Magnetic Field Coupling Research Articles

Control the collective behaviors in a functional neural network

Specific biophysical neurons are presented to detect different stimuli, and these external exciting signals are encoded to trigger appropriate firing modes and action potentials for signal propagation between neurons in the network. A thermosensitive neuron can estimate the effect of temperature changes on the excitability and firing modes in nervous system, a photocurrent-dependent neuron can be sensitive to the changes of external illumination or light, and an auditory neuron can perceive acoustic wave when the vibration energy is absorbed and converted into field energy in the loop of neural circuits. From biophysical viewpoint, some specific electric components such as thermistor, phototube, and piezoelectric ceramics can be incorporated into neural circuits for activating specific functions, and thus the external stimuli such as heat, light and vibration can be detected because these energy injections can be converted to intrinsic field energy in the neural circuits. In this paper, three kinds of different neural circuits are coupled in a close loop, energy pumping and the stability of phase synchronization are investigated by regulating the properties of coupling channels, furthermore, the noise effect is also estimated. When induction coil is used to couple the neural circuits, phase stability is controlled under magnetic field coupling, and the activation of noise can change the stability of phase synchronization. The intrinsic field energy in the light-dependent neuron is increased with the increase of coupling intensity when voltage coupling via resistor and magnetic field coupling via induction coil are switched on. In case of electric field coupling via capacitor, the energy in the light-dependent neural circuit keeps oscillatory with small amplitude. These results indicate that magnetic field can be the most suitable way for realizing synchronous information encoding between different functional neurons than the electric synapse coupling because continuous pumping of ions can induce magnetic field in the cell, and all the neurons are controlled completely by effective pumping in field energy.

Design of W-band PIN Diode SPDT Switch with Low Loss

A W-band PIN diode single pole double throw (SPDT) switch with low insertion loss (IL) was successfully developed using a hybrid integration circuit (HIC) of microstrip and coplanar waveguide (CPW) in this paper. In order to achieve low loss of the SPDT switch, the beam-lead PIN diode 3D simulation model was accurately established in Ansys High Frequency Structure Simulator (HFSS) and the W-band H-plane waveguide-microstrip transition was realized based on the principle of the magnetic field coupling. The key of the proposed method is to design the H-plane waveguide-microstrip transition, it not only realizes the low IL of the SPDT switch, but also the direct current (DC) bias of the PIN diode can be better grounded. In order to validate the proposed design method, a W-band PIN diode SPDT switch is fabricated and measured. The measurement results show that the IL of the SPDT switch is less than 2 dB in the frequency range of 85 to 95 GHz, while the isolation of the SPDT switch is greater than 15 dB in the frequency range of 89.5 to 94 GHz. In the frequency range of 92 to 93 GHz, the IL of the SPDT switch is less than 1.65 dB, and its isolation is higher than 22 dB. Switch rise time and switch fall time of the SPDT switch are smaller than 29ns and 19ns, respectively. Good agreement between the simulations and measurements validates the design method.

Hyperfine-mediated transitions between electronic spin-1/2 levels of transition metal defects in SiC

Transition metal defects in SiC give rise to localized electronic states that can be optically addressed in the telecom range in an industrially mature semiconductor platform. This has led to intense scrutiny of the spin and optical properties of these defect centers. For spin-1/2 defects, a combination of the defect symmetry and the strong spin–orbit coupling may restrict the allowed spin transitions, giving rise to defect spins that are long lived, but hard to address via microwave spin manipulation. Here, we show via analytical and numerical results that the presence of a central nuclear spin can lead to a non-trivial mixing of electronic spin states, while preserving the defect symmetry. The interplay between a small applied magnetic field and hyperfine coupling opens up magnetic microwave transitions that are forbidden in the absence of hyperfine coupling, enabling efficient manipulation of the electronic spin. We also find that an electric microwave field parallel to the c-axis can be used to manipulate the electronic spin via modulation of the relative strength of the dipolar hyperfine term.

