Magnetization State Manipulation Research Articles

Variable-Flux Machine Torque Estimation and Pulsating Torque Mitigation During Magnetization State Manipulation

This paper focuses on dynamic control, under loaded conditions, of the magnetization state of suitably designed variable-flux (VF) permanent-magnet (PM) machines. Such VF-PM machines have been shown to achieve low loss operation over a wide range of load and speed. For this type of machine, the PM flux linkage varies during the magnetization manipulation process. Published magnetization techniques have occurred at zero load conditions and thus did not generate torque pulsations. However, under loaded conditions, the existing methods would produce unwanted torque pulsation. This paper proposes a parameter insensitive method to solve this issue. This method generates a decoupling current command that is calculated from accurately estimated stator flux linkage. Accurate flux estimation, i.e., insensitive to inductance saturation and PM flux linkage variation (e.g., temperature or magnetization level) is achieved by using the voltage disturbance estimated by a closed-loop stator current vector observer. In both simulations and experiments, it is shown that even during magnetization processes under loaded conditions, the flux can be estimated correctly, and smooth torque output can be achieved.

Manipulation of magnetic state in nanostructures by perpendicular anisotropy and magnetic field

We investigate the transitions of spin configurations in ultrathin nanostructures by tuning the perpendicular anisotropy (Kz) and out-of-plane magnetic field (H), using the Monte Carlo simulation. It is revealed that enhancing the anisotropy Kz can drive the evolution of in-plane vortex state into intriguing saturated magnetization states under various H, such as the bubble domain state and quadruple-block-domain state etc. The spin configurations of these states exhibit remarkable H-dependence. In addition, the strong effects of geometry and size on the spin configurations of nanostructures are observed. In particular, a series of edged states occur in the circular disk-shaped lattices, and rich intricate saturated magnetization patterns appear in big lattices. It is suggested that the magnetic states can be manipulated by varying the perpendicular anisotropy, magnetic field, and geometry/size of the nanostructures. Furthermore, the stability (retention capacity) of the saturated magnetization states upon varying magnetic field is predicted, suggesting the potential applications of these saturated magnetization states in magnetic field-controlled data storages.

電子顕微鏡による電流励起磁化ダイナミクスの観察

Manipulation of magnetic states in ferromagnetic materials using spin-polarized current has attracted much attention because of a wide range of possible spintronic applications. For well controlled magnetic domain manipulation, we microscopically investigate the current-excited magnetization dynamics in narrow Permalloy wires by means of Lorentz microscopy and electron holography, together with the results of simultaneous transport measurements. Current pulses are found to induce a variety of magnetization dynamics below the Curie temperature and a detailed structural evolution of the magnetization is presented as a function of applied current density. We discuss probable mechanism of observed features of the current-excited magnetization dynamics.