France



Spin current is a key concept in spintronics. In nonmagnetic metals, the spin-orbit coupling has been utilized for the spin current generation. Recently, an alternative scheme using emergent magnetic fields in moving media is demonstrated [1-5]. In this talk, we will present our recent results on spin transport in nonmagnetic metals driven by a variety of emergent magnetic fields originating from:&lt;br/&gt;1. Liquid metal flow [2,3].&lt;br/&gt;2. Elastic motion [2,4].&lt;br/&gt;3. Rigid rotation [1,5].&lt;br/&gt;4. Non-uniform conductivity of gradient material [6].&lt;br/&gt;5. Surface plasmon polaritons [7,8].&lt;br/&gt;&lt;br/&gt;Firstly, we consider the spin-current generation in moving media. In a moving media, such as elastic materials with the Rayleigh type surface acoustic wave is excited or a pipe flow of liquid metal,  the vorticity field couples to conduction electron spin. As a result, the mechanical angular momentum of the moving media is converted into spin angular momentum.  In particular, a spin current is generated along the vorticity gradient [2,3,4].  It should be noted that the mechanism using the spin-vorticity coupling is free from the strength of the spin-orbit coupling, and thus, weak spin-orbit coupling materials such as Cu can be utilized for the spin-current source [4].&lt;br/&gt;In a rigid rotating metal,  the conventional spin-orbit coupling is augmented due to the emergent magnetic field originating from mechanical rotation [1]. The mechanically induced spin-orbit coupling leads to the spin Hall effect [1]. We introduce a theory of the mechanical analog of the spin Hall effect and an experimental demonstration using magneto-optical detection of spin accumulation under the influence &lt;br/&gt;of mechanical rotation [5]. &lt;br/&gt;&lt;br/&gt;Next, we will discuss our recent experimentally demonstration of the nonreciprocal generation of spin current in a surface-oxidized copper film [6]. This nonreciprocity relies on the transfer of angular momentum from the velocity field of conduction electrons&#39; collective motion.  &lt;br/&gt;&lt;br/&gt;Finally, we consider a mechanism of angular momentum conversion from a transverse optical spin in surface plasmon polaritons (SPPs) to conduction electron spin. Conduction electrons in the metal follow the SPP&#39;s SPP&#39;s transversally spinning electric field, and the resulting orbital motions create inhomogeneous static magnetization in the metal. We will also present an experimental demonstration of the SPPs-induced spin current generation [8]. Such conversion from light to a spin current can be used as a coupler in next-generation spintronic computing with optical data transfer or storage.

**References:**

[1] M. Matsuo et al., Phys. Rev. Lett 106, 076601 (2011)&lt;br/&gt;[2] M. Matsuo et al., Phys. Rev. B 87, 180402(R)(2013); Phys. Rev. B 96,020401(R) (2017). &lt;br/&gt;[3] R. Takahashi et al., Nat. Phys. 12, 52 (2016); Nat. Comm. 11, 3009 (2020).&lt;br/&gt;[4] D. Kobayashi et al., Phys. Rev. Lett. 119, 077202 (2017).&lt;br/&gt;[5] A.Hirohata et al., Sci.Rept. 8, 1974 (2018). &lt;br/&gt;[6] G. Okano et al., Phys. Rev. Lett. 122, 217701 (2019).&lt;br/&gt;[7] D. Oue and M. Matsuo, Phys. Rev. B 101, 161404(R) (2020).&lt;br/&gt;[8] T.J. Wijaya et al., arXiv:2004.12348

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INTERMAG 2021

 Spin transport driven by emergent magnetic fields

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Spin current is a key concept in spintronics. In nonmagnetic metals, the spin-orbit coupling has been utilized for the spin current generation. Recently, an alternative scheme using emergent magnetic fields in moving media is demonstrated [1-5]. In this talk, we will present our recent results on spin transport in nonmagnetic metals driven by a variety of emergent magnetic fields originating from: 1. Liquid metal flow [2,3]. 2. Elastic motion [2,4]. 3. Rigid rotation [1,5]. 4. Non-uniform conductivity of gradient material [6]. 5. Surface plasmon polaritons [7,8]. Firstly, we consider the spin-current generation in moving media. In a moving media, such as elastic materials with the Rayleigh type surface acoustic wave is excited or a pipe flow of liquid metal, the vorticity field couples to conduction electron spin. As a result, the mechanical angular momentum of the moving media is converted into spin angular momentum. In particular, a spin current is generated along the vorticity gradient [2,3,4]. It should be noted that the mechanism using the spin-vorticity coupling is free from the strength of the spin-orbit coupling, and thus, weak spin-orbit coupling materials such as Cu can be utilized for the spin-current source [4]. In a rigid rotating metal, the conventional spin-orbit coupling is augmented due to the emergent magnetic field originating from mechanical rotation [1]. The mechanically induced spin-orbit coupling leads to the spin Hall effect [1]. We introduce a theory of the mechanical analog of the spin Hall effect and an experimental demonstration using magneto-optical detection of spin accumulation under the influence of mechanical rotation [5]. Next, we will discuss our recent experimentally demonstration of the nonreciprocal generation of spin current in a surface-oxidized copper film [6]. This nonreciprocity relies on the transfer of angular momentum from the velocity field of conduction electrons' collective motion. Finally, we consider a mechanism of angular momentum conversion from a transverse optical spin in surface plasmon polaritons (SPPs) to conduction electron spin. Conduction electrons in the metal follow the SPP's SPP's transversally spinning electric field, and the resulting orbital motions create inhomogeneous static magnetization in the metal. We will also present an experimental demonstration of the SPPs-induced spin current generation [8]. Such conversion from light to a spin current can be used as a coupler in next-generation spintronic computing with optical data transfer or storage.

