Magnetic Barrier Research Articles

Engineering the Spin-Orbit-Torque Efficiency and Magnetic Properties of Tb / Co Ferrimagnetic Multilayers by Stacking Order

We measure the spin-orbit torques (SOTs), current-induced switching, and domain wall (DW) motion in synthetic ferrimagnets consisting of $\mathrm{Co}$/$\mathrm{Tb}$ layers with differing stacking order grown on a $\mathrm{Pt}$ underlayer. We find that the SOTs, magnetic anisotropy, compensation temperature, and SOT-induced switching are highly sensitive to the stacking order of $\mathrm{Co}$ and $\mathrm{Tb}$ and to the element in contact with $\mathrm{Pt}$. Our study further shows that $\mathrm{Tb}$ is an efficient SOT generator when in contact with $\mathrm{Co}$, such that its position in the stack can be adjusted to generate torques additive to those generated by $\mathrm{Pt}$. With optimal stacking and layer thickness, the dampinglike SOT efficiency reaches 0.3, which is more than twice that expected from the $\mathrm{Pt}$/$\mathrm{Co}$ bilayer. Moreover, the magnetization can be easily switched by the injection of pulses with current density of about (0.5--$2)\ifmmode\times\else\texttimes\fi{}{10}^{7}\phantom{\rule{0.2em}{0ex}}\mathrm{A}/{\mathrm{cm}}^{2}$ despite the extremely high perpendicular magnetic anisotropy barrier (up to 7.8 T). Efficient switching is due to a combination of large SOTs and low saturation magnetization owing to the ferrimagnetic character of the multilayers. We observe current-driven DW motion in the absence of any external field, which is indicative of homochiral N\'eel-type DWs stabilized by the interfacial Dzyaloshinkii-Moriya interaction. These results show that the stacking order in transition metal/rare-earth synthetic ferrimagnets plays a major role in determining the magnetotransport properties relevant for spintronic applications.

Hybrid-Excited Permanent Magnet-Assisted Synchronous Reluctance Machine

This paper presents the results of simulation tests of a unique hybrid-excited permanent magnet machine operating in in different working regimes. The common feature of analyzed machine is a presence of magnetic barriers in the rotor structure. Structurally, this machine combines the advantages of the PMa-SynRM machine (Permanent Magnet-assisted Synchronous Machine) and a wound synchronous machine. The paper presents, among other results, the voltage and torque characteristics as a function of the current in the stator and the additional DC control coil. Selected results of experimental studies are also shown.

Generation of pure spin-valley beams at controllable angles by gate voltage in monolayer molybdenum disulfide

Strong spin–orbit coupling and lack of inversion symmetry in monolayer transition metal dechalcogenides has made these materials as a promising candidate for both spintronic and valleytronic applications. We investigate the effect of adjustable parameters on quantum transmission of electrons through a magnetic barrier on MoS2 monolayer and introduce selection rules for generation of perfectly polarized spin-valley beams in various directions. These selection rules provide an efficient tool for versatile electrical manipulation of spin-valley beams in two-dimensional structures.

Predicted optimization of β N limit for steady-state scenario with double transport barriers in HL-2M tokamak

The equilibria of the HL-2M tokamak, designed for steady-state operation with reversed magnetic shear and double transport barriers, are calculated using TOQ code, and the linear ideal magnetohydrodynamic (MHD) stability of the equilibria is investigated using GATO code. To improve the beta () limit, the MHD stability of the equilibria with different heights of internal transport barrier (ITB) and edge transport barrier (ETB) is simulated. The simulation results indicate that the ITB drives low globalized modes while the ETB drives high edge localized modes, and thus a moderate barrier height ratio is beneficial to MHD stability. By adjusting the heights of both barriers with different plasma shapes, as well as different locations and widths of ITBs, optimal equilibria with improved MHD stability are achieved, which always have a moderate barrier height ratio unless the ITB is extremely wide or very close to the edge. In ideal-wall conditions, when the ITB is wide enough or very close to the edge, limits could exceed six, or even reach seven in some special cases. Increasing elongation and triangularity, broadening the ITB, as well as moving the ITB to a large minor radius, can contribute to the optimization of the limit, especially when combined with the stabilizing effect from an ideal wall.

