Magnetization State Manipulation Research Articles

A Novel Dual Magnetizing Current Controller to Mitigate Speed Fluctuation During Magnetization State Manipulation for Variable Flux Memory Machines

A Novel Dual Magnetizing Current Controller to Mitigate Speed Fluctuation During Magnetization State Manipulation for Variable Flux Memory Machines

Generation of out-of-plane polarized spin current by spin swapping

The generation of spin currents and their application to the manipulation of magnetic states is fundamental to spintronics. Of particular interest are chiral antiferromagnets that exhibit properties typical of ferromagnetic materials even though they have negligible magnetization. Here, we report the generation of a robust spin current with both in-plane and out-of-plane spin polarization in epitaxial thin films of the chiral antiferromagnet Mn3Sn in proximity to permalloy thin layers. By employing temperature-dependent spin-torque ferromagnetic resonance, we find that the chiral antiferromagnetic structure of Mn3Sn is responsible for an in-plane polarized spin current that is generated from the interior of the Mn3Sn layer and whose temperature dependence follows that of this layer’s antiferromagnetic order. On the other hand, the out-of-plane polarized spin current is unrelated to the chiral antiferromagnetic structure and is instead the result of scattering from the Mn3Sn/permalloy interface. We substantiate the later conclusion by performing studies with several other non-magnetic metals all of which are found to exhibit out-of-plane polarized spin currents arising from the spin swapping effect.

Improved Adaptive Sliding-Mode Observer Based Position Sensorless Control for Variable Flux Memory Machines

This paper focuses on the position sensorless control for variable flux memory machine (VFMM), of which the magnetization state (MS) can be flexibly changed by applying a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis current pulse to achieve the so-called MS manipulation. First, the unique challenges in VFMM sensorless control are in depth analyzed and summarized based on experimental results. An improved adaptive sliding mode observer (SMO) and an improved phase-locked loop (PLL) are then proposed. Specifically, a newly developed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -axis voltage pulse injection method is employed to accurately measure the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -axis inductances of VFMM during MS manipulations and update them into SMO to increase its convergence speed. An adaptive law is proposed for tuning sliding mode gains to obtain satisfying estimation performance of SMO under different conditions of speed and MS. In addition, to enhance the position tracking performance against the position estimation error resulted from MS manipulation or speed change, an improved PLL is structured, whose bandwidth can be adaptively adjusted by using fuzzy logic control. Finally, the feasibility and effectiveness of the proposed sensorless control strategy are verified through experimental measurements on a hybrid magnetic circuit VFMM (HMC-VFMM) prototype.

Improved MTPA Control for Variable-Flux Memory Machine With Operating Envelope Prediction-Based MS Manipulation

This article proposes an improved maximum torque per ampere (MTPA) control method for variable-flux memory machine (VFMM) with operating envelop prediction-based magnetization state (MS) manipulation. The proposed method can achieve the MTPA control under the voltage limitation and simplify the MS adjustment process for expanding the operating region. The mathematical model of the studied VFMM is established to calculate the reference current for MTPA control online as well as to predict the operating envelop at each MS. According to the calculated operating envelop, the proposed MS manipulation method can separate the magnetization and demagnetization processes by setting two MS manipulation boundaries correspondingly, which is easily implementable and can avoid frequent MS manipulation processes. Besides, the inductance characteristics of the machine are measured to improve the model accuracy and control performance. Experiments are carried out on a VFMM prototype to validate the feasibility and effectiveness of the proposed method.

Thermal Modeling and Analysis of Hybrid-Magnetic-Circuit Variable Flux Memory Machine

Variable flux memory machine (VFMM) can be regarded as a promising candidate for electric vehicles (EVs) owing to its advantages of excellent flux adjustment capability and overall efficiency improvement over an extended operating range. However, the uncertain internal thermal behavior due to magnetization state (MS) change has an immense influence on electromagnetic performance of permanent magnet, which makes the precise MS estimation of low coercive force PM a challenging issue. To explore the benefits of MS manipulation on temperature rise reduction and provide an effective method to accurately evaluate temperature rise in VFMM, a magnetic-thermal coupling model of the newly developed hybrid-magnetic-circuit VFMM accounting for different MSs is established in this article. The lumped parameter thermal network (LPTN) model and computational fluid dynamics based finite-element (FE) method are employed to analyze the temperature characteristics, respectively. First, the losses of the investigated machine are calculated by adopting both the FE method and analytical equations. Afterward, the equivalent thermal resistances and heat transfer coefficients are determined by employing the LPTN model. Meanwhile, FE modeling is employed to analyze the three-dimensional thermal field distribution. Finally, a prototype machine is fabricated and experimentally measured, which can confirm the validity of the theoretical analyses.

