Magnetic Resistance Research Articles

Temperature and thickness dependent magnetization reversal in 2D layered ferromagnetic material Fe3GeTe2

Advance in the field of two-dimensional (2D) Van der Waals layered magnetic materials have made the atomic-thickness spintronic devices possible in the near future. The application of the 2D layered magnetic materials inevitably involves the magnetization reversal. Here we study the magnetization reversal of the 2D layered material Fe3GeTe2 by means of magnetic and anomalous Hall resistance measurements. We find the reversal process of Fe3GeTe2 flake is temperature and thickness dependent. For thin flakes and at low temperatures, the hysteresis loops have perfect rectangular shapes with large coercivity, indicating the single domain characteristic during the reversal process. With increasing temperature, a cross-over from single domain to multi-domain structure occurs. For bulk and very thick flakes Fe3GeTe2, the nearly zero magnetic remanence and small coercivity demonstrates that the reversal process is accomplished through the formation of multi-domain structure and its gradual evolution with the magnetic field. The change of magnetization reversal with temperature and flake thickness is explained based on the competition between the long-range magnetic dipolar interaction and the perpendicular magnetic anisotropy. The results obtained in this work provide important reference for designing Fe3GeTe2-based spintronic devices.

Effect of sintering temperature on structure and electrical transport properties of La0.7Ca0.26Na0.04MnO3 ceramics

LCNMO (La0.7Ca0.26Na0.04MnO3) ceramics are prepared via the sol-gel method and sintered at different temperatures, ranging from 1000 to 1300 °C. The influences of sintering temperature on structure and electrical properties are systematically investigated. X-ray diffraction analysis reveals that uniform phase of perovskite structure is formed after sintering. Furthermore, scanning electron microscope (SEM) images demonstrate the presence of on the surface, a highly dense grain boundary and an average grain size of ~2.5 μm. The resistivity-temperature (ρ-T) measurement shows that the resistivity decreases with increased sinter temperature. Moreover, the metal-insulation transition temperature (Tp) and peak resistivity (ρmax) gradually decreased with increasing sintering temperature. The influence of various scattering mechanisms on resistivity at low temperatures is studied, revealing that the residual resistivity (ρ0) dictates the electrical transport performance of the LCNMO ceramics. Also, the different models employed to analyze the ρ-T curves in the temperature range of 100–300 K, confirming the occurrence of phase-separation mechanism in the entire temperature range. The resistance temperature coefficient (TCR) of 10.6%·K−1 and maximum magnetic resistance (MRmax) of 57.12% are achieved after sintering at 1200 °C. These results indicate that LCNMO are promising candidates for infrared detector and magnetic sensor.

Research on the Non-Magnetic Conductor of a PMSM Based on the Principle of Variable Exciting Magnetic Reluctance

A permanent magnet synchronous motor (PMSM) based on the principle of variable exciting magnetic reluctance (VMRPMSM) is presented. The motor is equipped with symmetrical non-magnetic conductors on both sides of the tangential magnetized permanent magnets (PMs). By placing the non-magnetic conductor (NMC), the magnetic reluctance in the exciting circuit is adjusted, and the flux weakening (FW) of the motor is realized. Hence, the NMC is studied comprehensively. On the basis of introducing the motor structure, the FW principle of this PMSM is described. The shape of the NMC is determined by analyzing and calculating the electromagnetic force (EF) acting on the PMs. We calculate the magnetic reluctance of the NMC and research on the effects of the NMC on electromagnetic force, d-axis and q-axis inductance and FW performance. The critical speeds from the test of the no-load back electromotive force (EMF) verify the correctness of the NMC design. The analysis is corresponding to the test result which lays the foundation of design for this kind of new PMSM.