Electric field control of the reversible magnetocaloric effect in strain-mediated Ni37.5Co12.5Mn35Ti15/PMN-PT composite

In this study, the martensite transformation of Ni37.5Co12.5Mn35Ti15 ribbon was studied and regulated by the electric field-induced strain in the PMN-PT substrate. The reversible magnetocaloric effect in the Ni37.5Co12.5Mn35Ti15/PMN-PT composite was enhanced by manipulating transition paths under the coupling of magnetic field and electric field, which is significantly important for applications in solid-state refrigeration. With the assistance of E = +8 kV/cm, the reversible entropy change increased from 19.5 to 25.7 J/kgK at 294.5 K. Meanwhile, the reversible cooling temperature span was also enlarged. Hence, the reversible refrigerant capacity was enhanced from 83 to 131 J/kg, and the increase ratio reached 58%. On this basis, an active magnetic regenerating cycle facilitated by an electric field was designed. This work provides an effective method for enhancing reversible caloric effects in first-order phase transition materials via electric fields.

Large exchange bias and low-temperature glassy state in the frustrated triangular-lattice antiferromagnetBa3NiIr2O9

Here, we report both ac and dc magnetization, thermodynamic and electric properties of hexagonal Ba$_3$NiIr$_2$O$_9$. The Ni$^{2+}$ (spin-1) forms layered triangular-lattice and interacts antiferromagnetically while Ir$^{5+}$ is believed to act as magnetic link between the layers. This complex magnetic interaction results in magnetic frustration leading to a spin-glass transition at $T_f$ $\sim$ 8.5 K. The observed magnetic relaxation and aging effect also confirms the nonequilibrium ground state. The system further shows large exchange bias which is tunable with cooling field. Below the Curie-Weiss temperature $\theta_{CW}$ ($\sim$ -29 K), the magnetic specific heat $C_m$ displays a broad hump and at low temperature follows $C_m = \gamma T^\alpha$ dependence where both $\gamma$ and $\alpha$ show dependence on temperature and magnetic field. A sign change in magnetoresistace is observed which is due to an interplay among magnetic moment, field and spin-orbit coupling.

Generalized Rashba Coupling Approximation to a Resonant Spin Hall Effect of the Spin–Orbit Coupling System in a Magnetic FieldSupported by the National Natural Science Foundation of China (Grant Nos. 12075040, 11875231, 11974064, and 12047564), and the Chongqing Research Program of Basic Research and Frontier Technology (Grant No. cstc2020jcyj-msxmX0890).

We introduce a generalized Rashba coupling approximation to analytically solve confined two-dimensional electron systems with both the Rashba and Dresselhaus spin–orbit couplings in an external magnetic field. A solvable Hamiltonian is obtained by performing a simple change of basis, which has the same form as that with only Rashba coupling. Each Landau state becomes a new displaced-Fock state instead of the original Harmonic oscillator Fock state. Analytical energies are consistent with the numerical ones in a wide range of coupling strength even for a strong Zeeman splitting, exhibiting the validity of the analytical approximation. By using the eigenstates, spin polarization correctly displays a jump at the energy-level crossing point, where the corresponding spin conductance exhibits a pronounced resonant peak. As the component of the Dresselhaus coupling increases, the resonant point shifts to a smaller value of the magnetic field. In contrast to pure Rashba couplings, we find that the Dresselhaus coupling and Zeeman splittings tend to suppress the resonant spin Hall effect. Our method provides an easy-to-implement analytical treatment to two-dimensional electron gas systems with both types of spin–orbit couplings by applying a magnetic field.

