Additional Magnetic Field Research Articles

Cone-Shell Quantum Structures in Electric and Magnetic Fields as Switchable Traps for Photoexcited Charge Carriers.

The optical emission of cone-shell quantum structures (CSQS) under vertical electric (F) and magnetic (B) fields is studied by means of simulations. A CSQS has a unique shape, where an electric field induces the transformation of the hole probability density from a disk into a quantum-ring with a tunable radius. The present study addresses the influence of an additional magnetic field. A common description for the influence of a B-field on charge carriers confined in a quantum dot is the Fock-Darwin model, which introduces the angular momentum quantum number l to describe the splitting of the energy levels. For a CSQS with the hole in the quantum ring state, the present simulations demonstrate a B-dependence of the hole energy which substantially deviates from the prediction of the Fock-Darwin model. In particular, the energy of exited states with a hole lh> 0 can become lower than the ground state energy with lh= 0. Because for the lowest-energy state the electron le is always zero, states with lh> 0 are optically dark due to selection rules. This allows switching from a bright state (lh= 0) to a dark state (lh> 0) or vice versa by changing the strength of the F or B field. This effect can be very interesting for trapping photoexcited charge carriers for a desired time. Furthermore, the influence of the CSQS shape on the fields required for the bright to dark state transition is investigated.

Soliton molecules and their scattering by a localized P T-symmetric potential in atomic gases.

We propose a physical scheme to study the formation of optical soliton molecules (SMs), consisting of two solitons bound together with a π-phase difference, and the scattering of SMs by a localized parity-time (P T)-symmetric potential. In order to stabilize SMs, we apply an additional space-dependent magnetic field to introduce a harmonic trapping potential for the two solitons and balance the repulse interaction induced by the π-phase difference between them. On the other hand, a localized complex optical potential obeying P T symmetry can be created through an incoherent pumping and spatial modulation of the control laser field. We investigate the scattering of optical SMs by the localized P T-symmetric potential, which exhibits evident asymmetric behavior and can be actively controlled by changing the incident velocity of SMs. Moreover, the P T symmetry of the localized potential, together with the interaction between two solitons of the SM, can also have a significant effect on the SM scattering behavior. The results presented here may be useful for understanding the unique properties of SMs and have potential applications in optical information processing and transmission.

Negative muon spin rotation and relaxation on superconducting MgB2

The internal nuclear magnetic field in a superconducting MgB2 powder sample was studied with a µ− SR technique. Although the past µ +SR study on MgB2 reported the appearance of a dynamic behavior even below Tc due to µ + diffusion, µ− SR shows a static behavior in the whole temperature range measured, as expected. The ZF-µ− SR spectra do not suggest any appearance of additional magnetic field below Tc within the experimental accuracy. Considering the small asymmetry of the µ− SR signal, it is a challenge to detect the appearance of an internal magnetic field below Tc caused by the time reversal symmetry breaking.

Testing and Analysis Method of Low Remanence Materials for Magnetic Shielding Device.

Magnetic shielding devices with a grid structure of multiple layers of highly magnetically permeable materials (such as permalloy) can achieve remanent magnetic fields at the nanotesla (nT) level or even lower. The remanence of the material inside the magnetic shield, such as the building materials used in the support structure, can cause serious damage to the internal remanence of the magnetic shield. Therefore, it is of great significance to detect the remanence of the materials used inside the magnetic shielding device. The existing test methods do not limit the test environment, the test process is vulnerable to additional magnetic field interference and did not consider the real results of the material in the weak magnetic environment. In this paper, a novel method of measuring the remanence of materials in a magnetic shielding cylinder is proposed, which prevents the interference of the earth's magnetic field and reduces the measurement error. This method is used to test concrete components, composite materials and metal materials commonly applicated in magnetic shielding devices and determine the materials that can be used for magnetic shielding devices with 1 nT, 10 nT and 100 nT as residual magnetic field targets.