Improved Method for Distributed Parameter Model of Solenoid Valve Based on Kriging Basis Function Predictive Identification Program

In this paper, a method for the improvement of the calculation accuracy of the distributed parameter model (DPM) of electromagnetic devices is proposed based on the kriging basis function predictive identification program (PIP). Kriging is mainly an optimal interpolation method which uses spatial self-covariance, and takes a polynomial as the basis function. The accuracy of the kriging-based surrogate model can be improved by adjusting the related functions and hyperparameters. Based on the DPM of a solenoid valve, there exist certain errors in the estimation. They can be summarized as follows: Firstly, the estimation error of magnetic flux leakage (MFL) permeance is caused directly by the deviation of the magnetic flux tube due to the segmented magnetic field line. Secondly, the estimation error of soft magnetic resistance because of the nonlinearity of the permeability of soft magnetic material leads to the change of soft magnetic resistance alongside the magnetic flux. In this paper, an improved kriging error correction method is applied to modify the leak permeance and soft magnetic resistance calculation. The kriging basis function is adjusted to adapt to the data curve of the MFL permeance error data. The calculated MFL permeance data are compared with the error variation data to select the appropriate basis function. To improve the computational efficiency, the PIP is proposed to select the appropriate basis function. The modified MFL permeance data and soft magnetic resistance are substituted into the DPM for improving the computational accuracy and efficiency of the solenoid valve.

Numerical simulation and analysis of running magnetic resistance in the evacuated tube SS-HTS magnetic levitation system

ABSTRACT The evacuated tube side-suspended high-temperature superconducting (SS-HTS) magnetic levitation prototype vehicle can run at high speed on a uniform permanent magnet guideway due to the characteristics of magnetic flux pinning. However, permanent magnet guideway with magnetic fluctuations will cause resistance in the running direction of the high-temperature superconducting maglev prototype vehicle, which will inevitably affect its running stability. In order to study the influence of magnetic field gradient and running speed on the magnetic resistance of the high-temperature superconductor in the direction of running, a three-dimensional model is established using the finite element software COMSOL Multiphysics to calculate the magnetic resistance of the high-temperature superconductor when it passes through a permanent magnet guideway. The results show the influence of the magnetic field gradient of the permanent magnet guideway and the running speed of the prototype car on the magnetic resistance to various degrees.

Extended State Observer-Based IMC-PID Tracking Control of PMLSM Servo Systems

Servo systems driven by a permanent magnet linear synchronous motor (PMLSM) are often affected by uncertain disturbances, such as magnetic resistance, friction, and external disturbances, which increase tracking errors and reduce motion accuracy. Traditional control methods may have difficulty to achieve satisfactory control performance in terms of tracking accuracy and disturbance rejection. In this paper, we propose an internal model control PID method based on a model linear extended state observer, which is termed as IMC-PID-MLESO method. With this method, the nominal model parameters of the PMLSM servo system are obtained via system identification. The model linear extended state observer (MLESO), with known parameter information, is designed to improve the estimation accuracy for the system states and total unknown uncertainties. As the uncertainties are compensated in the feedback control law, the PMLSM servo system model is transformed into a known nominal model. Based on the nominal model, the IMC-PID feedback controller is designed to ensure satisfactory performance on disturbance rejection and tracking error reduction. Simulation and experimental results show that the IMC-PID-MLESO method can effectively improve the position tracking accuracy of the PMLSM servo system and rapidly suppress the system disturbance.

The Influence of Carbonitration on the Magnetic Properties of Electrical Steel

The influence of carbonitration on the magnetic properties, hardness, and wear resistance of unalloyed electrical steel grade 10 895 was investigated. It was found that carbonitration increased the surface hardness from HV = 140 to 580. This is not as important as when applying borides and nickel borides (HV 2015) but is still very significant (4.1-fold), with a 90% increase in the wear resistance being achieved with friction on the Ferodo disk. Due to the improvement of the magnetic properties of steel, the torque of the magnetic clutch MWU increased by 40%.