**References:**

[1] M. Matsuo et al., Phys. Rev. Lett 106, 076601 (2011) [2] M. Matsuo et al., Phys. Rev. B 87, 180402(R)(2013); Phys. Rev. B 96,020401(R) (2017). [3] R. Takahashi et al., Nat. Phys. 12, 52 (2016); Nat. Comm. 11, 3009 (2020). [4] D. Kobayashi et al., Phys. Rev. Lett. 119, 077202 (2017). [5] A.Hirohata et al., Sci.Rept. 8, 1974 (2018). [6] G. Okano et al., Phys. Rev. Lett. 122, 217701 (2019). [7] D. Oue and M. Matsuo, Phys. Rev. B 101, 161404(R) (2020). [8] T.J. Wijaya et al., arXiv:2004.12348

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technical paper

I.Introduction Switched reluctance motors (SRMs) inherently have the advantages of simple structure, no mechanical friction, flexible control and long service life so that they have a good application prospect in hybrid electric vehicle, military and rail transit. Bearingless switched reluctance motors (BSRMs) combine the merits of SRMs and magnetic bearings. However, in the traditional BSRMs, double windings are wound on the stator poles to produce suspension force and torque at the same time. It leads to a problem of nonlinear strong coupling between the torque flux and suspension flux. Therefore, a novel three-pole BSRM is presented, which produces torque and radial controllable suspension force. Each torque pole is designed to be two poles in the axial direction, and suspension poles can be designed larger. The torque poles take up less radial space of the stator in order to increase the radial suspension force density. Firstly, the configuration and suspension principle of the novel BSRM are introduced. Then, the mathematical model of radial suspension force calculation is presented by means of equivalent magnetic circuit. Finally, according to the main parameters of the BSRM, the air-gap magnetic fields and radial suspension forces are analyzed by MagNet 3D. The research results verify the performance of the proposed BSRM. II.Configuration and Suspension Principle According to Fig.1, the proposed BSRM consists of two pieces of stator cores with six stator poles, two rotor cores with six rotor poles and two radial magnetized permanent magnets. The stator poles can be divided into torque poles and suspension poles. Different from conventional BSRM, the torque poles are designed to place axially, the width of rotor pole and torque pole is designed to be equal, the width of suspension pole is designed to be larger than that of the rotor pole. Therefore, there is always a rotor pole under the suspension pole when the rotor is rotating. Radial suspension control flux is generated by radial control current, and the bias flux is generated by two permanent magnets, which form a close path through two stator cores and two rotor cores. Torque flux passes through the torque poles, air gaps and rotor poles, which is separated from the control flux. The paths of suspension flux and torque flux are separated. The torque and suspension force are decoupling naturally. Based on the equivalent magnetic circuit analysis, the mathematical models of suspension force are deduced. The radial suspension force can be written as Fj=Fpm+kij×ij where the subscript “j” denotes A, B and C. Fpm is the magnetic attraction force produced by the bias flux at the equilibrium position. kij is the radial force-current stiffness. Fm and kij can be given as Fpm=S×μ0×Fm×Fm÷(4g2) Kij=S×μ0×Fm×N÷(2g2) where μ0 is vacuum permeability. S is radial magnetic pole area. g is radial air gap length. N is number of radial control coils. III.Models, Design and Analysis To analyze the electromagnetic performance of the proposed three-pole BSRM, including magnetic flux distribution and the force-current relationships, the software MagNet is used to build the finite element model. The simulation results are shown in Fig. 2. Fig. 2(a) shows the bias flux distribution of the proposed BSRM. When the rotor is located in the balance position, the air gap bias flux density under three suspension poles is equal. Fig. 2(b) shows the control flux distribution when the maximum suspension force in the X direction is generated .The reluctant flux distribution is shown in Fig. 2(c) and Fig. 2(d). In Fig. 2(c), it can be seen that the air gap flux density increases under pole A and decreases under pole B and pole C, resulting in a suspension force pointing to the positive X direction. Fig. 2(d) shows another case of the reluctant flux distribution. The air gap density increases under pole B and decreases under pole C. It leads to the suspension force pointed to the positive Y direction. Therefore, the correctness of magnetic circuit and suspension mechanism is proved. The relationship between the control current and radial suspension force Fx and Fy can be calculated. Comparison between the simulation value and theoretical value is shown in Fig. 2(e) and Fig. 2(f). In Fig. 2(e), the suspension force in the X direction is produced, when the current changes from 0 to 3 A. When the control current changes from 0 to 3 A, the force-current relationship is shown in Fig. 2(f). Based on the above analysis, the correctness of the mathematical model is proved. Fig. 2(g) shows the fluctuation suspension force Fx and Fy. It can be seen that the force is stable in the rotating condition. IV.Conclusion This paper presents a novel three-pole BSRM with independent torque and suspension force magnetic circuit. The theory analysis and simulation results are verified the electromagnetic performance of the proposed BSRM.