Key performance of tunneling magnetoresistance sensing unit modulated by exchange bias of free layer

Optimizing sample structural parameters, magnetic field annealing, series-parallel bridge design, current thermal effect, and additional bias magnetic field are common methods used for controlling the tunneling magnetoresistance (TMR) magnetic sensing performance. By employing these methods, key performance parameters of TMR sensors such as sensitivity, noise resistance index, linearity, and linear magnetic field range can be optimized and improved. Changing the sample structural parameters, such as the pinning layer, free layer, and barrier layer materials and thickness of the TMR magnetic sensing unit, can change the exchange bias field and thus enhance the TMR magnetic sensing performance parameters. In this study, through micromagnetic simulation and experimental measurements, it is discovered that by modifying the exchange coupling in the free layer CoFeB/Ru/NiFe/IrMn, the exchange bias field magnitude of the TMR free layer can be modulated, leading to improved performance of the TMR magnetic sensing unit. As the IrMn pinning effect is gradually enhanced, the linear magnetic field range of the TMR magnetic sensing unit increases, but the magnetic field sensitivity decreases. It is further found that the linearity of the TMR magnetic sensor is optimal within a range of ±0.5 times the magnetic moment variation of the free layer (primarily the CoFeB layer). Through our work, the effect of exchange bias field (caused by the pinning IrMn of the free layer) on the magnetic sensing performance is verified in the TMR magnetic sensing unit. Our work demonstrates more possibilities for designing and optimizing TMR magnetic sensors, enriching the dimensions of magnetic sensing performance modulation.

Simultaneous in-situ compensation method of residual magnetic fields for the dual-beam SERF atomic magnetometer

Near-zero magnetic field condition is essential to keep the spin-exchange relaxation-free (SERF) regime for the atomic magnetometer. We analyzed the output response variations of the dual-beam SERF magnetometer under different DC residual magnetic fields. Considering the problem that the gradient coil may introduce an additional DC magnetic field when compensating the gradient field, we propose a novel method of simultaneous in-situ compensation of gradient and DC residual magnetic field with high precision. The sensitivity and effectiveness of the compensation method for residual magnetic fields under 1 nT were verified by simulation and experiment. The precision of the gradient residual magnetic field compensation is better than 2 pT/mm. We built a dual-beam SERF atomic magnetometer platform to validate the proposed method. The magnetic field measurement sensitivity is 7 fT/Hz1/2 after residual magnetic fields compensation by the method mentioned in this paper, which is 4 times higher than the sensitivity of 36 fT/Hz1/2 without residual magnetic fields compensation.

Suppression mechanism of equilibrium magnetic islands in CFQS low-<inline-formula><tex-math id="Z-20231023161017">\begin{document}$\boldsymbol \beta$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20230546_Z-20231023161017.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20230546_Z-20231023161017.png"/></alternatives></inline-formula> plasma

Magnetic island produced in toroidal magnetic confinement plasma has a three-dimensional helical structure because of the rotational transform, especially the equilibrium magnetic surface of the stellarator is three-dimensional helical structure. Thus, the formation and instability of the magnetic island of the Stellarator is a typical issue of the three-dimensional physics and is also one of the key topics of the physics research of the Stellarator. Magnetic islands and related tearing mode physics are major issues in stellarator. The non-inductively current drive, i.e. electron cyclotron current drive (ECCD) can be used as one of the approaches to adjusting the rotational transform, and hence, affecting the generation of magnetic islands. In this study, we use an additional toroidal magnetic field to generate <i>m</i>/<i>n</i> = 5/2 magnetic islands in the low-<i>β</i> operation on the Chinese First Quasi-axisymmetric Stellarator (CFQS) so that the influence of the bootstrap current is negligible. Then, we investigate the suppression mechanism of magnetic islands in low-<i>β</i> plasma by using the HINT code. It is found that in the case of the constant current, when the current direction is positive, with the increase of current, the width of island increases. When the direction of current is reversed, the island is suppressed when the current is larger than 6 kA. The main reason is that the rotational transform is away from <i>ι</i>/2π = 0.4 rational surface and the <i>m</i>/<i>n</i>=5/2 magnetic island does not meet the resonance conditions. In the case of local current profile, the magnetic island width decreases as a result of the enhanced magnetic shear at <i>ι</i>/2π = 0.4 rational surface. Moreover, effects of the direction and the amplitude of the current on the suppression of magnetic islands are also discussed in more detail.

Spin-orbit splitting and piezoelectric properties of Janus Ge2XY (X ≠ Y = P, As, Sb and Bi).