Density Functional Theory Studies on Magnetic Manipulation in NiI2 Layers

Effective manipulation of magnetic states is fundamentally important to modern data storage and electronic devices that underpin the information age. Controlling magnetism via electric fields instead of magnetic fields has long been envisioned as a revolutionary technology to achieve higher energy efficiency and ultimate device miniaturization. The electric field paradigms, however, face major challenges of volatility, high energy cost, and low storage density. In this work, from density functional theory simulations, we developed effective approaches to achieve magnetic control in bilayer NiI2 via electrostatic doping and polarization field of the ferroelectric heterostructure. The interlayer antiferromagnetic (AFM) to ferromagnetic (FM) transition has been observed in bilayer NiI2 when the critical electron doping concentration reaches 0.625% due to the magnetic exchange competition between antiferromagnetic and ferromagnetic couplings. The critical concentration of magnetic transition can be reduced or increased depending on the polarization direction when it is placed on the ferroelectric substrate of Sc2CO2 as a result of polarization-induced interfacial electron transfer. Owing to the antiferromagnetic-to-ferromagnetic (AFM–FM) transition, the reversal of ferroelectric polarization modulates the electronic properties dramatically due to the strong interfacial magnetoelectric effect. The magnetic and electronic manipulation from electrostatic doping and polarization provides feasible approaches for next-generation electronics and spintronics.

Speed Fluctuation Mitigation Control for Variable Flux Memory Machine During Magnetization State Manipulations

This article focuses on the dynamic performance improvement of variable flux memory machine (VFMM), particularly the speed fluctuation mitigation control during magnetization state (MS) manipulations. A model-compensation linear active disturbance rejection (LADR-MC) speed controller is proposed for VFMM speed regulation systems to compensate for the drastic disturbance during MS manipulation and to reduce both the torque and speed fluctuations. An extended state observer (ESO) is employed to provide real-time estimation of disturbances in a lumped term. Additionally, the machine parameters during MS manipulations are identified in advance and utilized in real time to improve the accuracy of disturbance estimation for the ESO. Then, the design procedure of the LADR-MC controller is explained in detail with formulas and diagrams. Finally, the effectiveness and feasibility of the proposed LADR-MC speed controller are verified by experimental results on a hybrid-magnetic-circuit VFMM prototype. The drive system employing the LADR-MC speed controller exhibits better performance in speed fluctuation mitigation compared with those based on the conventional proportional-integral and LADR controllers.

Variable Time Magnetization Current Trajectory Control Method for Variable Flux Memory Machines

Magnetization state (MS) manipulation is crucial to the comprehensive performance improvement of variable flux memory machine (VFMM) drive system. This article proposes a novel MS manipulation control method wherein variable time magnetization current trajectories can be adaptively controlled to reduce the MS manipulation losses. A fuzzy proportional integral (PI) feedforward current controller is newly structured to track the trajectories, improving the current tracking ability. First, dynamic MS manipulation processes are simulated and analyzed deeply, in which the variable machine parameters are calculated by finite element method (FEM) and fitted with polynomial formulas. Based on these, the maximum <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dt</i> of magnetization current pulse trajectory, namely the shortest MS manipulation time, can be adaptively acquired to reduce the MS manipulation losses at different running conditions. Then, a fuzzy PI feedforward current controller is developed by combining the feedforward and fuzzy logic controls, ensuring the real current tracks its reference well at different speed and load conditions, particularly in the MS manipulation process. Finally, the effectiveness and feasibility of the proposed MS manipulation method are verified by experimental results on a hybrid-magnetic-circuit VFMM (HMC-VFMM) prototype.