A piezoelectric wind energy harvester excited indirectly by a coupler via magnetic-field coupling

Energy harvesting from wind-induced vibration energy using piezoelectric materials has received great attention because of the self-powered demand for wireless sensor networks. To improve the reliability, output performance and environmental adaptability (or designability of the structure), a piezoelectric wind energy harvester excited indirectly by a coupler via magnetic-field coupling (MC-PWEH) is proposed in this paper. The MC-PWEH is mainly composed of a piezoelectric transducer and a coupler consisting of a flexible beam, a cylinder, some exciting magnets and added coupler mass. By introducing the interaction of the piezoelectric transducer sealed in the chamber and the cylinder via the magnetic coupling, the interactive vortex-induced vibration (VIV) and galloping is realized and the composite vibration energy is transformed into electric energy. The feasibility of the structure and principle of the MC-PWEH is proved through theoretical simulations and experiments. The results indicated that the piezoelectric transducer began to oscillate strongly and generate fairly high output voltage when the wind speed exceeded a low critical wind speed, accompanied by a coupling phenomenon of VIV and galloping, and then finally converged to a stable value when the wind speed exceeded a high critical value. Moreover, the critical wind speeds, bandwidth of wind speed, natural frequency and power generation performance of the MC-PWEH could be adjusted by changing the structural parameters. Under the transducer proof mass of 50 g, the optimal wind speed bandwidth for the MC-PWEH to output voltage greater than 3.5 V obtained was 25.84 m⋅s−1 that occupies 86.12% of the experimental wind speed bandwidth. The achieved maximum output power was 4.73 mW at the optimal external load resistance of 1000 kΩ and wind speed of 24 m⋅s−1.

Effect of magnetic fields on the shot noise of a quantum dot with Luttinger leads

We study the shot noise of a strongly correlated quantum dot system in the Kondo regime, concentrating on the joint effect of a magnetic field B and intralead Coulomb interaction. A shot noise formula is derived. The shot noise is suppressed by the magnetic field when the intralead interaction is weak, but improved by the field when the interaction is strong. The differential shot noise has a peak or valley at eV = ±gμBB for weak or moderately strong intralead interaction. As the interactions increase, these singular behaviours gradually disappear. In the strong interaction limit, the shot noise's curve has a power-law dependence on the voltage. The intralead Coulomb interaction also modulates the Fano line shape of shot noise. The Fano factor is enhanced by the magnetic field and dot-lead asymmetric coupling and is always sub-Poissonian noise.

Spin structure factors of doped monolayer Germanene in the presence of spin-orbit coupling

In this paper, we present a Kane-Mele model in the presence of magnetic field and next nearest neighbors hopping amplitudes for investigations of the spin susceptibilities of Germanene layer. Green’s function approach has been implemented to find the behavior of dynamical spin susceptibilities of Germanene layer within linear response theoryand in the presence of magnetic field and spin-orbit coupling at finite temperature. Our results show the magnetic excitation mode for both longitudinal and transverse components of spin tends to higher frequencies with spin-orbit coupling strength. Moreover the frequency positions of sharp peaks in longitudinal dynamical spin susceptibility are not affected by variation of magnetic field while the peaks in transverse dynamical susceptibility moves to lower frequencies with magnetic field. The effects of electron doping on frequency behaviors of spin susceptibilities have been addressed in details. Finally the temperature dependence of static spin structure factors due to the effects of spin-orbit coupling, magnetic field and chemical potential has been studied.

