nanocomposites that are synthesized by a one pot method. Crystal violet (CV), rhodamine 6 G (R6G) and 4-mercaptobenzoic acid (4-MBA) molecules are used to investigate the SERS optical activity of Ag–Fe3O4 nanocomposites under different external magnetic fields (1500, 2000, 2500, 3500 and 5000 gauss). The experimental results demonstrate the enhanced Raman effects that can be obtained by increasing the magnitude of external magnetic field. This is because the electromagnetic hot spots located between the neighboring Ag–Fe3O4 nanocomposites can be tuned by utilizing the external magnetic field. The bigger density of the hot-spots and amplitude of the electric field in the hot-spot are responsible for the enhanced SERS effect. The detection limit of CV molecule can be at least down to 10−9 M. The spectra measurements of hemoglobin adsorbed on the Ag−Fe3O4 nanocomposites under different external magnetic fields are also performed to explore its bio-applications. Finite element method (FEM) is used to simulate the local electromagnetic field distribution in Ag–Fe3O4 nanocomposites, revealing the SERS enhanced mechanism is determined mainly by the near field enhanced electromagnetic field. Due to its tunable and enhanced properties, Ag–Fe3O4 nanocomposites are expected to be promising SERS substrates for chemical and biological sensing applications.

Negative refraction at dielectric–magnetized plasma interface

The behaviors of negative refraction of electromagnetic waves propagation at the dielectric–magnetized plasma interface are investigated in detail. The Faraday and Voigt effects on the properties of negative refraction are calculated and discussed. The results show that the behavior of negative refraction can be tuned and controlled correspondingly due to the magneto-optical effects. The properties of negative refraction behave differently in different frequency region and the magnitude of external magnetic field. Moreover, negative refraction can be realized at the dielectric–magnetized plasma interface above the plasma frequency, which is different from the case of dielectric–plasma interface.

Modeling the response of a top hat electrostatic analyzer in an external magnetic field: Experimental validation with the Juno JADE‐E sensor

AbstractWe investigate the response function of an electrostatic analyzer when electron gyroradii in a magnetic field become comparable to the scale size of the sensor. This occurs when electrons have sufficiently small energies and are in a strong magnetic field. Through simulations and laboratory experiments with the Jovian Auroral Distribution Experiment‐Electron (JADE‐E) sensor, we observe the energy response, detection angle distribution, and geometric factor to change significantly. Using electro‐optics simulation results, we develop semiempirical and empirical relationships that can be used for top hat electrostatic analyzers. We present a model based on these relationships that covers an energy range between 0.1 keV and 5 keV with a uniform external magnetic field magnitude between 0–3 G and verified that these relationships apply to JADE‐E in a specially designed testing environment by comparing with the model. We find that the model agrees well with the JADE‐E sensor validating it for top hat electrostatic analyzers more generally.

Magnetically controlled planar hyperbolic metamaterials for subwavelength resolution.

Breaking diffraction limitation is one of the most important issues and still remains to be solved for the demand of high-density optoelectronic components, especially for the photolithography industry. Since the scattered signals of fine feature (i.e. the size is smaller than half of the illuminating wavelength λ) are evanescent, these signals cannot be captured by using conventional glass- or plastic-based optical lens. Hence the corresponding fine feature is lost. In this work, we propose and analyze a magnetically controlled InSb-dielectric multi-layered structure with ability of subwavelength resolution at THz region. This layered structure can resolve subwavelength structures at different frequencies merely changing the magnitude of external magnetic field. Furthermore, the resolving power for a fixed incident frequency can be increased by only increasing the magnitude of applied external magnetic field. By using transfer matrix method and effective medium approach, the mechanism of achieving super resolution is elucidated. The electromagnetic numerical simulation results also prove the rationality and feasibility of the proposed design. Because the proposed device can be dynamically reconfigured by simply changing the magnitude of external magnetic field, it would provide a practical route for multi-functional material, real-time super-resolution imaging, and photolithography.