**References:**

[1]J. Ju, H. Zhu and C. Zhao, "Radial Force-Current Characteristic Analysis of Three-Pole Radial-Axial HMB," 2016 IEEE Vehicle Power and Propulsion Conference (VPPC), Hangzhou, 2016, pp. 1-6. [2]R. Zhu, W. Xu, C. Ye, J. Zhu, G. Lei and X. Li, "Design Optimization of a Novel Heteropolar Radial Hybrid Magnetic Bearing Using Magnetic Circuit Model," in IEEE Transactions on Magnetics, vol. 54, no. 3, pp. 1-5, March 2018, Art no. 8201105.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/2ebd4d829e367720548b33bc78b6d169.jpg)

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 Suspension Characteristics for a Novel Three-pole Bearingless Switched Reluctance Motor

I. Intorduction In this paper, a new coupling method for efficient and simple analysis of induction motor is presented. The circuit concept is applied to stator winding and each conductor loop of rotor composed of rotor bar and end ring segment. The flux linkage by magnetic field distribution is used instead of inductance matrix. The flux linkage is calculated using air-gap flux density distributions by unit current in stator winding and rotor bars. Once the field distribution by one coil is calculated by FEM, its result is used for total flux linkage by employing a coordinate transformation. Its numerical results show a good agreement with the existing results. Especially the method is very effective in analyzing the effect of the number of rotor bars. This This method can be used for the analysis of both three-phase induction motors and single-phase induction motors. As the classical theory for operating characteristics of induction motor, there are two main theories: the two-motor theory of two rotating fields and the cross field theory. But they cannot deal the coil distribution and accurate magnetic field distribution, so that the effects of the number of rotor bars is not characterized. On the other hand, its full finite element analysis requires massive calculation time and complex modeling techniques for time-stepping eddy current problem and remeshing problem. In this paper, the circuit concept is applied to the stator winding and the rotor conductor loops composed of rotor bar and end ring segment. The flux linkage obtained from FE field analysis is employed instead of inductance matrix. The flux linkage is calculated using the air gap field distribution by a unit current in stator and rotor bars. The total flux linkage of external circuit equation is easily calculated using superposition of each coil field and a coordinate transformation. That is, this method requires only few field analyses of a unit current of stator and rotor conductor. Once the flux parameters are obtained, the overall motor characteristics such as stator current, rotor bar current, torque are easily calculated in both transient state and steady state. The transient characteristics for the all currents are calculated in a recursive form by using finite time difference scheme. II. Coupling Method Circuit and Flux Distribution The circuit equation of stator winding is represented by convential voltage equation. The flux parameter of magnetic flux linkage is composed of the fields by both the stator winding current and the rotor bar currents. The circuit equation of rotor winding is also expressed by general equation like an Faraday's law. This Faraday formula requires a bar resistance, an endring resistance, and a current of each conductor bars. Also, the distribution of magnetic flux density on the rotor surface is required. Also, the KCL for the rotor bar and end ring is needed. Using the above equation we can calculate output current for the input voltage. The motor torque on the rotor bars can be also calculated from Lorentz force formula by using the resulting currents and magnetic flux density distribution. III. Numerical Applications The proposed algorithm is applied to a single and three phase induction motor. The rotor bar current is obtained as in Fig. 1. The average torque-speed curves according to different rotor bar resistances are shown in Fig. 2. This analysis technique is considered to be very useful to quickly grasp the characteristics in the initial process of designing single-phase and three-phase induction motors.

**References:**

[1] Gyril G. Veinott, E. E., D. Eng., Theory and Design of Small Induction Motors, McGRAW-HILL , 1959, pp. 184-197. [2] N. Sadowski, R. Carlson, S. R. Arruda, C. A. da Silva and M. Lajoic-Mazenc, “Simulation of Single-phase Induction Motor by a General Method Coupling Field and Circuit Equations,” IEEE Trans. on Magnetics, Vol. 31, No. 3, 1995. [3] Sheppard J. Salon, Finite Element Analysis of Electrical Machines, Kluwer Academic Publisher, 1995. [4]D. Kim and B. Kwon, "A Novel Equivalent Circuit Model of Linear Induction Motor Based on Finite Element Analysis and Its Coupling With External Circuits," in IEEE Transactions on Magnetics, vol. 42, no. 10, pp. 3407-3409, Oct. 2006. [5] M. Liu, K. W. Chan, J. Hu, Q. Lin, J. Liu and W. Xu, "Design and Realization of a Coreless and Magnetless Electric Motor Using Magnetic Resonant Coupling Technology," in IEEE Transactions on Energy Conversion, vol. 34, no. 3, pp. 1200-1212, Sept. 2019.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/8f83bc771ba42b168160ed3ac845e9c8.jpg)
Fig. 1 Caculated Rotor Bar Current

![](https://assets.underline.io/uploads/markdown_image/1/image/725ae10d0e8c34dd2ac9ad472179abcb.jpg)
Fig. 2 Torque vs. Speed Characteristic Curve

 Coupling Method of Circuit Equation and Magnetic Field Distribution for Characterization of Induction Motors by Coordinate Transformation

