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.
