Design of Rotor Magnetic Barrier Structure of Built-in Permanent Magnet Motor Based on Taguchi Method

In this paper,a 20kW vehicle built-in permanent magnet synchronous motor is taken as an example,and a magnetic barrier structure is added to the rotor of the motor to solve the uneven saturation problem of the rotor side magnetic bridge.This structure improves the air-gap flux density waveform of the motor by influencing the internal magnetic flux path of the motor rotor,thus improving the sine of the no-load back EMF waveform of the motor and reducing the torque ripple of the motor.At the same time,Taguchi method is used to optimize the structural parameters of the added magnetic barrier.In order to facilitate the analysis of its uneven saturation phenomenon and improve the optimization effect,a simple equivalent magnetic network(EMN)model considering the uneven saturation of rotor magnetic bridge is established in this paper,and the initial values of optimization factors are selected based on this model.Finally,the no-load back EMF waveform distortion rate,torque ripple and output torque of the optimized motor are compared and analyzed,and the influence of magnetic barrier structure parameters on the electromagnetic performance of the motor is also analyzed.The results show that the optimized motor can not change the output torque of the motor as much as possible on the basis of reducing the waveform distortion rate of no-load back EMF and torque ripple.

Spin-dependent transport for a two-dimensional electron gas with magnetic barriers

The spin-dependent conductance and magnetoresistance ratio （MRR） for a semiconductor heterostructures consisting of two magnetic barriers with different height and space have been investigated by the transfer-matrix method. It is shown that the splitting of the conductance for parallel and antiparallel magnetization configurations results in tremendous spin-dependent MRR, and the maximal MRRs reach 5300% and 3800% for the magnetic barrier spaces W = 81.3 and 243.9 nm, respectively. The obtained spin-filtering transport property of nanostructures with magnetic barriers may be useful to magnetic-barrier-based spintronics.

Wave-vector filtering effect of the electric-magnetic barrier in HgTe quantum wells

Because of the helicity of electrons in HgTe quantum wells（QWs） with inverted band structures,the electrons cannot be confined by electric barriers since electrons can tunnel the barriers perfectly without backscattering in the HgTe QWs.This behavior is similar to Dirac electrons in graphene.In this paper,we propose a scheme to confine carriers in HgTe QWs using an electric-magnetic barrier.We calculate the transmission of carriers in 2-dimensional HgTe QWs and find that the wave-vector filtering effect of local magnetic fields can confine the carriers.The confining effect will have a potential application in nanodevices based on HgTe QWs.

Low frequency noise in asymmetric double barrier magnetic tunnel junctions with a top thin MgO layer

Low frequency noise has been investigated at room temperature for asymmetric double barrier magnetic tunnel junctions（DBMTJs）, where the coupling between the top and middle CoFeB layers is antiferromagnetic with a 0.8-nm thin top Mg O barrier of the CoFeB/MgO/CoFe/CoFeB/MgO/CoFe B DBMTJ. At enough large bias, 1/f noise dominates the voltage noise power spectra in the low frequency region, and is conventionally characterized by the Hooge parameter αmag.With increasing external field, the top and bottom ferromagnetic layers are aligned by the field, and then the middle free layer rotates from antiparallel state（antiferromagnetic coupling between top and middle ferromagnetic layers） to parallel state. In this rotation process αmag and magnetoresistance-sensitivity-product show a linear dependence, consistent with the fluctuation dissipation relation. With the magnetic field applied at different angles（θ） to the easy axis of the free layer,the linear dependence persists while the intercept of the linear fit satisfies a cos（θ） dependence, similar to that for the magnetoresistance, suggesting intrinsic relation between magnetic losses and magnetoresistance.