Nanowire Spin-Valves for Antiferromagnet Spintronics

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"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."The emerging field of spintronics has already revolutionized information technology, particularly in the explosive growth of the magnetic recording areal density over the past decade. At the heart of spintronics are spin-valves that permits low magnetic field applications and a spin-transfer torque (STT) effect that allows local electrical manipulation of magnetic states. They enable a host of fascinating spin-based electronics applications, from fast, scalable, non-volatile and energy-efficient magnetic random access memory, to domain wall based logic and tunable high frequency STT oscillators. The STT effect has so far been exclusively studied in ferromagnets, until the recent theoretical proposals of antiferromagnet (AF) based STT effect. The PI aims at investigating the novel AF-STT effect in multilayered nanowires and building a novel type of nanowire based spin-valves for AF spintronics explorations. The technical merits of the research are as follows. Spin-valves will be incorporated into nanowires by electrochemical deposition. Crystal structures of the nanowires, particularly those of the AF components, will be optimized. The well-defined structure guarantees uniform current density and allows quantitative measures of the exchange bias shift to gauge the AF-STT. The effect of current density, direction, and temperature on the AF-STT will be investigated, in both arrays of nanowires and a single nanowire. Correlation between magnetization reversal mechanisms and irreversible resistance jumps will be examined using a first order reversal curve method as well as ultrafast dynamic study by time-resolved magneto-optical Kerr effect. Finally, direct evidence on the modification of the AF interfacial magnetic microstructure will be probed by x-ray magnetic circular and linear dichroism. These studies will not only systematically and conclusively demonstrate the AF-STT effect, but also advance the basic understanding of the STT effect and open up whole new classes of materials and mechanisms for spintronics explorations. The multilayered spin-valve nanowires also serve as prototype massively parallel arrays of MR sensors and MRAM elements. The broader impacts of the research include technological advances, student education and training, and outreach to the general public. The proposed multilayered spin-valve nanowires for AF-STT studies will have far reaching technological impacts since both spin-valve and STT are at the heart of modern spintronic devices. The proposed project will also have broad impacts on education and training. Graduate students involved will receive excellent exposure to university and national laboratory research environment. This project will also involve undergraduate students, especially those aiming at a teaching career, as well as high school students. Presentation skills will be emphasized in student training. The research efforts will be integrated into curriculum development and help to expand an undergraduate lab course and a graduate course. Outreach activities including active participation in the Nanoscience Informal Science Education (NISE) network are planned.