CAREER: Novel Spintronics Devices based on symmetry-broken systems

自旋是电子的固有特性，使其表现得像一个微型磁铁，可以通过电流在材料中移动。自旋电子学旨在利用电子自旋来连接不同的物理领域，如电、磁、光学等。自旋电子学最早的应用之一是在硬盘驱动器读磁头上，它显著提高了存储密度，加速了计算机和互联网的发展。近年来，自旋电子学的新发展导致了大量的新应用，例如快速且非易失性的磁性随机存取存储器，以及功能强大且经济的太赫兹脉冲发生器。这些应用都是基于电流和电子自旋之间的相互作用。这个CAREER项目旨在通过使用具有破对称性的新型材料/结构来开发和理解电流和电子自旋之间的新相互作用。与传统的自旋电子学设备相比，对称破缺系统的使用将解锁新的功能。这项研究的成功将加速下一代非易失性存储器和逻辑器件的发展，提高能源效率，并激发新的自旋电子学器件的发展，如光螺旋和表面磁化探测器。教学和推广活动包括利用拟议的研究，PI将设计本科和研究生课程模块，通过使用实验室工具和智能手机应用程序集成磁学实践实验。PI将继续举办在线自旋电子学研讨会和在线教程，这将成为教育和吸引年轻科学家的平台。在自旋-轨道相互作用的驱动下，常规非磁性材料中电流与自旋电流的相互转换一般遵循自旋霍尔对称，即电流、自旋电流和自旋取向相互正交。这种对称性限制使得在薄膜器件中产生面外极化自旋电流具有挑战性，这在实际磁存储应用中是非常需要的。这个CAREER项目探索了电流和自旋电流在对称破缺系统中具有新对称性的相互转换。要探索的两大类对称破缺系统是(1)磁有序异质结构和(2)微结构不对称的非磁性薄膜。通过互补的光学和电学技术，测量施加在相邻磁层上的自旋轨道扭矩，从而检测自旋电流产生的对称性和效率。这一测量结果将为选择和优化产生面外极化自旋电流的最有效系统提供指导。利用优化后的系统，对垂直磁化的电流感应阻尼调制和无场开关进行了实验研究。此外，在光学自旋抽运和自旋霍尔磁阻方面，还将实验探索基于非常规对称自旋-电荷转换的新现象。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Spin is an intrinsic property of the electron, causing it to behave as a miniature magnet that can be moved in materials by an electric current. The field of spintronics aims to harness the electron spin to connect different physics fields of electricity, magnetism, and optics, etc. One of the first applications of spintronics was in the hard disk drive read head, which significantly increased storage density, accelerating the development of computers and the internet. In recent years, new developments in spintronics have led to a plethora of novel applications, such as magnetic random access memories that are fast and non-volatile, and Terahertz pulse generators that are powerful and economic. These applications are all based on the interactions between electric currents and electron spins. This CAREER project aims to develop and understand new interactions between electric currents and electron spins by using novel materials/structures with broken symmetries. Compared to traditional spintronics devices, the use of symmetry-broken systems will unlock new functionalities. Success in this proposed research will expedite the development of next-generation non-volatile memory and logic devices with enhanced energy efficiency and inspire development of new spintronics devices such as light helicity and surface magnetization detectors. The teaching and outreach activities include by leveraging the proposed research, the PI will design undergraduate and graduate course modules that integrate hands-on experiments in magnetism by using lab tools as well as smartphone applications. The PI will continue to host online spintronics seminars and online tutorials, which will serve as a platform for educating and attracting young scientists. Driven by the spin-orbit interaction, the interconversion between electric current and spin current in conventional nonmagnetic materials generally follows the spin Hall symmetry, such that the electric current, spin current and spin orientation are all orthogonal to each other. This symmetry restriction makes it challenging to generate out-of-plane polarized spin current in thin film devices, which is highly desired in practical magnetic memory applications. This CAREER project explores interconversions between electric current and spin current with new symmetries in symmetry-broken systems. The two main categories of symmetry-broken systems to be explored are (1) magnetically-ordered heterostructures and (2) nonmagnetic films with microstructural asymmetry. The symmetry and efficiency of spin current generation will be detected by measuring spin-orbit torque exerted onto a neighboring magnetic layer via complementary optical and electrical techniques. This measurement will serve as a guideline to select and optimize the most efficient systems to generate out-of-plane polarized spin current. Using the optimized system, current-induced damping modulation and field-free switching of perpendicular magnetization will be experimentally studied. In addition, new phenomena based on the spin-charge conversion with unconventional symmetry will also be experimentally explored in optical spin pumping and spin Hall magnetoresistance.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.