INTRODUCTION Wireless power transfer (WPT) is increasingly popular in many interdisciplinary areas, such as energy encryption and electric vehicles [1]. As the WPT has unique advantages of higher flexibility and no sparking hazard [2], the WPT changes the conventional usage of energy in industry and domestic applications. Recently, a number of efforts have been made to incorporate WPT into electric motors to achieve wireless motor, which is favorable for harsh and watery environments. [3] can be regarded as a landmark paper for proposing dual controller wireless motor, which cascades the traditional motor system in the receiver side of WPT, thus wire abrasion can be avoided in harsh environments. However, motor controller is fragile and not suitable for isolated environments, so WPT with primary-control systems for DC motor [4], switched reluctance (SR) motor [2], and shaded pole induction motor (SPIM) [5] have been studied, which used self-drive circuit to replace the motor controller. However, DC motor suffers from the fragile carbon brushes and commutator, wireless SR motor needs three receivers, and wireless SPIM needs five controlled switches. To solve these problems, this paper proposed a new wireless system with secondary half-bridge inverter for SPIM, thus the number of controlled switches can be eliminated from five to two, and the key is to employ a three-winding transformer. METHODOLOGY Fig. 1 depicts the system configuration, where LT and LR are the inductance of transmitter and receiver, while CT, CT1, and LT1 are the resonant inductances and resonant capacitance to constitute the multiple-frequency resonating compensation (MFRC) network [6] at the transmitter side, and CR, CR1, and LR1 constitute the receiver’s MFRC network; LP, CP, LN, and CN constitute the positive and negative LC tuning circuits, which are resonant at fP and fN, respectively; CL is the filter capacitance of the bridge rectifier; SP and SN comprise the half-bridge inverter to control two primary transmitter windings, namely, positive and negative windings, respectively, and ILP and ILN are used to represent the current of these two windings; VS, VCP, VCN, and VM are adopted to represent the voltage of AC source, CP, CN, and load motor, respectively. It should be mentioned that the switched-capacitor array is adopted in [5], but this compensation suffers from high voltage switching stress. Thus, a specially designed MFRC network is employed in this paper (the design method is detailed in [6]), which can seamlessly compensate the receiver and transmitter at two frequencies without any voltage stress. The working principle is almost the same as [5], as the whole control process can be separated into positive and negative half-cycles, and the control signal for SP and SP are extracted from VCP, VCN, respectively. Taking positive half-cycle as an example, when the primary side transmits the energy at fP, the receiver current mainly flows the positive LC tunning circuit, so VCP is high while VCN is almost zero, thus SP is on, and SN is off. Therefore, by transmitting at fP or fN in turns, the positive and negative windings of the transformer are fed in turns. As the two primary windings of the transformer are reversely winded, AC voltage can be induced in the secondary winding of the transformer. Circuit simulations are carried out to show the feasibility of the proposed system. It should be mentioned that the load motor is replaced by a 120 Ω resistor, which is the equivalent resistance of SPIM in [5], and the other parameters will be given in the full paper. The simulation results are presented in Fig. 2, which depicts the waveforms of power source VS and load voltage VM, as well as the inverter output current ILP and ILN at different speeds. It should be noted that the power source should be higher when transmitting at a higher frequency [5], i.e., fN, in this paper. Consistent with theory analysis, when the system frequency alternatively changes between fP and fN, ILP and ILN correspondingly change, and an AC voltage VM is induced in the secondary side of the transformer to feed the SPIM. Besides, when the system works at rated condition, i.e., the effective value of VM is 110 V, VS is 70 V and 97 V at positive and negative half-cycles, respectively; when the system works at 25 Hz, and the effective value of VM is 55 V, VS becomes 35 V and 50 V at positive and negative half-cycles, respectively. Thus, it can be calculated that VS/VM is around 0.64 and 0.91 at positive and negative half-cycles, respectively. In other words, both the frequency and voltage of the load can be proportionally controlled from the primary side, thus the speed regulation can be achieved. CONCLUSION This paper proposed a novel WPT system for SPIM with a self-drive half-bridge inverter. Compared with former research [5], less controlled switches are applied, thus the proposed system has higher stability and is more suitable for isolated environments. Besides, in order to compensate the transmitter and receiver at two frequencies, a proper MFRC network is employed, which successfully avoids the voltage switching stress. Finally, the simulation results are presented to show system's feasibility and the speed regulation ability, and the experiment will be given in the full paper.

**References:**

[1] M. H. Mahmud, W. Elmahmoud, and M. R. Barzegaran, "Efficient wireless power charging of electric vehicle by modifying the magnetic characteristics of the transmitting medium," IEEE Transactions on Magnetics, vol. 53, no. 6, (2017) [2] C. Jiang, K. T. Chau, and Y. Leung, "Design and analysis of wireless ballastless fluorescent lighting," IEEE Transactions on Industrial Electronics, vol. 66, no. 5, pp. 4065-4074 (2019) [3] M. Sato, G. Yamamoto, D. Gunji, T. Imura, and H. Fujimoto, "Development of wireless in-wheel motor using magnetic resonance coupling," IEEE Transactions on Power Electronics, vol. 31, no. 7, pp. 5270-5278 (2016) [4] C. Jiang, K. T. Chau, and T. W. Ching, "Time-division multiplexing wireless power transfer for separately excited DC motor drives," IEEE Transactions on Magnetics, vol. 53, no. 11 (2017) [5] H. Wang, K. T. Chau, and C. H. T. Lee, "Design, analysis and implementation of wireless shaded-pole induction motors," IEEE Transactions on Industrial Electronics, to be published. [6] Z. Zhang, X. Li, and H. Pang, "Multiple-frequency resonating compensation for multichannel transmission of wireless power transfer," IEEE Transactions on Power Electronics, to be published.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/e4ef9c6a059853c50387e6570fb6a2c4.jpg)
System topology of wireless SPIM for traditional SPIM

![](https://assets.underline.io/uploads/markdown_image/1/image/d561058d1a9dedd8513312decd22dd95.jpg)
Fig. 2 Circuit simulation results at different frequencies. (a) Voltage at 50 Hz. (b) Current at 50 Hz. (c) Voltage at 25 Hz. (d) Current at 25 Hz.