The coexistence of spin-orbit coupling and piezoelectricity in a single material may have potential application in multifunctional devices, including spintronics, nanorobotics and piezotronics. Spin-orbit coupling provides a new means to manipulate electron's spin without an additional external magnetic field, while piezoelectricity refers to the interplay between mechanical stresses and electric polarization. Using first-principles calculations, the structural, electronic, optical, spin, and piezoelectric properties of the Janus Ge2XY (X ≠ Y = P, As, Sb, and Bi) monolayers were systematically investigated. All the Ge2XY are energetically and dynamically stable in the α phase. At the GW level, Ge2AsSb, Ge2AsBi, and Ge2SbBi have direct fundamental band gaps of 0.65, 0.64, and 0.91 eV. At the GW + BSE level, their optical gaps are 0.42, 0.45, and 0.63 eV, and the optical absorption coefficients can reach about 10-5 cm-1 in the infrared light region, which reveals that they have potential for application in infrared photodetectors. For Ge2PBi, Ge2AsBi, and Ge2SbBi containing the heavy Bi element, the lowermost conduction band and uppermost valence band have large spin splitting along the M-K and K-Γ lines, and the bands near the Fermi level possess Rashba spin splitting at the Γ point. Ge2PBi and Ge2SbBi have both large in-plane piezoelectric coefficients d11 (-0.75 and -3.18 pm V-1) and out-of-plane piezoelectric coefficients d31 (0.37 and 0.30 pm V-1). Our findings are helpful to understand the mechanism of the spin-orbit physics and piezoelectricity of Janus Ge2XY monolayers and guide experiments in exploring novel multifunctional materials.

An Enhanced Analysis of Inter-Laminar Faults in Magnetic Cores With Grain Oriented Electrical Steels for Fault Diagnosis and Condition Monitoring: Theoretical Background and Experimental Verification

Fault diagnosis and condition monitoring of electromagnetic devices are the strategies of monitoring and processing parameters of the device for fault identification and failure prediction. In this respect, core faults or inter-laminar faults (ILFs) is a key objective, with an important contribution into the whole process. This paper tends to propose a new experimental-analytical approach to fault diagnosis and condition monitoring of magnetic cores. The proposed technique is in line with the phenomenology of the magnetic hysteresis and interpreting dynamic characteristics of the magnetic cores. The distinct feature of this approach is its ability to model additional magnetic field and associated energy loss caused by ILFs. The studies were carried out on stacks of standard Epstein size strips of 3 wt % SiFe Grain Oriented (GO) steels, subjected to artificial faults. Validation of the developed approach was undertaken through experimental work and analytical modelling.

INFLUENCE OF MAGNETIC FIELD CONFIGURATION AND STRENGTH ON PLASMA PARAMETERS AND EFFICIENCY OF COATINGS DEPOSITION IN MAGNETRON SPUTTERING SYSTEM

Paper presents results of evaluation of the influence of the parameters of the additional anode electromagnetic trap for discharge electrons in a magnetron sputtering system. The efficiency of ionization processes is also investigated. It has been shown experimentally that a slight increase of the additional anode magnetic field leads to an increase of plasma density in the discharge on several times. The presence of an anode electromagnetic trap causes additional ionization zones. An increase of anode magnetic field leads to an increase of the average energy of charged discharge plasma particles. As the result, it was observed an intensification of the target material sputtering process as well as an increase of coatings deposition rate. In addition, a slight increase in the magnitude of the anode magnetic field has a positive effect on the quality and purity of the deposited coatings.

Can 1D Radiative-equilibrium Models of Faculae Be Used for Calculating Contamination of Transmission Spectra?

The reliable characterization of planetary atmospheres with transmission spectroscopy requires realistic modeling of stellar magnetic features, since features that are attributable to an exoplanet atmosphere could instead stem from the host star’s magnetic activity. Current retrieval algorithms for analyzing transmission spectra rely on intensity contrasts of magnetic features from 1D radiative–convective models. However, magnetic features, especially faculae, are not fully captured by such simplified models. Here we investigate how well such 1D models can reproduce 3D facular contrasts, taking a G2V star as an example. We employ the well-established radiative magnetohydrodynamic code MURaM to obtain three-dimensional simulations of the magnetoconvection and photosphere harboring a local small-scale dynamo. Simulations without additional vertical magnetic fields are taken to describe the quiet solar regions, while simulations with initially 100 G, 200 G, and 300 G vertical magnetic fields are used to represent facular regions of different magnetic flux density. Subsequently, the spectra emergent from the MURaM cubes are calculated with the MPS-ATLAS radiative transfer code. We find that the wavelength dependence of facular contrast from 1D radiative–convective models cannot reproduce facular contrasts obtained from 3D modeling. This has far-reaching consequences for exoplanet characterization using transmission spectroscopy, where accurate knowledge of the host star is essential for unbiased inferences of the planetary atmospheric properties.