Improvement of tunneling magnetoresistance and spin-valley polarization in magnetic silicene superlattices induced by structural disorder

It is well known that the unavoidable variation of the heights and widths of the barriers (structural disorder) in semiconductor superlattices and superlattices based on two-dimensional materials degrades important physical properties such as the electronic transport and the thermoelectric response. Here, we show that the structural disorder contrary to what is expected improves the magnetoresistive and spin-valleytronic properties of magnetic silicene superlattices. We reach this conclusion by studying the impact of the random variations of the width and strength of the magnetic barriers on the tunneling magnetoresistance and spin-valley polarization. The theoretical treatment is based on a Dirac-like Hamiltonian, the transfer matrix method, and the Landauer-B\"uttiker formalism to describe silicene electrons, to obtain the transmittance, and to obtain the conductance, respectively. Our results indicate that structural disorder effects improve the magnetoresistance response and the spin-valley polarization by eliminating the conductance oscillations caused by the periodic magnetic modulation as well as by differentiating the response of the conductance for the parallel and antiparallel magnetization configuration. These results could be useful in designing versatile devices with magnetoresistive and spin-valleytronic capabilities. Particularly, magnetic silicene superlattices with moderate structural disorder are more convenient than perfect or nearly perfect ones.

The correlation between structural attributes and magnetic shielding of some metal nanoparticles engineered polymeric surfaces

Polymeric structures for use in magnetic environments are of great importance for applications ranging from simple magnetic barriers to the design of high dimensions devices, or vehicles. The damage caused by magnetic radiations is invisible, slow, and accumulative. This can lead to genetic damage, reproductive defects, cancer, neurological degeneration and nervous system dysfunction. This research work has focused on the effects of magnetic radiations onto some polymeric supports coated with different molar ratios of Zn/Al oxides and their response to magnetic radiations. Of particular interest here was the adapting the coating conditions with the magnetic barrier of the coated polymeric supports.The engineered polymeric supports have been characterized using X-ray diffraction, UV–VIS spectroscopy, SEM techniques, and magnetic measurements. The XRD and SEM results are well correlated revealing the clustering of the Zn2+ cations and the forming of ZnO nanoparticles onto the surface of the polymeric support for all used cationic ratios. The magnetic measurements proved an average magnetic nature in ZnO/AlO NPs deposited onto polymeric supports.

Multi-Objective Optimization of Interior Permanent Magnet Machine for Heavy-Duty Vehicle Direct-Drive Applications

In this paper, an interior permanent magnet (IPM) machine is presented and optimized for heavy-duty vehicle direct-drive applications. Since efficiency decrease and serious heating come along with excessive core loss under flux weakening control, a rotor topology with the combination of the eccentricity structure and magnetic barriers is proposed. The key is to achieve the comprehensive optimization of the proposed rotor topology to satisfy the different requirements under diverse operating points. Then, a multi-objective automatic parallel optimization method is applied, which simultaneously analyzes multi-condition operation without weight coefficients defined artificially. The 3D Pareto solution set is generated by using nature inspired evolutionary algorithm based on the high-precision metal-modals of optimal prognosis, which reduce the needed computation cost significantly. Moreover, the back electromotive force total harmonic distortion, torque and core loss of the optimal machine are analyzed at corresponding operating points. Finally, the finite-element results are validated by experiments based on a prototype machine.

Effect of Strain on Tunneling Time in Graphene Magnetic Barrier

Effect of Strain on Tunneling Time in Graphene Magnetic Barrier

Research on a permanent magnet assisted synchronous reluctance machine with hybrid excitation

In this paper, the results of simulation tests of a hybrid excited permanent magnet machine operating in various states have been presented. The characteristic feature of this machine is a presence of magnetic barriers inside the rotor. Structurally, this machine combines advantages of the PMa-SynRM machine (Permanent Magnet assisted Synchronous Machine) and a wound synchronous machine. The paper presents the voltage and torque characteristics as a function of the current in the stator and the DC control coil. Additional selected results of experimental studies are also shown.