Dzyaloshinskii Interaction and Exchange-Relativistic Effects in Orthoferrites

We present an overview of the microscopic theory of the Dzyaloshinskii-Moriya (DM) coupling and related exchange-relativistic effects such as exchange anisotropy, electron-nuclear antisymmetric supertransferred hyperfine interactions, antisymmetric magnetogyrotropic effects, and antisymmetric magnetoelectric coupling in strongly correlated 3$d$ compounds focusing on orthoferrites RFeO$_3$ (R is a rare-earth ion or yttrium Y). % Particular emphasis will be placed on the role of crystal field effects, the sense and direction of the Dzyaloshinskii vector, its dependence on the superexchange bonding geometry, and other subtle features of exchange-relativistic effects. Most attention in the paper centers around the derivation of the Dzyaloshinskii vector, its value, orientation, and sense (sign) under different types of the (super)exchange interaction and crystal field. Microscopically derived expression for the dependence of the Dzyaloshinskii vector on the superexchange geometry allows one to find all the overt and hidden canting angles in orthoferrites RFeO$_3$ as well as corresponding contribution to magnetic anisotropy. Being based on the theoretical predictions regarding the sign of the Dzyaloshinskii vector we have predicted and study in detail a novel magnetic phenomenon, {\it weak ferrimagnetism} in mixed weak ferromagnets with competing signs of the Dzyaloshinskii vectors. The ligand NMR measurements in weak ferromagnets are shown to be an effective tool to inspect the effects of DM coupling in an external magnetic field. Along with orthoferrites RFeO$_3$ and weak ferrimagnets RFe$_{1-x}$Cr$_x$O$_3$, although to a lesser extent, we address such typical weak ferromagnets as $\alpha$-Fe$_2$O$_3$, FeBO$_3$, and FeF$_3$.

Tuning electronic transport through magnetic field and magnetoelectric coupling of multiferroic nanocomposites

Detailed analysis on structural, dielectric and ac electrical transport with dc magnetic field variation and magnetoelectric response are studied on semiconductor based multiferroic La0.7Sr0.3MnO3 - ZnO nanocomposites. The impedance data is observed to gradually enhance with magnetic field due to the strain developed in the sample, hampering the charge flow in the system. The nanocomposites display prominent magneto-impedance (∼87%) and magnetodielectric (∼35%) at room temperature. Nyquist plots are fitted utilizing two resistance-capacitor parallel circuits at varying magnetic fields demonstrating the governing role of La0.7Sr0.3MnO3 and ZnO grain boundaries. The grain boundary resistance of La0.7Sr0.3MnO3 decreases with field due to the depinning of domain walls from the grain boundary pinning centers and therefore improving the spin dependent transport mechanism while the grain boundary resistance of ZnO increases with field due to the scattering of the charge carrier. The magnetoelectric coupling investigated at a frequency of 1 kHz is accomplished in both longitudinal and transverse mode. Further, the magnetoelectric voltage induced by ac magnetic field executes a linear magnetoelectric response. The viewed magnetoelectric coupling might be in consequence of the field influenced magnetostriction of the piezomagnetic element of the composites. Such multiferroic material with tuning ac electrical property with magnetic field alongside magnetoelectric response can be pertinent in future solid-state microelectronic devices and sensor applications.

Selective spin transmission through a driven quantum system: A new prescription

Several proposals are available to get selective spin transmission through different nano-junctions and in all the cases the regulation is done either by applying a magnetic field or by tuning spin–orbit (SO) coupling. In the present work, we explore a separate scheme where the spin-dependent transport is regulated externally by irradiating a quantum ring that bridges the contact electrodes. This is a new proposal of generating spin selective transmission through a nano-junction, to the best of our knowledge. A high degree of spin polarization along with its phase alteration can be achieved by suitably adjusting the irradiation, circumventing the regulation of magnetic field and/or SO coupling. The effect of irradiation is included through the well-known Floquet-Bloch ansatz, where all the spin-dependent transport phenomena are worked out using Green’s function formalism following the Landauer–Büttiker prescription within a tight-binding framework. Precise dependencies of light irradiation, SO coupling, magnetic flux threaded by the ring, interface sensitivity, system temperature, and impurities on spin polarization are critically investigated. Our analysis may give a new platform for spin selective electron transmission and make it applicable to other complex nano-structured materials also. We strongly believe that the present proposal can be examined in a suitable laboratory.