A Novel Current Control Strategy for Magnetization State Manipulation of Variable Flux Memory Machine Based on Linear Active Disturbance Rejection

In this article, a novel current control strategy is proposed to manipulate the magnetization state of the variable flux memory machine (VFMM) through a newly developed linear active-disturbance-rejection-based feedforward current controller. A linear extended state observer is designed to estimate the sum of the permanent magnet (PM) induced voltage and the disturbance voltage caused by the susceptible machine parameters to compensate for the linear state error feedback output. The voltage across the winding resistance and the cross-coupling voltage are calculated by the voltage equations and fed forward to the output of the current controller. Meanwhile, the magnetizing current pulse amplitude can be determined by the target PM flux linkage obtained by looking up the table according to the mechanical speed. Since the q -axis disturbance voltage can commonly be ignored during the steady operation, the q -axis observed voltage after low-pass filtering can be directly utilized to estimate the PM flux linkage, which is compared with the target PM flux linkage to determine whether the current manipulation is needed to achieve online remagnetization or demagnetization. Experimental measurements on a hybrid-magnetic-circuit VFMM verify the effectiveness and superiorities of the proposed current control strategy.

Closed-Loop Magnetization State Control for a Variable-Flux Memory Machine

Variable flux memory machines (VFMM) use magnetization and demagnetization manipulations to adjust machine voltage, achieving wide-speed high-efficiency operation. The machine magnetization state manipulation is a critical concern in the VFMM control. Thus, this article proposes an on-line magnetization state estimation and closed-loop control using the magnetization manipulation signals. The magnetization state manipulation requires voltage injection to create the manipulation current. The current shows non-linear response at different magnetization state because the current changes the magnets state and the machine saturation level. The flux change rate, which is calculated by the injected voltage and the current response, is affected by the non-linearity and utilized in the proposed method for the magnetization state estimation. The proposed magnetization state estimation achieves self-sensing characteristic because the signals in the estimation already exist in the magnetization state manipulation. Based on the estimated and the target magnetization state, the closed-loop magnetization state control is achieved by the voltage injection regulation.

Second-Order Sliding Mode-Based Direct Torque Control of Variable-Flux Memory Machine

The variable-flux memory machine (VFMM) exhibits high efficiency over a wide speed range because its airgap magnetic flux can easily be regulated by varying the magnetization state (MS) of the employed low coercivity force permanent magnets. This paper proposes a second-order sliding mode (SM)-based direct torque control (DTC) strategy for the VFMM, which features a relatively low computational complexity and less dependence on machine parameters. The operating principle and mathematical model of the VFMM are first described and established. On this basis, a novel control scheme combining the DTC strategy with MS manipulation is proposed, in which the machine is controlled by utilizing the DTC strategy incorporating the $i_{\mathrm {d}} = 0$ condition, while the MS manipulation is implemented by energizing reference stator flux linkage pulses. A super-twisting second-order SM controller is subsequently developed to achieve strong robustness. The developed control structure avoids a complicated decoupling algorithm and is simpler than that of the conventional field-oriented control (FOC) method. Finally, the effectiveness of the proposed control scheme is validated by simulation and experimental results.

Analysis, Modeling, and Current Trajectory Control of Magnetization State Manipulation in Variable-Flux Permanent Magnet Machines

Magnetization and demagnetization current control is a critical part of the variable-flux permanent magnet machine control, but the variable-flux properties and saturation effects deteriorate conventional current controller performances. Thus, this paper proposes an improved feed-forward current controller that compensates voltage variations during the magnetization and demagnetization manipulations, obtaining better control performances. The compensation voltages are analyzed by finite-element method, and a modified mathematical model is developed to present the relation among the voltages, the flux linkages, and the manipulation currents. This model considers induced voltage and variable electromotive force, which are caused by the change of the permanent magnet flux linkage during the manipulations. Based on the model, the induced voltage, the cross-coupling rotating voltage, and the resistance voltage are compensated in the proposed feed-forward controller. This controller is verified by experiments, showing fast response and accurate trajectory tracking advantages.