Optimization of Process Variables for Prediction of Penetration Depth of HSLA Steel Welds Using Response Surface Methodology

The statistical model is created for predicting penetration depth in an alternating current-based additional axial magnetic field controlled shielded metal arc welding of ASTM A 516 Gr.70 steel. The design for the trials is developed using the Placket-Burman design and response surface methodology. The created model determines the optimum process variables for getting excellent penetration depth. The input variables (current, magnetic field density, and magnetic frequency) are chosen for a response like penetration depth. This model can predict the main effects and the interacting effects of three process variables. The findings reveal that a higher current value with a low magnetic field density leads to deeper penetration and vice versa. Furthermore, a greater penetration depth is achieved at lower magnetic field density and higher magnetic frequency. With a desirability of 98.8%, the optimum process variables are 110 A, 0 mT, and 60 Hz. The predicted response values produced from the regression equation based upon process variables are extremely similar to the observed output, demonstrating the usefulness of second-order regression equations. For improved joint efficiency, a high level of penetration is needed.

The multimodal motion along a solid–liquid interface of a soft microrobot driven by compound magnetic fields

In recent years, soft microrobots based on flexible materials have received increasing attention. Most of the current studies on soft microrobots have implemented only one motion mode, and because the motion environment is often set inside liquid, the strategies of multimodal motion control near the solid–liquid interface are insufficient. In this study, we present a 4 mm × 1 mm × 0.2 mm sheet-like soft microrobot bent into a ring shape and magnetized so that it can move in multiple modes along the solid–liquid interface and can be driven by different types of magnetic fields. The deformation amplitude and the total magnetic moment of the robot under the external magnetic field were obtained with the help of finite element simulations. Three different periodic magnetic field driving modes along the solid–liquid interface, namely rolling mode, walking mode, and hopping mode, were realized, and the robot’s motion speed and direction under various motion modes were adjusted by additional magnetic field strengths and magnetic field gradients. This research can enhance the adaptability of soft microrobots to various motion environments and further expand their application prospects.

A novel ultrasensitive and fast aptamer biosensor of SEB based on AuNPs-assisted metal-enhanced fluorescence

A fluorescent biosensor strategy was developed in combination with immunomagnetic separation for rapid and sensitive detection of staphylococcal enterotoxin B (SEB). Magnetic nanoparticles (MNPs) modified with aptamer of SEB could capture the SEB. Then the gold nanoparticles (AuNPs) fluorescent probe was added and a “sandwich structure” was formed between AuNPs, SEB and MNPs. The MNPs-SEB-AuNPs structure could be separated with an additional magnetic field, which resulted the lower signals of AuNPs fluorescent probe. In optimal conditions, the current method displayed a broad quantitative range from 100 to 107 fg/mL and the limit of detection was 3.43 fg/mL. The recovery of SEB-spiked milk samples ranged from 92.00 to 119.00 %, which revealed that the developed method had great accuracy. Furthermore, the method was fast and economical for ultrasensitive detection. Therefore, the fluorescent biosensor based on MNPs-AuNPs is promising for the detection of other environmental and food pollutants.

Flows of ionizing gas in the plasma accelerator channel with longitudinal magnetic field

Model and results of numerical experiments are presented for axisymmetric flows of ionizing gas in the presence of an additional longitudinal magnetic field in the channel of quasi-stationary plasma accelerator considered as perspective electric propulsion plasma engine. A two-dimensional flow model for a three-component medium consisting of atoms, ions, and electrons is based on magnetogasdynamic equations written in terms of the vector potential of magnetic field, taking into account electrical conductivity, thermal conductivity, and radiation transfer. A three-dimensional model of radiative transfer includes main mechanisms of emission and absorption for different parts of the spectrum. Numerical studies of the ionization process and radiation transfer were carried out in an approximation of local thermodynamic equilibrium. The stabilizing effect of flow rotation in the presence of a longitudinal magnetic field and thermal conductivity along the magnetic field on non-stationary unstable flows of ionizing gas, which arise at low discharge currents, is considered.