Magnetic Field Energy Harvesting From Current-Carrying Structures: Electromagnetic-Circuit Coupled Model, Validation and Application

Magnetic field energy harvesters (MFEHs) from current-carrying structures/conductors are usually modelled as decoupled electromagnetic and electrical systems. The current-carrying structures may affect the performance of MFEH through the generation of the eddy current and the alteration of the magnetic reluctance. Moreover, the load circuit affects the current generated in the coil and therefore the flux density and eddy current generated. The effects of the current-carrying structure and the load circuit cannot be fully described by the decoupled models. This work develops a finite element model (FEM) that fully couples the electromagnetic and electrical systems by simulating both the magnetic field and eddy current distribution of an MFEH connected to an electrical circuit. The FEM first simulates the coil inductance and resistance of a magnetic field energy harvester (MFEH) placed close to a current-carrying structure exemplified by a rail track. The FEM then simulates the outputs of the MFEH connected to an electrical circuit consisting of a compensating capacitor and optimal load resistor determined by the first step. An MFEH was fabricated and tested under a section of current-carrying rail track. Both experiment and simulation show an increase of both coil resistance and inductance when the MFEH is placed close to the rail track. The good agreement between experimental and simulation results validates that the FEM can predict the full-matrix performances of the MFEH, including the coil parameters, power output and magnetic flux density under the influence of the current-carrying structure and the load circuit. Simulation results reveal that in addition to the permeability of the magnetic core, the electrical conductivity and magnetic permeability of the current-carrying structure considerably affect the performance of the MFEH, which cannot be predicted by decoupled models.

Harmonic Suppression and Torque Ripple Reduction of a High-Speed Permanent Magnet Spindle Motor

In this paper, the method of harmonic suppression and torque ripple reduction is studied for the structure characteristics and design requirements of a high-speed permanent magnet spindle motor. According to the magnetic circuit analysis and calculation theory of the permanent magnet synchronous motor (PMSM), magnetic reluctance slots are arranged at the two ends of the rotor yoke to change the external magnetic field distribution of the permanent magnet in order to optimize the air gap magnetic density waveform. To obtain air gap flux density waveforms that are close to a sinusoidal distribution and not destroy the permanent magnet under the pre-pressure, several reluctance slots with different widths and depths arranged at two ends of the rotor yoke are used to achieve the sinusoidal distribution. Based on the selection of the pole-slot proportion, skewed-slot and a decrease in the end effect, the effects of the harmonic suppression of the harmonic electromotive force (EMF) and the reduction in the torque ripple are discussed. It is concluded that the additional loss and torque ripple of the high-speed permanent magnet spindle motor can be reduced through a reasonable design.

Calculation of the current converters magnetic circuits taking into account the dependence nonlinearity of the specific magnetic resistance relative the magnetic induction

The magnetic circuits of a current converter, the work principle of which is based on the nonlinearity of the magnetization curve, are considered. In order to improve the analytical calculation accuracy of magnetic circuits, it is necessary to establish a relationship between the specific magnetic resistance and magnetic induction. Methods for solving differential equations for magnetic circuits of a converter with longitudinally distributed parameters and an expression for the dependence of the specific magnetic resistance relative the magnetic induction are presented. Keywords electromagnetic current converter; magnetic circuit; nonlinearity of the magnetization curve; magnetic flux; magnetomotive force; quasi-linearization method; machine method of calculation

Application of coercimetry to assess the functional properties of materials

The purpose of this work is a comparative study of the possibilities of various types of coercimeters to assess the functional properties of ferromagnetic materials. Conducted research have shown that the limitation of the maximum measured value of the coercive force using an attached transducer with a U-shaped electromagnet is due to the lower value of the magnetic resistance of the tested workpiece. The upper limit of measurements of the coercive force using a two-pole transducer is determined by the magnitude of the tangential component of the magnetic field only by the possibility of magnetizing the tested object.

A miniaturized giant magnetic resistance system for quantitative detection of methamphetamine.

