Spin Transport Studies In Band And Interface Tailord Materials: Towards Total Spin Polarization For Spin Electronics

非技术：由于基础研究的进步以及对超高密度磁存储需求的不断增长，最近人们对基于电子自旋输运的设备产生了巨大的兴趣。在这个由美国国家科学基金会赞助的项目中，我们将研究与此相关的基本性质以及磁性的应用方面，预计将对该领域的基础水平以及未来基于自旋的信息技术产生影响。为了实现这一目标，将对几个新系统进行自旋极化输运研究，并了解和操纵自旋极化，P（输运电子自旋极化的程度），并开发“定制”材料。例如，我们将探索钴-铁-硼合金体系，该体系最近展示了非常大的隧道磁电阻（TMR）值（越高越有用），以实现更高的P和TMR值。这种材料系统在很大程度上仍未被探索，这项研究应该为P接近100%的候选材料开辟道路，没有半金属铁磁体的界面问题。铁磁体-绝缘体界面键合对于控制p的大小至关重要。我们将致力于控制更高p的这种键合。用精心定制的材料和界面在纳米尺度上制造结构的可能性将使我们能够创造出具有合适性能的新材料。特别是，通过量子岛的自旋极化输运产生了新的效应，如自旋共振隧道效应，这可以大大提高TMR（在我们的实验室观察到），并有可能制造自旋晶体管。通过这一推广计划对学生进行科学教育将继续有效地满足国家对加强科学教育的需要。为了延续这一传统，除了培养研究生和博士后研究人员外，本科生和高中生也广泛参与这项研究。这将极大地有利于这些年轻一代的训练，为未来的旋转纳米技术。技术：在这个国家科学基金会支持的个人项目中，提出了一系列研究，重点关注磁性的基本特性和应用方面，这将有利于基础水平和未来的基于自旋的信息技术。我们将对几个新系统的自旋极化输运进行研究，以了解和操纵自旋极化(P)，这是未来自旋器件所必需的。我们的目标是控制这种键合并探索新的隧道势垒以实现更高的P，包括对Co-HfO2体系的探索，预计P=100%。自旋过滤器隧道是少数几种接近100% P的方法之一（我们小组过去已经证明了这一点），我们将探索在LHe温度以上实现P=100%的方法。基于组成CoB和FeB合金的电子结构，我们认为有可能“定制”(Co,Fe)-B波段杂化，以获得更高的P和隧道磁阻（TMR）值。这种材料系统在很大程度上仍未被探索，应该为高P的候选材料开辟道路，没有半金属铁磁体的界面问题。利用纳米尺度的维度，特别是通过量子岛的自旋极化输运，可以产生新的效应，如自旋共振隧道效应，可以大大提高TMR，正如我们在实验室中观察到的那样。利用非平衡自旋积累和弹道自旋输运的双磁隧道结将被探索，具有自旋晶体管等新型器件的潜力。和过去一样，除了研究生、博士后研究人员和访问科学家外，本科生和高中生也参与了这项研究计划。通过这一推广项目对学生进行科学教育将继续有效地满足国家对科学教育的需求。

Nontechnical:Enabled by advances in basic research as well as driven by a rising demand for ultra-high density magnetic storage, there is an enormous interest of late in devices based on electron spin transport. In this NSF sponsored project we will investigate fundamental properties as well as applied aspects of magnetism related to this, with an expected impact on the field at the basic level as well as the future spin-based information technology. To reach this goal, spin-polarized transport studies of several novel systems will carried out, and to understand and manipulate the spin polarization, P (the degree to which transport electrons are spin polarized), and develop "tailored" materials. For example, we will explore the Cobalt-Iron_Boron alloy system, which recently demonstrated very large tunneling magnetoresistance (TMR) values (the higher it is the more useful for application), to achieve even higher P and TMR values. This material system remains largely unexplored and this study should open the way for candidate materials where P approaches 100%, without the interface problems of a half metal ferromagnet. Ferromagnet-insulator interface bonding is crucial in controlling the magnitude of P. We will aim at controlling this bonding for higher P. The possibility to make structures on a nanometer scale with well-tailored materials and interfaces will allow us to create new materials that show suitable properties. In particular, spin-polarized transport through quantum islands gives rise to novel effects such as spin-resonant tunneling, which can greatly enhance the TMR (observed in our laboratory) with the possibility of making spin transistors. The education of students in science through this outreach program will continue in an effective way to meet the national need for enhanced science education. Continuing the tradition, along with training graduate students and postdoctoral researchers, undergraduates and high-school students extensively participate in this research. It will enormously benefit these younger generation by getting trained for future spin based nano technology.Technical:In this NSF supported individual project a series of investigations are proposed that focus on fundamental properties as well as applied aspects of magnetism, which will benefit both at the basic level as well as for the future spin-based information technology. Spin-polarized transport studies of several novel systems will be done to understand and manipulate the spin polarization (P), necessary for future spin devices. The role of the ferromagnet-insulator interface bonding is crucial in controlling the magnitude of P. Our aim is to control this bonding and explore novel tunnel barriers to achieve higher P, including the exploration of the Co-HfO2 system, predicted to have P=100%. Spin filter tunneling is one of the few ways in which near 100% P (demonstrated in our group in the past), which will be explored for achieving P=100% above LHe temperatures. Based on the electronic structures of the constituent CoB and FeB alloys, we believe it is possible to "tailor" the (Co,Fe)-B band hybridization to achieve even higher P and tunnel magnetoresistance (TMR) values. This material system remains largely unexplored and should open the way for candidate materials with high P, without the interface problems of a half metal ferromagnet. Exploiting dimensionality on a nanoscale, in particular, spin-polarized transport through quantum islands can give rise to novel effects such as spin-resonant tunneling, which can greatly enhance the TMR, as has been observed in our laboratory. Double magnetic tunnel junctions exploiting non-equilibrium spin accumulation and ballistic spin transport will be explored, with potential for novel devices such as spin transistors. As in the past in addition to graduate students, postdoctoral researchers and visiting scientists, undergraduates and high-school students participate in this research program. The education of students in science through this outreach program will continue in an effective way to meet the national need for science education.