Nonequilibrium Phenomena in Novel Magnetic Materials

提出的研究重点是磁化动力学的各个方面，这发生在几纳秒后，磁系统被逐出其平衡状态。研究成果解决了从基本问题“磁性元件的磁化可以多快切换？”到应用相关问题“如何操纵自旋以应用于高性能/高密度/低能耗的磁电子器件？”

The proposed research is focused on various aspects of magnetization dynamics, which occurs within a few nanoseconds after the magnetic systems are driven out of their equilibrium states. The research outcomes address the issues ranging from the fundamental question "How fast can the magnetization in magnetic elements be switched?" to the application-related problem "How to manipulate spins for the application of high-performance/high-density/low energy-consuming magentoelectronic devices?". One of the research objectives is to explore novel ferromagnetic materials for large perpendicular magnetic anisotropy. Such materials are being extensively studied due to their importance in spintronics applications like magnetic random access memory and high-density magnetic storage. We will investigate the magnetic properties of perpendicularly magnetized Mn-based Heusler alloys, in which the precessional dynamics will be probed using time-resolved magneto-optics with temporal resolution of sub-picosecond. The proposed research also includes the study of the dynamic process of the spin reorientation transition in MnAl thin films. The vortex dynamics excited by spin-polarized current is also of interest. Previously, we have reported on the spin-transfer torque effect in NiFe/Cu/Co circular nanopillars, in which the vortex chirality can be controllably switched by injecting current pulses. Recently, we have successfully fabricated such nanomagnets through an international collaboration. The details of the vortex dynamics, such as excitation of spin-wave eigenmodes, will be investigated using high-frequency magnetoresistance measurement. From an application point of view, the research outcome may lead to an opportunity to implement the vortex nanopillars in memory device applications, in which vortex states with controllable chirality switching may be used as memory bits. Complementary to the experiments, detailed numerical modeling will be performed in order to elucidate the spin-transfer torque induced magnetization dynamics and also to accurately predict the magnetization process in above described nanoelements to improve the performance of proposed spintronics devices.