Point-of-care testing (POCT) systems have been greatly developed in recent years. Among them, lateral flow immunoassay (LFIA) based on magnetic nanoparticles (MNPs) is widely used in various fields due to the advantages of small background noise and good biocompatibility. This paper designed an ultra-sensitive giant magnetic resistance (GMR) system for the quantitative detection of methamphetamine (MET). The system uses GMRs to detect the distribution of the magnetic field intensity of MNPs captured by the test (T) and control (C) lines on LFIA. A special external interference cancellation (EIC) method and a weak-signal waveform reconstruction method were used to improve the accuracy of the detection. Finally, the T/C ratio was calculated to realize the quantitative detection of MET. The result showed good linear performance with a detection limit of 0.1 ng mL-1. The system can also be used in other fields such as disease detection, food analysis, and environmental testing.

Modeling in Software Environments for the Study of the Physical Properties of Ferromagnets

The work is devoted to the study of the properties of ferromagnets in different software environment. The use of magnetic properties of substances is based on whole sections of technology, such as magnetic recording of sound and images, magnetic flaw detection, magnetic exploration of minerals. There are various types of magnetic materials, among which ferromagnets have the most practical application. They are used as cores in transformers, generators, electric motors and other devices. The study of magnetic properties can be carried out both by hardware methods of direct measurements and by simulation. Traditionally, modeling of properties of both bulk and film structures is performed using statistical Monte Carlo numerical methods. At the moment, it is possible to make correlations between the crystalline structure of a magnetic material, the intensity of a ferromagnet, and the change in magnetic properties, such as the coefficient of magnetic resistance. The presented work demonstrates a method of studying the properties of ferromagnets using simulation in the software environments Proteus Professional Demonstration and MULTISIMTM for EDUCATION. The features of these software environments are analyzed. The simulation is performed by constructing in the software environments a circuit with a transformer and an oscilloscope, which determines the characteristics of hysteresis loops. To study the magnetic properties, we proposed a circuit, which includes resistors R0, R1, R1, capacitor C, ammeter, transformer T, power supply and oscilloscope outputs. The magnetic properties of the ferromagnetic material were investigated by analyzing hysteresis loops in a 500 Hz magnetized field using an electron beam oscilloscope. The studied ferromagnet in the form of a toroid has a magnetizing (primary) and measuring (secondary) windings, the number of turns of which influence on the final results of the shape of hysteresis loop. It is shown how the transformer parameters and circuit components affect the appearance of the hysteresis loop. The characteristics of hysteresis loops and their relationship with the properties of the ferromagnet are analyzed. The paper presents the instruction for hysteresis loops observation on the oscilloscope. Methods of measurements, equestions, and calculations of magnetic characteristics are presented: coercive force, residual induction, magnetic permeability, magnetization. The features of modeling in each software environment are analyzed.

УДОСКОНАЛЕННЯ КЕРУВАННЯ ЛІНІЙНИМ ЕЛЕКТРОМАГНІТНИМ ПРИСТРОЕМ З ПОКРОКОВИМ РУХОМ ЯКОРЯ

The improved operation of the linear electromagnetic device (LED) is proposed, without the use of additional sensors for control motion of mobile link LED and automation of technological process. Research focused on determination of the relationship of changes in active inductive parameters of the LED with its design parameters when moving the mobile link of LED and construction an improving the operation, that controls these changes for the increasing the efficiency of their functioning. For this research a theories of electrical circuits and electronic circuits were implemented, which takes into account the change in electrical parameters when moving the mobile link of the linear electromagnetic device. It is proved the dependence of the magnetic resistance in certain sections of the magnetic circuit from the position the mobile link and the design parameters of the LED, the intervals of the magnetic resistance change when the mobile link is moved by the size of the step. The accordance is found between the change in active - inductive parameters when the position of the moving link

Infectious-immune pericarditis: clinical assessment, diagnostics, and differentiated baseline therapy with hydroxychloroquine