 A Primary-Controlled Wireless Single-Phase Induction Motor Using Secondary Self-Drive Half-Bridge Inverter

I. INTRODUCTION Doubly salient brushless DC (DSBLDC) motor offers the merits of simple structure, low cost, and high reliability because there is no permanent magnet on the rotor. The preformed rectangular wire winding has high filling ratio and excellent heat transfer performance [1], which can greatly improve the performance and fabrication efficiency of DSBLDC motor. Therefore, the DSBLDC motor with rectangular wire winding is applied in harsh operation conditions and low cost applications. The loss of the motor affects both efficiency and the heating of the motor, so the loss analysis is particularly important. At present, the loss analysis of DSBLDC motor mainly focuses on the influence of motor structure and winding form, and the control method is seldom studied. In this paper, the loss of a DSBLDC motor with rectangular wire winding driven by square wave and sinusoidal wave are comparatively studied, and the effect of PWM on motor loss in actual operation is considered. The influence of speed on loss under different driving modes is also studied. The loss of a 4.2kW DSBLDC motor with rectangular wire winding driven by different driving modes has been analyzed. II. MACHINE AND DRIVING MODES Fig. 1(a) shows the configuration of the 12/8-pole DSBLDC motor. The armature winding in the stator adopts rectangular wire winding, as shown in Fig. 1(b). The back electromotive force (BEMF) waveform and its harmonic component of DSBLDC motor are shown in Fig. 2. The BEMF of DSBLDC motor has the second harmonic component, and the BEMF waveform is near-sinusoidal. According to its BEMF characteristic, it can be respectively driven by square wave current or sinusoidal wave current, as shown in Fig. 3. In general, these two driving modes are called BLDC driving mode and BLAC driving mode respectively. Fig. 4 and Fig. 5 show the actual waveforms of phase current and output torque under two driving modes. The influence of pulse-width modulation (PWM) on motor loss should also be considered. By comparing Fig. 4(b) and Fig. 5(b), it can be seen that the output torque characteristic of BLAC mode is obviously better than that of BLDC mode. III. LOSS ANALYSIS AC copper loss and iron loss are the two main parts of the DSBLDC motor loss. AC copper loss consists of DC loss and eddy loss, and iron loss consists of hysteresis loss and eddy loss. Fig. 6 shows the results of loss comparison for the BLDC mode and BLAC mode with ideal and the actual phase current waveform under PWM control. When the effective value of phase current is 24.5A, the DC loss in AC copper loss and the hysteresis loss in iron loss are basically same in each driving mode, while both eddy losses in AC copper loss and iron loss of BLAC mode are less than that of BLDC mode. In addition, the actual PWM control causes high-frequency current ripple, which has more obvious influence on BLDC mode than BLAC mode, making the loss difference between the two driving modes further enlarged. Fig. 7 and Fig. 8 show the curves of the magnetic flux density and loss when the DSBLDC motor is driven by ideal BLDC and BLAC current. AC copper loss and iron loss analysis take point A at the armature winding position and point B at the stator core position as examples respectively. According to the relevant formula, the eddy loss is proportional to the second power of the magnetic density change rate. In BLDC mode, the magnetic flux density changes rapidly during the commutation, resulting in a significant increase of AC copper loss and iron loss. In BLAC mode, the magnetic flux density changes slowly during the whole cycle, so there is no significant increase of loss. The ratio of AC loss to DC loss and iron loss vary with the speed under two driving modes, as shown in Fig. 9. With the increase of the speed, AC copper loss and iron loss in BLDC mode increases faster than that in BLAC mode. IV. CONCLUSION In this paper, the copper loss and iron loss of a DSBLDC motor respectively driven by BLDC and BLAC are analyzed and compared. The output torque characteristic of BLAC mode is better than BLDC mode, and the loss characteristic is also better than BLDC mode. Under the two driving modes, The DC loss in AC copper loss and the hysteresis loss in iron loss are basically the same, but the eddy losses both in AC copper loss and iron loss of the BLAC mode decrease significantly, due to the reduction of magnetic field harmonic content in the motor groove and the iron core. Meanwhile, actual PWM control will relatively increase the loss of the motor, but the influence on the BLAC mode is obviously less than that of the BLDC mode, making the loss advantage of BLAC mode more obvious. The loss increases with the increase of speed, and the increase is less in BLAC mode than in BLDC mode. The simulation results verify the correctness of the loss analysis.

**References:**

[1] Y. Zhao, D. W. Li, T. H. Pei and R. H. Qu, “Overview of the rectangular wire windings ac electrical machine,” in CES Transactions on Electrical Machines and Systems, vol. 3, no. 2, pp.160-169, June, 2019.

