Nanowire Spin-Valves for Antiferromagnet Spintronics

该奖项是根据2009年美国复苏和再投资法案(公法111-5)资助的。自旋电子学的新兴领域已经给信息技术带来了革命性的变化，特别是在过去十年中磁记录面密度的爆炸性增长。自旋电子学的核心是自旋阀，它允许低磁场应用和自旋转移扭矩(STT)效应，允许局部电子操纵磁状态。它们支持大量基于自旋的迷人电子应用，从快速、可扩展、非易失性和高能效的磁随机存取存储器，到基于磁区墙的逻辑和可调高频STT振荡器。到目前为止，STT效应一直只在铁磁体中被研究，直到最近提出了基于反铁磁体的STT效应的理论建议。PI的目的是研究多层纳米线中的新型AF-STT效应，构建一种新型的基于纳米线的自旋阀，用于AF自旋电子学的探索。本研究的技术价值在于：自旋阀将通过电化学沉积被结合到纳米线中。纳米线的晶体结构，特别是AF组件的晶体结构将得到优化。定义良好的结构确保了均匀的电流密度，并允许定量测量交换偏置漂移来测量AF-STT。在纳米线阵列和单个纳米线中，将研究电流密度、方向和温度对AF-STT的影响。磁化反转机制和不可逆电阻跳跃之间的关联将用一阶反转曲线方法和时间分辨磁光克尔效应的超快动力学研究来检验。最后，通过X射线磁性圆二色性和线性二色性的研究，探讨了AF界面磁结构变化的直接证据。这些研究不仅将对AF-STT效应进行系统和总结的论证，而且将促进对STT效应的基本认识，并为自旋电子学的探索开辟全新的材料和机制类别。多层自旋阀纳米线也可以作为MR传感器和MRAM元件的大规模并行阵列的原型。这项研究的更广泛影响包括技术进步、学生教育和培训，以及与普通公众的接触。拟议的用于AF-STT研究的多层自旋阀纳米线将具有深远的技术影响，因为自旋阀和STT都是现代自旋电子器件的核心。拟议的项目还将对教育和培训产生广泛影响。参与的研究生将极好地接触到大学和国家实验室的研究环境。该项目还将涉及本科生，特别是那些有志于从事教学事业的学生，以及高中生。在学生培训中将强调演示技能。这些研究工作将被整合到课程开发中，并帮助扩大本科生实验室课程和研究生课程。计划开展外联活动，包括积极参加纳米科学非正式科学教育网络。

"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.