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

为了适应对计算能力不断增长的需求，人们一直在努力寻找快速节能的新型存储器。磁性随机存取存储器，利用磁性来存储信息，用电来读取/写入信息，是新一代存储器的潜在候选者，因为磁性本质上是非易失性的，并且开关速度快。主要的技术挑战是减少在磁性随机存取存储器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，即电子自旋流，通过特殊设计的自旋方向来切换磁化。这项工作将为如何从磁性结构中产生垂直自旋提供革命性的信息，这将显著降低具有垂直磁化的磁性随机存取存储器的功耗。这项研究的结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很有前途的方法，可以将电流转换为可以有效地切换磁化的自旋电流。然而，迄今为止，自旋轨道效应产生的自旋电流受到薄膜几何形状的限制，因此只能在平面内极化。使用平面内极化自旋电流来切换垂直磁化是低效的，由于其可扩展性和热稳定性，在存储器的应用中具有技术上的吸引力。在本提案中，研究者计划探索利用铁磁结构中的自旋轨道效应产生垂直极化自旋电流，这是基于铁磁对自旋方向提供额外控制的假设。两种互补结构将被研究：自旋滤波，其中自旋极化与磁化对齐，自旋旋转，其中自旋极化围绕磁化旋转。该项目利用灵敏的磁光克尔效应磁强计和基于铁磁共振的磁强计在检测磁化自旋扭矩方面的独特专业知识。本课题的具体任务是：(1)量化两种铁磁结构产生垂直极化自旋电流的效率；(2)设计快速开关磁化的高效开关装置。这项研究还将为磁性结构的综合自旋轨道效应提供重要的见解。

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.