Magnetization State Manipulation Method to Reduce Back Electoromotive Force in High Speed Region of Variable Flux PMSMs and a Study of Vehicle Torque Vibration

Magnetization State Manipulation Method to Reduce Back Electoromotive Force in High Speed Region of Variable Flux PMSMs and a Study of Vehicle Torque Vibration

A Review on Variable Flux Machine Technology: Topologies, Control Strategies and Magnetic Materials

Modern applications demand challenging operation requirements from electrical machines. Variable-flux machine (VFM) concepts are found to offer new opportunities for improved machine design. This paper reviews the VFM technology. Three topologies, mainly the parallel hybrid VFMs, series hybrid VFMs, and variable-flux flux intensifying type VFMs are discussed in detail. The variable-flux flux Intensifying machines are found to be the state-of-the-art VFM technology available to-date. The paper also reviews the magnetization process in the VFMs and relates this with the B-H curve of the magnetic material. The conventional PM machine mathematical model is adapted to represent the operation of the VFMs. The different operational limitations of the VFMs are explained and the different modes of operation of the VFMs have been reviewed and compared. The magnetization state manipulation techniques are reviewed. The AC magnetization is found to be the more preferable approach to reduce weight and manufacturing complexity of the VFMs. The trapezoidal current pulse based approach is popular in AC magnetization state manipulation, however, new advanced forms of current vector trajectory control techniques offer comparatively better magnetic state manipulation and higher speed capability for remagnetization of the magnets in the VFMs. The paper also reviews the different magnetization state estimation techniques that are useful during control systems development for the VFMs. The magnetic material for the VFM design is reviewed and potential alternative magnetic material that can satisfy the requirements of the VFMs have been identified. Finally, the current status, challenges, and the potential of VFMs technology are discussed in the conclusion of the paper.

Manipulation of dipolar magnetism in low-dimensional iron oxide nanoparticle assemblies.

The manipulation of magnetic states in nanoparticle supercrystals promises new pathways to design nanocrystalline magnetic materials and devices. Trench-patterned silicon substrates were used as templates to guide the self-assembly of iron oxide nanoparticles. Grazing incidence small angle X-ray scattering shows that the nanoparticles form a long-range ordered structure along the trench direction while in the direction perpendicular to the trenches, no coherent structure is observable. Electron holography provides evidence of an ordered magnetic state of nanoparticle moments in the remanent state after the application of a saturation magnetic field parallel to the trenches. However, a disordered magnetic state was observed in a perpendicular geometry. Hysteresis loops indicate that the nanoparticle moments form a superferromagnetic state for the geometry parallel to the trenches. Memory effect investigations reveal that the disordered magnetic state corresponds to a collective superspin glass state in the perpendicular geometry, while the superferromagnetic state in the parallel geometry suppresses the superspin glass state.

Enabling Driving Cycle Loss Reduction in Variable Flux PMSMs Via Closed-Loop Magnetization State Control

Variable flux permanent magnet synchronous machines (VF-PMSMs) have recently been proposed to reduce driving cycle losses in electric vehicle traction motors via magnetization state (MS) manipulation. This paper presents a closed-loop MS control method to enable reliable loss minimization control of VF-PMSMs. The MS is estimated at every sample instant and is used as a feedback for closed-loop control. Under most circumstances, the proposed method maintains precise torque control even during the MS manipulation transient by using a deadbeat-direct torque and flux control (DB-DTFC) framework. The state-of-the-art high-speed flux trajectory generation method for MS manipulation is integrated in the new closed-loop method to allow MS manipulation up to the maximum speed within the inverter voltage limit. The effectiveness of the proposed methods, in terms of driving cycle loss reduction capability and its thermal impact, is evaluated experimentally by emulating the road load using the dynamometer load motor.

Variable Flux Permanent Magnet Synchronous Machine (VF-PMSM) Design Methodologies to Meet Electric Vehicle Traction Requirements with Reduced Losses

Variable flux permanent magnet synchronous machines (VF-PMSMs) in which the magnetization state of low coercive force permanent magnets can be actively controlled to reduce losses in applications that require wide-speed operation have been proposed recently. While prior focus has been on achieving magnetization state manipulation without oversizing the inverter and obtaining higher torque capability, this paper extends the design objectives to include the power requirements of an electric vehicle traction motor over its entire speed range. Finite-element methods are used to study the effect of combinations of low coercive-force and high coercive-force permanent magnets arranged in either series or parallel on the performance of VF-PMSMs. While both configurations help improve the torque density, only the series configuration can help improve the high speed power capability. Experimental results showing the variable magnetization state property, torque-speed capability, and loss reduction capability of a series magnet configuration VF-PMSM test machine are presented.