**Images:**

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 Influence of Driving Mode on Loss of Doubly Salient Brushless DC Motor With Rectangular Wire Winding

Spin currents in magnetic random access memory (MRAM) devices being developed by the semiconductor industry are generated by passing an electrical current perpendicular to layers that form a magnetic tunnel junction [1]. However, it is now widely appreciated that current flow in the plane of a layer can generate significant spin currents through spin-orbit coupling, as first reported in heavy non-magnetic metal layers (e.g. Pt, Ta & W). In this case, however, the spin polarization is generally confined to the plane of the layers. An important research goal is to create a spin current with an arbitrary polarization, including one with a significant out-of-plane spin polarization to enable efficient switching and displacement of domain walls in perpendicularly magnetized layers. In this talk we discuss spin-orbit induced charge-to-spin conversion in various materials and nanostructures [2] and with magnetic materials. Specifically, we will report our observation of spin torques with a planar Hall effect symmetry from CoNi, with a spin polarization in the magnetization direction of the layer [3]. We found the strength of this effect to be comparable to that of the spin Hall effect in Pt, indicating that the planar Hall effect in ferromagnetic metals holds great promise as a spin current source with a controllable spin polarization direction.

**References:**

 [1] A. D. Kent and D. C. Worledge, Nature Nanotechnology 10, 187 (2015) [2] J-W. Xu and A. D. Kent, Physical Review Applied 14, 014012 (2020) [3] C. Safranski, J. Z. Sun, J-W., Xu and A. D. Kent, Physical Review Letters 124, 197204 (2020)

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 Electrical Generation of Spin Currents

A spin current - a flow of spin angular momentum - can be carried either by spin-polarized free electrons or by magnons, the quanta of spin waves. Traditionally, it was assumed that a spin wave in a magnetic film with spin-sink-free surfaces could transfer energy and angular momentum only along its propagation direction. In this talk, using the data of Brillouin light scattering (BLS) spectroscopy in combination with an extended theory of dipole-exchange spin-wave spectra, I show that in obliquely magnetized magnetic films, the in-plane propagation of spin waves is accompanied by a transverse spin current without any corresponding transverse transport of energy [1]. It is found that in the case of oblique magnetization, the transverse profiles of in-plane-propagating dipole-exchange spin waves are formed by two co-propagating partial waves with opposite group velocities. Their superposition results in a traveling wave pattern, which carries angular momentum and can be treated as a transversal spin current. Its existence is evidenced by the behavior of thermal spectra of magnons in a yttrium iron garnet film measured in a wide range of wavenumbers using our novel wavevector-resolved BLS setup. In the case of an external excitation of the spin-wave modes carrying the transversal spin current, the angular momentum conservation law would lead to mechanical deformations or/and to the rotation of the magnetic film as a whole, which could be detected using the existing methods of spin mechatronics [2]. Furthermore, the presence of the unconventional spin current may be directly electrically detected [1, 3]. We believe that these non-trivial properties of spin-wave modes may be used in the future to control the effects of spin pumping or/and to generate spin currents in nano-scale spintronic signal processing and signal-generating devices. Funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the Research Unit TRR 173–268565370 “Spin+X” (projects B01 and B04), as well as financial support by the European Research Council within the AdG SuperMagnonics, is gratefully acknowledged. The work was also supported in part by the US National Science Foundation, by the US Air Force Office of Scientific Research, and by the Oakland University Foundation.

**References:**

[1] D. A. Bozhko, H. Yu. Musiienko-Shmarova, V. S. Tiberkevich, A. N. Slavin, I. I. Syvorotka, B. Hillebrands, and A.A. Serga, Unconventional spin currents in magnetic films, Phys. Rev. Research 2, 023324 (2020). [2] M. Matsuo, E. Saitoh, and S. Maekawa, Spin-mechatronics, J. Phys. Soc. Jpn. 86, 011011 (2017). [3] P. M. Gunnink, R. A. Duine, and A. Rückriegel, Electrical Detection of Unconventional Transverse Spin Currents in Obliquely Magnetized Thin Films, Phys. Rev. B 101, 220407 (2020).

**Images:**

 Unconventional spin currents in obliquely magnetized magnetic films

Conservation of angular momentum couples spin-currents present in a system with the magnetization dynamics of the ferromagnet. Injecting spin-currents into ferromagnets thereby enables the control of the magnetic state [1]. This forms the basis for many spintronic device applications including spin-transfer torque random access memory [2] and spin torque oscillators [3]. However, the inverse effect where the magnetization generates a spin current also takes place. This can be achieved very efficiently by driving the precession resonantly using an electromagnetic field at GHz frequencies. The same approach has been employed in ferromagnetic resonance spectroscopy experiments for over a hundred years now. Historically ferromagnetic resonance spectroscopy has extensively been used to determine the gyromagnetic ratio, magnetic anisotropies, and exchange stiffness of materials. In recent years the focus has shifted to utilizing broadband ferromagnetic resonance spectroscopy to determine the mechanisms responsible for magnetic damping [4]. In this context the observation that the precession of the magnetization can drive a spin-current into adjacent layers, is known as spin-pumping [5]. In ferromagnetic resonance spectroscopy spin pumping leads to a non-local contribution to the damping in the ferromagnet. This also enables the generation of pure spin currents by exciting the precession of a ferromagnet enabling new functionalities of spintronic devices. Based on this, ferromagnetic resonance spectroscopy can also be used to quantify the relevant parameters governing the spin current generation in these systems, including the interfacial spin mixing conductance [6] and the spin diffusion length [7]. In multilayer systems the spin currents generated at the ferromagnetic resonance frequently also result in the generation of a DC voltage most notably via the inverse spin Hall effect [8]. This has led to the ability to electrically detect ferromagnetic resonance with high sensitivity in small sample volumes, triggering a renewed interest in ferromagnetic resonance spectroscopy. We expect this to continue to enable new insights into the mechanisms foundational to the generation and detection of spin-currents driven by ferromagnetic resonance.