Comparative performance analysis of bearingless switched reluctance motor

To solve the magnetic field coupling problem in the traditional bearingless permanent-magnet motor, which has magnets on the rotor, we propose two topologies of bearingless switched reluctance motors (BLSRMs) with magnets on the stator yoke. The first is a six/four-pole BLSRM with three pairs of permanent magnets on the stator and the second is a six/four-pole BLSRM with one pair of stator yoke magnets. First, the working principle of BLSRMs is introduced, including the structure and winding configuration, and the mechanism of generating levitation force is analyzed in detail. Based on 2D finite element analysis, the electromagnetic characteristics of the prototype are compared, including torque, suspension force, no-load back EMF, and no-load permanent magnet linkage. The calculation results show that at high speeds, the coupling between the levitation force winding and the torque winding of the BLSRM with one magnet pair is low, which allows for better decoupling performance and greater levitation force. In addition, although the motor with three pairs of permanent magnets in the stator yoke shows better torque performance, the loss of the motor is higher at a high speed. The research results lay a theoretical foundation for further research on a new type of bearingless motors.

Ionization degree and magnetic diffusivity in star-forming clouds with different metallicities

ABSTRACT Magnetic fields play such essential roles in star formation as transporting angular momentum and driving outflows from a star-forming cloud, thereby controlling the formation efficiency of a circumstellar disc and also multiple stellar systems. The coupling of magnetic fields to the gas depends on its ionization degree. We calculate the temperature evolution and ionization degree of a cloud for various metallicities of Z/Z⊙ = 10−6, 10−5, 10−4, 10−3, 10−2, 10−1, and 1. We update the chemical network by reversing all the gas-phase processes and by considering grain-surface chemistry, including grain evaporation, thermal ionization of alkali metals, and thermionic emission from grains. The ionization degree at nH ∼ 1015–1019 cm−3 becomes up to eight orders of magnitude higher than that obtained in the previous model, owing to the thermionic emission and thermal ionization of K and Na, which have been neglected so far. Although magnetic fields dissipate owing to ambipolar diffusion or Ohmic loss at nH < 1015 cm−3, the fields recover strong coupling to the gas at nH ∼ 1015 cm−3, which is lower by a few orders of magnitude compared to the previous work. We develop a reduced chemical network by choosing processes relevant to major coolants and charged species. The reduced network consists of 104 (161) reactions among 28 (38) species in the absence (presence, respectively) of ionization sources. The reduced model includes H2 and HD formation on grain surfaces as well as the depletion of O, C, OH, CO, and H2O on grain surfaces.

Effects of spin-orbit coupling and magnetic field on electronic properties of Germanene structure

In this paper, we present a Kane-Mele model in the presence of magnetic field and next nearest neighbors hopping amplitudes for investigations the electronic and optical properties of monolayer Germanene. Specially, we address the dynamical conductivity of the structure as a function of photon frequency and in the presence of magnetic field and spin-orbit coupling at finite temperature. Using linear response theory and Green’s function approach, the frequency dependence of optical conductivity has been obtained in the context of Kane-Mele model Hamiltonian. Our results show a finite Drude response at low frequency at non zero value for magnetic field in the presence of spin-orbit coupling. However Drude weight gets remarkable amount in the presence of electron doping. The thermal conductivity and specific heat increase with increasing the temperature at low amounts of temperature due to the increasing of thermal energy of charge carriers and excitation of them to the conduction bands. The results for Seebeck coefficient show the sign of thermopower is negative in the presence of spin-orbit coupling. Also we have studied the temperature dependence of electrical conductivity of Germanene monolayer due to both spin orbit coupling and magnetic field factors in details.