The Influence of the δ-Doping on the Electron Transport With the Finite Periodic Magnetic Barriers Superlattices

The Influence of the δ-Doping on the Electron Transport With the Finite Periodic Magnetic Barriers Superlattices

Suppression of Cross-Coupling Effect of Hybrid Permanent Magnet Synchronous Motor with Parallel Magnetic Circuit

Hybrid permanent magnet synchronous motor (HPMSM) has attracted increased attention in recent years due to its adjustable air gap flux. However, as a result of the cross-coupling effect of high- and low-coercive permanent magnets, the precise magnetic adjustment of HPMSM has become increasingly difficult. In order to weaken the cross-coupling effect, two methods of adding magnetic barrier and exciting coil are adopted in this paper. First, the equivalent magnetic circuit model is established, and the theoretical rationality of the weakening method is analyzed. Second, the electromagnetic performance of two weakening methods are analyzed based on the finite element analysis. Finally, the rationality of the theoretical analysis is verified, which provides the structure basis for the precise magnetic adjustment of the hybrid permanent magnet motor.

Optimization and Simulation of Auxiliary Magnetic Barrier Permanent Magnet Synchronous Machine for Wind Turbine

The auxiliary magnetic barrier permanent magnet synchronous motor(AMBPMSG) has not only the advantages of high power density and highefficiency of permanent magnet synchronous generator, but also the advan-tages of high temperature non-demagnetization and low cost of the reluctancemotor. It has a broad application prospect in the field of wind power gen-eration. Statement is presented in this paper, on the basis of structure andoperation principle of the motor, the magnetic barrier surrounding the shape,shape of magnetic bridge, magnetic barrier layer and a permanent magnet isoptimized, by means of two-dimensional finite element simulation softwareanalysis of air-gap magnetic field, the counter electromotive force, reduce no-load back electromotive force harmonic content, in order to obtain the optimalelectromagnetic performance, and develop the visual design and simulationplatform software. The research of this paper has a certain reference value forthe popularization and application of AMBPMSG.

The influences of parabolic potential and magnetism on strongly coupled polaron characteristics within asymmetric Gaussian quantum wells

In this research, the effects of magnetism and parabolic potential on strongly coupled polaron characteristics within asymmetric Gaussian quantum wells (AGQWs) were investigated. To do so, the following six parameters were studied, temperature, AGQW barrier height, Gaussian confinement potential (GCP) width, confinement strengths along the directions of [Formula: see text] and [Formula: see text], as well as magnetic field cyclotron frequency. The relationships among frequency oscillation, AGQW parameters and polaron ground state energy in RbCl crystal were studied based on linear combination operator and Lee–Low–Pines unitary transformation. It was concluded that ground state energy absolute value was decreased by increasing GCP width and temperature, and increased with the increase of confinement strength along [Formula: see text] and [Formula: see text] directions, cyclotron frequency of magnetic field and barrier height of AGQW. It was also found that vibrational frequency was increased by enhancing confinement strengths along the directions of [Formula: see text] and [Formula: see text], magnetic field cyclotron frequencies, barrier height AGQW and temperature and decreased with the increase of GCP width.

Unidirectional localization and track-selection of antiferromagnetic skyrmions through tuning magnetocrystalline anisotropy barriers

Reliable detection of antiferromagnetic (AFM) structures remains an open issue in experiments, although these structures such as skyrmions are suggested to play an important role in future spintronic applications. In this work, we theoretically proposed an alternative method to localize the AFM skyrmions along the direction of driving force through tuning magnetic anisotropy barriers by linear lattice defect design. The dependence of the depinning current on the magnitude and width of the defects and temperature is numerically investigated by solving the Landau-Lifshitz-Gilbert equation and also derived based on the Thiele’s theory. The stable pinning of the skyrmion for certain ranges of the injected current is clearly demonstrated, which suggests an effective way in localizing the skyrmion. Based on the calculated results, we propose a method of precise track-selecting of the AFM skyrmions, which are meaningful for future two- and three- dimensional AFM spintronic device design.

Quasistationary states in a quantum dot formed at the edge of a topological insulator by magnetic barriers with finite transparency

A model of quasistationary states is constructed for the one-dimensional edge states propagating along the edge of a two-dimensional topological insulator based on HgTe/CdTe quantum well in the presence of magnetic barriers with finite transparency. The lifetimes of these quasistationary states are found analytically and numerically via different approaches including the solution of the stationary Schrödinger equation with complex energy and the solution of the transmission problem for a double barrier structure. The results can serve as a guide for determining the parameters of magnetic barriers creating the quantum dots where the lifetimes for the broadened discrete levels are long enough for manipulation with their occupation numbers by external fields.