**References:**

[1] J.C. Slonczewski, Current-driven excitation of magnetic multilayers, J. Magn. Magn. Mater. 159, L1 (1996). [2] E. Chen, D.Apalkov, A. Driskill-Smith, et al., Progress and Prospects of Spin Transfer Torque Random Access Memory, IEEE Trans. Magn. 48, 3025 (2012). [3] R. K. Dumas; S. R. Sani; S. M. Mohseni et al., Recent Advances in Nanocontact Spin-Torque Oscillators, IEEE Trans. Magn. 50, 1 (2014). [4] C. K. Mewes, T.Mewes, Relaxation in Magnetic Materials for Spintronics, Handbook of Nanomagnetism, Pan Stanford Publishing, Singapore, p. 71 (2015). Stanford Publishing, Singapore, 2015) p. 71. [5] Y. Tserkovnyak, A. Brataas, G.E.W. Bauer, Enhanced Gilbert Damping in Thin Ferromagnetic Films, Phys. Rev. Lett. 88, 117601 (2002). [6] M. Weiler, M. Althammer, M. Schreier et al., Experimental Test of the Spin Mixing Interface Conductivity Concept, Phys. Rev. Lett. 111, 176601 (2013). [7] A. J. Berger, E. R. J. Edwards, H. T. Nembach et al, Determination of the spin Hall effect and the spin diffusion length of Pt from self-consistent fitting of damping enhancement and inverse spin-orbit torque measurements, Phys. Rev. B 98, 024402 (2018). [8] E. Saitoh, M. Ueda, H. Miyajima, G. Tatara, Conversion of spin current into charge current at room temperature: Inverse spin-Hall effect, Applied Physics Letters 88(18), 182509 (2006).

**Images:**

 Spin Current Generation Driven by Ferromagnetic Resonance

The interconversion between spin, charge, and heat currents is actively studied from the viewpoints of fundamental physics and thermoelectric applications in the field of spin caloritronics. This field is a branch of spintronics, which has developed rapidly since the discovery of the thermo-spin conversion phenomenon called the spin Seebeck effect. In spin caloritronics, various thermo-spin conversion phenomena have subsequently been discovered and magneto-thermoelectric effects, thermoelectric effects unique to magnetic materials, have received renewed attention with the advances in physical understanding and thermal/thermoelectric measurement techniques. The transverse thermoelectric conversion is one of the central topics in spin caloritronics, which is usually realized by the anomalous Nernst effect (ANE) and the anomalous Ettingshausen effect (AEE) in magnetic materials. In ANE (AEE), a heat (charge) current induces a transverse charge (heat) current in the direction perpendicular to the magnetization direction. Based on this symmetry, ANE/AEE exhibits a convenient scaling law that is entirely different from that of conventional thermoelectric effects. Furthermore, the thermoelectric output of ANE/AEE can be actively controlled through the manipulation of magnetization. Thus, ANE (AEE) has the potential to realize simple and versatile thermal energy harvesting or heat-current sensing (thermal energy management) applications. In this talk, we mainly report our recent experimental progress on ANE and AEE [1-5]. We also show a novel approach for transverse thermoelectric generation that exhibits a similar symmetry to ANE but is driven by a different mechanism [6].

**References:**

[1] T. Seki, R. Iguchi, K. Takanashi, and K. Uchida, Appl. Phys. Lett. 112, 152403 (2018). [2] S. Ota et al., Sci. Rep. 9, 13197 (2019). [3] H. Nakayama et al., Appl. Phys. Express 12, 123003 (2019). [4] J. Wang, Y. K. Takahashi, and K. Uchida, Nature Commun. 11, 2 (2020). [5] A. Miura et al., Appl. Phys. Lett. 115, 222403 (2019), Appl. Phys. Lett. 117, 082408 (2020), Phys. Rev. Mater. 4, 034409 (2020). [6] W. Zhou et al., Nature Mater. (in press).

**Images:**

 Transverse thermoelectric conversion based on spin caloritronics

Topology, a mathematical concept, recently became a hot and truly transdisciplinary topic in condensed matter physics, solid state chemistry and materials science. Since there is a direct connection between real space: atoms, valence electrons, bonds and orbitals, and reciprocal space: bands, Fermi surfaces and Berry curvature, a simple classification of topological materials in a single particle picture should be possible [1]. A new class of topological phases that have Weyl points was also predicted in the family that includes NbP, NbAs. TaP, MoP and WP2. [3-5]. Beyond Weyl and Dirac, new fermions can be identified in compounds that have linear and quadratic 3-, 6- and 8- band crossings that are stabilized by space group symmetries [2]. Crystals of chiral topological materials CoSi, AlPt and RhSi were investigated by angle resolved photoemission and show giant unusual helicoid Fermi arcs with topological charges of ±2 [6,7]. In agreement with the chiral crystal structure two different chiral surface states are observed.. As a consequence, the magnetic Heusler compounds have already been identified as Weyl semimetals: for example, Co2YZ [8-11], and Co3Sn2S2 [12-15]. In all these materials the Berry curvature and the classical anomalous Hall (AHE) and spin Hall effect (SHE) are enhanced and interesting for potential applications.