Aim. To study the clinical spectrum of infectious-immune pericarditis, the potential for their invasive and non-invasive diagnosis, as well as long-term treatment with hydroxychloroquine (in comparison with other baseline therapy options).Material and methods. The study included 44 patients with infectious-immune pericarditis (28 women and 16 men aged 49,4±13,3 years). Patients with transudate and specific types of pericarditis were excluded. Levels of C-reactive protein and anticardiac antibodies were determined Multislice computed tomography of the lung (n=23) and heart (n=16), cardiac magnetic resistance tomography (n=9), scintigraphy (n=14), and if necessary — immunoelectrophoresis, DNA testing, Diaskin-test. Pericardio- and thoracentesis were performed in 3/3 patients, thoracoscopic pericardial biopsy — 1, endomyocardial biopsy — 7. The follow-up period was 14,5 [3; 39,5] months.Results. Isolated pericarditis was diagnosed in 10 patients (22,7%), myopericarditis — in 34 (77,3%). In 38 patients, pericarditis was exudative: in 24 (63,2%) with a small effusion (<10 mm), in 10 (26,3%) — with a moderate (11-20 mm), in 4 (10,5%) — with a large (>20 mm). Fibrin was detected in 18,2% of patients. Pericardial effusion was assessed as acute in 4, subacute — in 8, chronic — in 26 patients. The connection between the disease onset and infection was found in 56,8% of patents, and inflammatory blood changes — in 59,1%. In 80%, the punctate was lymphocytic; endomyocardial biopsy confirmed active/ borderline (5/2) lymphocytic myocarditis (virus-positive — in 3 patients). Anticardiac antibody titers were increased in 88,2%. Baseline therapy included NSAIDs (34,1%), colchicine (27,3%), hydroxychloroquine (43,2%), methylprednisolone (56,8%, 16 [16; 21] mg/day), azathioprine (20,5%). The treatment scheme was selected individually. In most cases, combined therapy was carried out. The results of treatment were assessed in 36 patients: an excellent effect was noted in 16 (44,4%) patients, stable effect — in 13 (36,1%), no stable effect — in 7 (19,4%). There were no cases of constrictive pericarditis, acute relapses, cardiac tamponade. Mortality of 6,8% was associated with myocardial injury.Conclusion. Criteria for the diagnosis of infectious-immune pericarditis were proposed. An increase in the titer of anticardiac antibodies was noted in all types of the disease. Prescription of corticosteroids is justified in many cases, including in combination with colchicine, cytostatics, hydroxychloroquine. Hydroxychloroquine monotherapy is effective for subacute/chronic pericarditis with moderate effusion.

Static and Dynamic Modeling of the Electromagnets of the Maglev Vehicle Transrapid

This work provides a new approach for modeling the electromagnets of the magnetic levitation (Maglev) vehicle Transrapid intending to effectively and efficiently represent the statics and the dynamics in a frequency range relevant for Maglev control design and for the use in mechatronic simulation models. It includes the effects of magnetic reluctances, fringing and leakage flux, magnetic saturation, and eddy currents. The modeling follows a systematic approach by setting up the equivalent magnetic and electric circuits, and coupling the equations using Ampère's circuital law and Faraday's law of induction resulting in a system of differential algebraic equations. It allows to study effects occurring in the magnet design process or different operating points, resulting, e.g., from aerodynamic uplift, for which an extended validity range is needed. Since the computational effort of such models is significant, additionally, a numerical procedure for model reduction is presented yielding a simplified version, which possesses a nearly identical input-output behavior and is usable for control design or in large vehicle models. The proposed approach can be applied to any levitation or guidance magnet of the vehicle and is shown exemplarily for a Transrapid's levitation magnet. The model is validated for the parameters of the latest Transrapid vehicle, called TR09, showing good correspondence with the measured static force-current-gap characteristics and the inductance.