Alfvén Wave Conversion and Reflection in the Solar Chromosphere and Transition Region

Series solutions are used to explore the mode conversion of slow, Alfvén and fast magnetohydrodynamic waves injected at the base of a two-isothermal-layer stratified atmosphere with a uniform magnetic field, crudely representing the solar chromosphere and corona with intervening discontinuous transition region. This sets a baseline for understanding the ubiquitous Alfvénic waves observed in the corona, which are implicated in coronal heating and solar wind acceleration. It is found that all three injected wave types can partially transmit as coronal Alfvén waves in varying proportions dependent on frequency, magnetic field inclination, wave orientation, and distance between the Alfvén/acoustic equipartition level and the transition region. However, net Alfvénic transmission is limited for plausible parameters, and additional magnetic field structuring may be required to provide sufficient wave energy flux.

Dynamics of Electron Pearcey– Gaussian Beams in a Constant Magnetic Field

AbstractA new kind of electron Pearcey‐Gaussian beam (EPGB) with auto‐focusing properties in the presence of an additional magnetic field is introduced, which is composed of the multiplication of the Pearcey function and the Gaussian function. The closed‐form expressions of the EPGBs are obtained. Based on different initial transverse velocities, different dynamics of the EPGBs are presented. The effect of the magnetic field toward the maximum focusing plane is also demonstrated. The analytical results are in excellent agreement with direct numerical simulations.

Optimized electric heater configuration design with magnetic-field self-suppression using genetic algorithm

Atomic vapor cells are core components in various atomic sensors, and usually heated by an electric heater which would generate an additional magnetic field. To sufficiently suppress this magnetic-field interference, an optimized electric heater configuration method with magnetic-field self-suppression using a genetic algorithm is proposed. The resistance tracks in the electric heater configuration are decomposed into several heating coils; the size and current direction of each coil are optimized by the genetic algorithm to minimize the magnetic field in the heated space. The effectiveness of the proposed method is verified through the finite element simulation and an experimental test. The results show that for the optimal electric heater configuration, the average magnetic flux density introduced is approximately 2–4 times less than and dozens of times less than, respectively, the average magnetic flux density introduced in previously proposed 2 N multipole and common spiral configurations. This study is significative for electric heating with lower magnetic field and contributes to further improving the performance of atomic sensors.

Role of the chiral spin configuration in field-free spin–orbit torque-induced magnetization switching by a locally injected spin current

For deterministic magnetization switching by spin–orbit torque (SOT) in a perpendicular magnetic anisotropy system, an additional in-plane direction magnetic field is essential to break the lateral symmetry. Realizing chirality in a magnetic ordering system can be one approach for achieving asymmetry in the lateral direction for field-free magnetization switching. However, systematic analysis of the influence of the chiral spin system on deterministic switching is still scarce. We investigate the field-free SOT-induced magnetization switching by using a chiral spin configuration experimentally and theoretically with micromagnetic simulations. We designed a system in which only part of the ferromagnetic layer overlaps with the heavy metal layer in the Pt/Co/MgO structure. Therefore, a spin current exerts only on a local area of the ferromagnetic layer, which results in a Néel-type chiral spin configuration. The induced chiral spin configuration can be stabilized (or destabilized) depending on the sign of the interfacial Dzyaloshinskii–Moriya interaction and the direction of the current. The stabilized spin configuration plays a crucial role in the deterministic switching in the zero field. We expect our findings to widen the perspective on chirality-based all-electrical SOT device applications.

Electromagnetic Angular Position Sensing Using High-Magnetic-Permeability Materials

In this paper, a new electromagnetic angular position sensing method using high-magnetic-permeability metal (e.g., mu-metal) is proposed for measurement of joint angles of rotational mechanisms. An electromagnet and magnetic sensors are both located on one mechanical part and the mu-metal element is located on the other mechanical part with relative rotation to the first part around the joint. The mu-metal with high magnetic permeability is easily magnetized by the electromagnet and it exerts an additional magnetic field on the magnetic sensors dependent on the rotation angle nonlinearly. This influence is utilized for angle estimation using an extended Kalman filter. Two configurations of the angle sensing system are designed and modeled using numerical simulation. Experimental results show that the angle measurement error for both configurations is under 1% over their respective sensing range. The mu-metal based angle sensing system is also validated to be immune to ferromagnetic disturbances due to the use of an alternating magnetic field. The proposed angle sensing method is non-contacting and non-intrusive, and its off-joint configuration can measure joint angle without needing to be installed in the joint.