The objective of this research is to engineer thin film spintronic devices based on a dynamic magnetic proximity effect. A non-zero spin-polarization will be induced in a non-magnetic material by reflection of conduction electrons off the interface of an insulating magnetic material. The approach is to fabricate non-magnetic-conductor/magnetic-insulator structures completely in situ, then probe the resulting spin-polarized current via three complementary techniques: tunneling magnetoresistance, tunneling spin polarization, and x-ray magnetic circular dichroism. Trilayer device structures with independently addressable magnetic layers will also be explored.
Intellectual Merit: This project may spearhead a paradigm shift for all-electrical spintronics. Present efforts focus on injecting spins from ferromagnets into non-magnetic materials. However, spin-injection has crippled progress, particularly for semiconductor-based devices. The proposed devices induce a spin-polarization in a non-magnetic conduction channel by reflection off an insulating magnetic gate, thereby obviating the difficulties of injection. This project will develop the building blocks for a series of more complex device architectures able to deliver electrically tunable spin-polarized currents.
Broader Impacts: This transformational research may ease the integration of spintronics with existing back-end semiconductor processing, thereby substantially reducing barriers to commercial spintronics. This program integrates teaching and multidisciplinary training of undergraduate and graduate students, including those from under-represented groups, by unifying physics, engineering, and materials concepts, and by developing hands-on spintronics experiments for high school and undergraduate laboratories. This work enhances infrastructure via a new collaboration between the University of South Florida and the Advanced Light Source.
We discovered new ways to prepare an important magnetic material in thin film form and incorporate these in to prototype spin-electronics devices, and studied how this material behaves in a wide range of temperatures. We discovered that electrons can become polarized by reflecting off the surface of magnetic insulators. This was demonstrated at room temperature using a magnetic structure known as a spin valve, and at very low temperatures using the interaction of electrons with superconductors. A class of modern electronics device depends on quantum mechanical tunneling of electrons from one material to another. We showed that implementing continuous and discrete tunnel barrier height distributions enables straightforward modeling of multiple phenomena of importance to realistic tunneling devices. A subclass of tunneling devices is the spin filter tunnel barrier. This type of barrier is magnetic, and allows spin polarized electronic current to be generated using non magnetic materials. Our modeling showed how interface roughness and material thicknesses are critical to spin filter materials. Tunneling usually requires thin barriers, but our work shows that spin filtering effects may not be seen using ultra thin barriers. This work may lead to the discovery of more materials that can serve as spin filters. A novel spin electronic phenomenon known as spin transfer torque enables one magnetic material to have its magnetization reversed by the flow of a current. In the context of such spin torque devices, we showed that adding nitrogen to copper may be a useful way to improve threshold currents, power requirements, and device reliability. A class of high frequency magnetic sensors is based on the magnetoimpedance effect. We showed that interface engineering can improve such sensors. A US Patent application resulted from this work. Collaborations leveraged to support this project included partners from: the University of Texas at Austin, Miami University in Ohio, Argonne National Laboratory, and the Naval Research Laboratory. We developed a literature searching learning module designed to help young scientists learn most efficiently how to find quality scientific articles. This work has been incorporated into undergraduate and graduate programs across the USA, and has even been used in Europe. This work supported in part or in whole the education through research of four graduate students (one African American, one female), six undergraduates (one undergraduate Hispanic female, one undergraduate Hispanic male), and two high school students (admitted to U. Washington and U. Maryland). Outreach efforts included laboratory tours to middle and high school students, as well as community college students.