Injection Moulding of Multipolar Polymer-Bonded Magnets into Soft Magnetic Inserts for Rotors in Reluctance Motors

Due to lower magnetic properties of polymer-bonded magnets compared to sintered magnets, a complete redesign of the multipolar soft magnetic flux barriers in rotors with alignment guidelines was carried out to eliminate the frequently used rare-earth magnets, causing a new influence of the outer magnetic field on the cavity by using soft magnetic inserts. Within this new process, the main influencing factors on the magnetic flux density such as filler content, tool temperature, holding pressure and injection velocity were analysed and correlated. The studies were based on the compound of Polyamide 12 and up to a 60 vol.-% of the hard magnetic filler, strontium ferrite. Based on the study, the injection moulding of multipolar-bonded magnets into soft magnetic inserts for rotors and, in turn, into complex geometries can be optimized in terms of the orientation of the filler, the microstructure and the magnetic flux density. The investigations show no significant influence of the process parameters known from the literature such as the mass temperature Tm, which affects the magnetic flux density, as well as the orientation and the microstructure similar to tool temperature Tt, but is less efficient. The main influencing factors identified during the investigations are the tool temperature Tt, the injection velocity vin and the holding pressure ph. As known influencing factors are only based on simple geometries such as ring structures or plates, new factors were determined for complex rotor geometries.

Electronic control of strong magnetic anisotropy in Co-based single-molecule magnets

The observation of large swings in the magnetic anisotropy in ligated ${\mathrm{Co}}_{2}$ dimers has motivated further calculations on single-center Co qubits in quasitetrahedral and quasioctahedral symmetries. In all cases our results indicate that it is the creation of an unquenched orbital moment due to a half-occupied frontier state at the Co center that directly drives large changes in the magnetic anisotropy barriers regardless of whether it is through symmetry breaking, a change in the charge state, or orbital energy reordering. While these observations are computationally demonstrated through our results on both monomers and dimers, the origin of orbital reordering at the Fermi level is not describable in terms of single physical changes. For example, in ligated ${\mathrm{Co}}_{2}$ the appearance of an unquenched orbital moment in one of the Co centers is correlated with a change from antiferromagnetic to ferromagnetic ordering at an energy that is uncharacteristically high for such transitions. Because this raises the spector of electromagnetically switchable quantum devices that operate at higher temperatures relative to that of the first-generation magnetic qubits, we carefully discuss subtle details associated with single-center qubits in realistic atomistic environments.

Comparative Analysis of Parallel Hybrid Magnet Memory Machines with Different PM Arrangements

This paper presents a comparative analysis of two parallel hybrid magnet memory machines (PHMMMs) with different permanent magnet (PM) arrangements. The proposed machines are both geometrically characterized by a parallel U-shaped hybrid PM configuration and several q-axis magnetic barriers. The configurations and operating principles of the investigated machines are introduced firstly. The effect of magnet arrangements on the performance of the proposed machines is then evaluated with a simplified magnetic circuit model. Furthermore, the electromagnetic characteristics of the proposed machines are investigated and compared by the finite-element method (FEM). The experiments on one prototype are carried out to validate the FEM results.

Anomalous transport of electrons in an electric discharge with transverse magnetic field

The experimental data showing the relationship of excitation of microwave oscillations with abnormally transport of electrons across the magnetic field in turbulent plasma are presented. The mechanism of the formation of the discharge current due to scattering of drift electrons in the near-electrode layers of the electric discharges on microwave oscillations has been substantiated. The conditions for the manifestation of the turbulent mechanism of anomalous electron transport through the magnetic barrier at the boundary of the toroidal electric discharge have been studied most fully. The mobility of electrons across a magnetic field is one of the main parameters of electric discharges that use crossed electric and magnetic fields for technological purposes.

Gap-tunable of tunneling time in graphene magnetic barrier

We study the tunneling time of Dirac fermions in graphene magnetic barrier through an electrostatic potential and a mass term. This latter generates an energy gap in the spectrum and therefore affects the proprieties of tunneling of the system. For clarification, we first start by deriving the eigenspinors solutions of Dirac equation and second connect them to the incident, reflected and transmitted beam waves. This connection allows us to obtain the corresponding phases shifts and consequently compute the group delay time in transmission and reflection. Our numerical results show that the group delay time depends strongly on the energy gap in the tunneling process through single barrier. Moreover, we find that the group approaches unity at some critical value of the energy gap and becomes independent to the strengths of involved physical parameters.