EAGER-Generation of Perpendicularly Polarized Spin Current from the Spin-Orbit Effects in Ferromagnetic Thin Film Structures for Memory Applications

为了适应计算能力的不断增长的需求，已经在寻找快速且节能的新型存储器方面做出了巨大努力。磁性随机存取存储器利用磁性存储信息，利用电读写信息，具有磁性非易失性和开关速度快的特点，是新一代存储器的潜在候选者。主要的技术挑战是减少在磁性随机存取存储器的写入过程中切换磁化所需的能量。该项目旨在探索一种有效的方法，通过使用自旋电流来切换磁化，即电子自旋流，具有特殊设计的自旋方向。这项工作将提供有关如何从磁性结构产生垂直自旋的变革性信息，这将显着降低具有垂直磁化的磁性随机存取存储器的功耗。这项研究的成果将导致数据存储和信息技术的重大进步。自旋轨道效应已被证明是一种有前途的方式来将电流转换成自旋电流，可以有效地切换磁化。然而，到目前为止，由自旋-轨道效应产生的自旋电流受到薄膜几何形状的约束，因此仅在平面内极化。使用平面内极化自旋电流来切换垂直磁化是低效的，这在存储器的应用中由于其可扩展性和热稳定性而在技术上是有吸引力的。在这项提案中，研究人员计划探索使用铁磁结构中的自旋轨道效应产生垂直极化的自旋电流，这是基于铁磁性对自旋取向提供额外控制的假设。两个互补的结构将被调查：自旋过滤，其中的自旋极化是对齐的磁化，和自旋旋转，其中的自旋极化旋转的磁化。该项目利用独特的专业知识，使用灵敏的磁光克尔效应磁力测量和铁磁共振磁力测量来检测磁化的自旋扭矩。该项目的具体任务是（1）量化两种铁磁结构中产生垂直极化自旋电流的效率和（2）设计具有快速切换时间的高效磁化切换器件。这项研究也将提供重要的见解，从磁结构的综合自旋轨道效应。

To accommodate the ever-increasing demand of computational power, there has been a great effort in searching for new types of memories that are fast and energy-efficient. Magnetic random access memory, which uses magnetism to store information and electricity to read/write information, is a potential candidate as the new generation of memory because magnetism is intrinsically non-volatile and switches fast. The main technical challenge is to reduce the amount of energy it takes to switch the magnetization in the writing process of the magnetic random access memory. This project aims to explore an efficient way to switch the magnetization by using a spin current, i.e. a flow of electron spins, with a specially engineered spin orientation. This work will provide transformative information on how to generate perpendicular spins from magnetic structures, which will significantly lower the power consumption in magnetic random access memories with perpendicular magnetizations. The outcome from this research will lead to a significant advance in data storage and information technologies. The spin-orbit effects have been demonstrated to be a promising way to convert an electric current into a spin current that can efficiently switch a magnetization. However, thus far the spin currents generated by the spin-orbit effects are constrained by thin film geometries and therefore are only polarized in-plane. It is inefficient to use an in-plane polarized spin current to switch a perpendicular magnetization, which is technically attractive in the application of memories due to their scalability and thermal stability. In this proposal, the investigator plan to explore the generation of a perpendicularly polarized spin current using the spin-orbit effects in ferromagnetic structures, which is based on the hypothesis that the ferromagnetism provides an additional control on the spin orientation. Two complementary structures will be investigated: the spin filtering, where the spin polarization is aligned with the magnetization, and spin rotation, where the spin polarization is rotated about the magnetization. This project leverages on unique expertise in detecting the spin torque on magnetization using the sensitive magneto-optic-Kerr-effect magnetometry and ferromagnetic resonance-based magnetometry. The specific tasks in the project are (1) quantifying the efficiency to generate perpendicularly polarized spin current in the two ferromagnetic structures and (2) designing efficient device for switching magnetization with a fast switching time. This study will also provide important insights in the comprehensive spin-orbit effects from magnetic structures.