Investigation of Torque Improvement Mechanism in Emerging Switched Flux PM Machines

This article aims to investigate and reveal the torque enhancement mechanism in several emerging switched flux permanent magnet (SFPM) machines using a unified torque equation with an improved winding factor function. Based on a hybrid finite-element (FE)–analytical method, the torque contributions of the major air-gap field harmonics in the conventional, C-core and E-core, and consequent-pole (CP) SFPM machines are identified and quantified by taking a conventional 12-stator-slot/13-rotor-tooth (12s13r) SFPM machine as a benchmark, which shows that the dominant torque proportions are contributed by the low-order field harmonics due to the amplification effect of the gear ratio. Besides, a low-order field harmonic impeding effect is observed in the conventional and C-core SFPM structures, resulting in a compromised torque capability. Whereas since the auxiliary teeth and stator iron bridge designs provide relatively lower magnetic reluctances for low-order harmonics, the E-core and CP structures can produce improved low-order harmonics and higher torques than the conventional one. Finally, some experiments on a CP-SFPM machine are conducted to validate the theoretical and FE analyses.

Effect of a high magnetic field on the macro- and microstructures of Zn-Mg alloy during semi-solid isothermal annealing process

Zn-Mg alloy was isothermally annealed in the semi-solid range under a high magnetic field (HMF). Results showed that, regardless of the HMF, the specimens exhibit inhomogeneous structures, i.e., primary Zn-rich dendrites and granular (nearly spherical or platelike in three dimensions) particles are distributed in the upper and lower parts, respectively. Applying the HMF and decreasing the annealing temperature significantly contribute to the structural homogeneity, which are ascribed to the induced magnetic viscosity resistance force and the higher viscosity of the interdendritic liquid, respectively. Moreover, the HMF aligns the primary dendrites and platelike particles with their longer axes parallel to the HMF direction B. In addition, the HMF preferentially orients all the granular particles with their c-axis perpendicular to B, regardless of their sizes and shapes. The regular alignment and preferential orientation are related to the magnetocrystalline anisotropy of the primary Zn-rich crystals.

MHD Simulation of Physical Processes in Spherical Plasma-Focus Chambers with Allowance for Neutron Generation

The results of the development of a two-dimensional MHD code for carrying out computational studies of the dynamics of plasma current sheath in spherical chambers with a plasma focus are presented. Equations of magnetohydrodynamics with allowance for magnetic field diffusion, thermal conductivity and plasma radiation are used in this work. An implicit scheme is used in the calculation of the magnetic field, which makes it possible to describe the motion of plasma in a low-density region behind the plasma sheath. The formulas that take into account the possible appearance of anomalous resistance in the plasma are used to calculate the plasma conductivity. The neutron yield is calculated with allowance for thermonuclear and beam–target neutron generation mechanisms. The effect of the minimum residual gas density behind the plasma sheath on the cumulation of the plasma sheath is studied. The effects of magnetic field diffusion, thermal conductivity and anomalous plasma resistance on the plasma sheath dynamics are considered. The calculations are performed for two spherical plasma-focus chambers operating with currents up to 1 and 2 MA and neutron yields to 1012 and 1.5 × 1013 DT neutrons, respectively. The comparison of the calculated dependences with experimental data on the current, voltage and neutron yield made it possible to refine the parameters used in the calculations and achieve a satisfactory agreement between the simulation and experiment.

Design and analysis of permanent magnet biased radial magnetic bearing with external rotor for vacuum tube

A permanent magnet biased radial magnetic bearing with external rotor for vacuum tube was introduced, and the configuration and operating principle were analyzed. The parameter design method based on the total magnetic flux was established to deduce the calculation formulas of the parameters of the permanent magnet radial magnetic bearing. The magnetic flux leakage coefficient and the magnetic resistance coefficient were considered, and the calculations were constrained to the degree of magnetic flux density unsaturation of the internal magnetic field of the soft magnetic material. Finite element software was used to execute simulation analysis and modeling of the permanent magnet biased radial magnetic bearing. The results show that the design method is reasonable and efficient, and the design magnetic bearing is compact and easy to control, which is more suitable for the liner motion with low power consumption.