An Optically Aided Magnetic Tracking Approach for Magnetically Actuated Capsule Robot

Embedded with an internal permanent magnet (IPM), a magnetically actuated capsule (MAC) robot can be controlled inside gastrointestinal (GI) tract by an external permanent magnet (EPM) outside of human body. Locomotion control of MAC robot can be achieved based on precise pose feedback that is usually carried out by magnetic tracking. However, the coupling of internal and external magnetic fields will deteriorate the accuracy. To solve this problem, we propose a novel optical-magnetic fusion tracking framework in this article, which can be applied to track the MAC robot in real time. The proposed method utilizes the prior-known pose of EPM estimated from the optical tracking method to decouple IPM’s magnetic field from the composite magnetic field to achieve higher tracking accuracy of wireless capsule endoscopy (WCE). Moreover, magnetic field methods have been analyzed to validate the accuracy of theoretical description of magnetic field. The proposed strategy is validated by both static and dynamic experiments. The average position and orientation errors are 2.6 mm and 1.54°, respectively.

An Ultrawideband Magnetic Probe With High Electric Field Suppression Ratio

In this article, an ultrawideband magnetic probe with high electric field suppression ratio (EFSR) is proposed. The probe has three parts: the loop part, the transmission part, and the head part. Shield metal sheets are designed in the loop part to enhance EFSR. The tapered transmission line in the transmission part and the quasi coaxial transition in the head part are adopted for impedance matching between the induction loop and the grounded coplanar waveguide (GCPW) in the head part. Then, segmented resistance–inductance–capacitance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> ) equivalent circuit models of the probe are proposed for magnetic field coupling and electric field coupling, which are suitable for accurate modeling and efficient optimization of the magnetic probe. In addition, the coupling capacitors between the shield metal sheets and the device under test (DUT) are extracted utilizing the conformal transforming method with analytical formulas. Finally, this magnetic probe is fabricated under printed circuit board (PCB) technology and used in measuring the magnetic field distribution. The measurement and simulation results agree well. The probe has a bandwidth of 100 MHz–30 GHz and an EFSR of higher than 21 dB. Compared with the conventional probe with similar bandwidth, the proposed probe can improve the EFSR by 9 dB.

Magnetic field coupling microfluidic synthesis of diluted magnetic semiconductor quantum dots: the case of Co doping ZnSe quantum dots

Magnetic field coupling microfluidic synthesis of ZnCoSe QDs. The particle size and doping amount of QDs can be adjusted by adjusting the applied field, thereby realizing online control of the magnetic and optical properties of QDs.

Anti-plane fracture problem of three nano-cracks emanating from a magnetoelectrically permeable regular triangle nano-hole in magnetoelectroelastic materials

Based on the Gurtin–Murdoch surface/interface model and complex potential theory, by constructing a new conformal mapping, the anti-plane fracture problem of three nano-cracks emanating from a magnetoelectrically permeable triangle nano-hole in magnetoelectroelastic materials with surface effect is studied. The exact solutions of the stress intensity factor, the electric displacement intensity factor, the magnetic induction intensity factor, and the energy release rate are obtained under the boundary conditions of magnetoelectrically permeable and impermeable. The numerical examples show the influence of surface effect on the stress intensity factor, the electric displacement intensity factor, the magnetic induction intensity factor, and the energy release rate under two different boundary conditions. It can be seen that the surface effect leads to the coupling of stress, electric and magnetic field, and with the increase of cavity size, the influence of surface effect begins to decrease until it tends to classical elasticity theory.

Terahertz response of plasmonic nanoparticles: Plasmonic Zeeman Effect.

Magnetoplasmons are the coupling of an external magnetic field and a plasmon or a localized plasmon, in the case of nanoparticles. We present a theoretical study, in the quasi-static limit, of the plasmonic response of nanoparticles when a constant magnetic field is applied. The plasmonic modes split into two satellite peaks with a frequency shift proportional to the magnetic field. The constant of proportionality is the effective Bohr magneton. This splitting of the fundamental plasmonic mode is akin to the splitting of energy levels in the Zeeman effect. The results are valid for any material that has a plasmonic response. For higher magnetic fields, the frequency shift of the splitting becomes non-linear with the magnetic field as what happens with the non-linear Zeeman effect.