**References:**

[1] Bradlyn et al., Nature 547 298, (2017), Vergniory, et al., Nature 566 480 (2019), [2] Bradlyn, et al., Science 353, aaf5037A (2016). [3] Shekhar, et al., Nat. Phys. 11, 645 (2015) [4] Liu, et al., Nat. Mat. 15, 27 (2016) [5] Gooth et al., Nature 547, 324 (2017) [6] Schröter, et al., Nature Physics 15, 759 (2019) preprint arXiv: 1812.03310 [7] Sanchez, et al., Nature 567, 500 (2019) [8] Kübler and Felser, EPL 114, 47005 (2016) [9] Wang, et al. Phys. Rev. Lett. 117, 236401 (2016) [10] Chang et al., Scientific Reports 6, 38839 (2016) [11] Belopolski, et al., Science 365, 1278 (2019) [12] Liu, et al. Nature Physics 14, 1125 (2018) [13] Liu, et al. Nat. Phys. Nature Physics 14, 1125 (2018) [14] Liu, et al., Science 365, 1282 (2019) [15] Morali, et al., Science 365, 1286 (2019)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/5c96aeda1a535371543bd56d0ea58a5f.jpg)

 Berry curvature and semimetals

Recent theoretical and experimental studies of current-induced manipulation of spin ordering in ferro- (FM) and antiferromagnets (AFM) open up prospects for the development of modern devices for spintronics [1-3]. Antiferromagnets have a number of advantages over ferromagnets that make it possible to fabricate devices with a higher recording density, stability and speed of operation. Thanks to these features, a novel direction of antiferromagnetic spintronics is being actively developing [4,5]. However, the complexity of the experimental study of pure antiferromagnets forces us to seek alternative methods to control and register the Néel ordering. One of the ways is a study of advanced composite materials based on FM/AFM thin films, where the exchange bias (EB) effect at the interface between different magnetic phases opens an additional degree of freedom for modification and measuring the spin structure inside the AFM [6,7]. We present experimental possibility for manipulation of the exchange bias field in the Pt/Co/NiO structure by means of electric current [8]. Our experimental study revealed the mechanism of current-induced transformation in the magnitude and direction of the exchange bias field in this advanced structure. The orientation of the magnetization in FM layer plays a decisive role on direction of exchange bias and the effect of the current is reduced by heating in the investigated structure. Combination of domain structure in FM and influence of current with certain amplitude allows making different distributions of the exchange bias field strength inside the structure. For example, an EB field profile of “Min-Max-Min” type is shown in Fig. 1(c). A domain structure of FM for this case was obtained in the coercive force during remagnetization (see Fig. 1(a)). Hysteresis loops for the regions with Max and Min exchange bias fields are presented in Fig. 1(c). Another interesting EB distribution is shown in Fig. 1(e). The corresponding EB field profile of “Zero-Max-Zero” type could be used to control the nucleation centers of bubble skyrmions and pinning of domain walls. The presented results are useful not only for condensed matter physics in general, but also, for various practical applications in spintronics. Authors acknowledge the financial support of the Russian Ministry of Education and Science under the state task (0657-2020-0013), the Russian Foundation for Basic Research (grant 19-02-00530) and RSF-NSFC grant 21-42-00041. A.G. Kolesnikov thanks the scholarship of President of the Russian Federation for young scientists and graduate students (SP-350.2019.1). Xiufeng Han and Caihua Wan appreciate supports from the National Natural Science Foundation of China [NSFC, Grant No. 51831012, 51620105004， 11974398 and 12061131012] and Beijing Natural Science Foundation (Grant No. Z201100004220006).

**References:**

[1] A. Hirohata, K. Yamada, Y. Nakatani, I.-L. Prejbeanu, B. Diény, P. Pirro, B. Hillebrands, Journal of Magnetism and Magnetic Materials 2020, 509, 166711. [2] S. A. Wolf, A. Y. Chtchelkanova, D. M. Treger, IBM Journal of Research and Development 2006, 50, 101. [3] X. Li, J. Yang, National Science Review 2016, 3, 365. [4] T. Jungwirth, X. Marti, P. Wadley, J. Wunderlich, Nature Nanotechnology 2016, 11, 231. [5] V. Baltz, A. Manchon, M. Tsoi, T. Moriyama, T. Ono, Y. Tserkovnyak, Reviews of Modern Physics 2018, 90, 015005. [6] J. Nogués, I. K. Schuller, Journal of Magnetism and Magnetic Materials 1999, 192, 203. [7] P.-H. Lin, B.-Y. Yang, M.-H. Tsai, P.-C. Chen, K.-F. Huang, H.-H. Lin, C.-H. Lai, Nature Materials 2019, 18, 335. [8] M.E. Stebliy, A.G. Kolesnikov, M.A. Bazrov, M.E. Letushev, A.V. Ognev et al., Applied Physics Letters 2021, 10.1063/5.0035667.

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/9854cc6e888a32cbee26d2d230c5527b.jpg)
Fig. 1. (a) Illustration of the magnetic structure of the Hall bar, divided into three domains, using a Kerr microscope. (b) The graph shows the magnetic hysteresis loops recorded from the corresponding regions after passing a 30 mA pulse through the structure. (c) The exchange bias field profile. (d) Magnetic structure containing multiple isolated domains selected in the process of magnetization reversal. (e) The graph shows the profile of the exchange bias field after passing the current pulse.

Spin transport driven by emergent magnetic fields

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Spin transport driven by emergent magnetic fields

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