Piezoelectric control of magnetoelectric coupling driven non-volatile memory switching and self cooling effects in FE/FSMA multiferroic heterostructures

The manipulation of magnetic states and materials' spin degree-of-freedom via a control of an electric (E-) field has been recently pursued to develop magnetoelectric (ME) coupling-driven electronic data storage devices with high read/write endurance, fast dynamic response, and low energy dissipation. One major hurdle for this approach is to develop reliable materials which should be compatible with prevailing silicon (Si)-based complementary metal–oxide–semiconductor (CMOS) technology, simultaneously allowing small voltage for the tuning of magnetization switching. In this regard, multiferroic heterostructures where ferromagnetic (FM) and ferroelectric (FE) layers are alternatively grown on conventional Si substrates are promising as the piezoelectric control of magnetization switching is anticipated to be possible by an E-field. In this work, we study the ferromagnetic shape memory alloys based PbZr0.52Ti0.48O3/Ni50Mn35In15 (PZT/Ni-Mn-In) multiferroic heterostructures, and investigate their potential for CMOS compatible non-volatile magnetic data storage applications. We demonstrate the voltage-impulse controlled nonvolatile, reversible, and bistable magnetization switching at room temperature in Si-integrated PZT/Ni-Mn-In thin film multiferroic heterostructures. We also thoroughly unveil the various intriguing features in these materials, such as E-field tuned ME coupling and magnetocaloric effect, shape memory induced ferroelectric modulation, improved fatigue endurance as well as Refrigeration Capacity (RC). This comprehensive study suggests that these novel materials have a great potential for the development of unconventional nanoscale memory and refrigeration devices with self-cooling effect and enhanced refrigeration efficiency, thus providing a new venue for their applications.

Manipulation of Magnetic State in Armchair Black Phosphorene Nanoribbon by Charge Doping.

Using first-principles studies, we investigated the width-dependent magnetic properties of armchair black phosphorene nanoribbons (APNRs) by controlling the electron charge doping. In the unrelaxed APNRs the antiferromagnetic coupling between two phosphorus atoms in the same edge was found. However, the edge magnetic moment vanished after structure relaxation, and all of the APNRs showed a semiconducting feature. Interestingly, the charge doping substantially altered the band structures of the APNRs because the metallic states reappeared in the charge-doped APNRs. Besides this, the magnetic moment was found in the charge-doped systems. We found that the Stoner condition could nicely explain the magnetic moment at the edge atoms. Moreover, we propose that the edge-to-edge magnetic coupling can be manipulated by charge doping because the transition from the antiferromagnetic to ferromagnetic state was achieved. Our findings may bring interesting issues for spintronics applications.

Manipulation of magnetic state in phosphorene layer by non-magnetic impurity doping

Using the full-potential linearized augmented plane wave method, we have explored the structural, electronic band structure, binding energy, and magnetic properties of a non-magnetic impurity (Al, Si, S, and Cl) doped phosphorene layer. The binding energy showed a tendency to decrease with increasing atomic number. Nonetheless, we still found large binding energies of 5.1 eV ∼ 8.3 eV. We observed that the electronic band structure and magnetic property were strongly dependent on the specific impurity atom. For instance, we propose that the Al doped system will show a semiconducting transport property. In all other systems, we found metallic band structures. We predict that the Al and Si impurity act as donor elements whereas the S and Cl impurities behave as acceptor elements. Interestingly, the magnetic state appeared in Si, S, and Cl doped systems while the Al impurity induced no spin polarized state. In the Si doped system, the major contribution to a magnetic moment originated from Si impurity itself, while the presence of dangling bonds at a neighboring P atom near the impurity site plays a crucial role for magnetism in S and Cl doped systems. On the other hand, interestingly, we observed a half metallic feature in the S doped layer. Overall, we have found that the magnetic state can be manipulated by even non-magnetic impurity doping in a phosphorene layer.