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

非技术：在基础研究的进步以及对超高密度磁存储不断增长的需求的推动下，最近人们对基于电子自旋传输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磁学的基本性质和应用方面，预计将在基础水平上对该领域以及未来基于自旋的信息技术产生影响。为了达到这一目标，将开展几个新系统的自旋极化输运研究，并了解和操纵自旋极化P(输运电子的自旋极化程度)，并开发“定制”材料。例如，我们将探索钴-铁-硼合金系统，它最近显示出非常大的隧道磁阻(TMR)值(越高越有应用价值)，以获得更高的P和TMR值。这种材料体系在很大程度上仍未被探索，这项研究应该会为P接近100%的候选材料开辟道路，而不会出现半金属铁磁体的界面问题。铁磁-绝缘体界面结合是控制P的大小的关键。我们的目标是控制这种结合以获得更高的P。使用量身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，自旋极化输运通过量子岛产生了新的效应，如自旋共振隧穿，这可以极大地提高TMR(在我们实验室观察到的)，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以有效的方式满足国家对加强科学教育的需求。延续这一传统，在培养研究生和博士后研究人员的同时，本科生和高中生广泛参与到这项研究中来。技术：在这个由美国国家科学基金会资助的个人项目中，我们提出了一系列的研究，集中在磁性的基本性质和应用方面，这将在基础水平和未来的基于自旋的信息技术方面都受益。将对几个新系统进行自旋极化输运研究，以了解和操纵自旋极化(P)，这是未来自旋装置所必需的。铁磁-绝缘体界面结合的作用对控制P的大小至关重要。我们的目标是控制这种结合并探索新的隧道势垒以获得更高的P，包括对Co-HfO2系统的探索，预计P=100%。自旋过滤隧穿是实现接近100%P的少数几种方法之一(我们的小组在过去证明了这一点)，这将被探索以实现高于LHe温度的P=100%。基于CoB和FeB合金组分的电子结构，我们认为有可能“定制”(Co，Fe)-B带杂化，以获得更高的P和隧道磁阻(TMR)值。这种材料体系在很大程度上仍未被探索，应该会为具有高P的候选材料开辟道路，而不会出现半金属铁磁体的界面问题。利用纳米尺度上的维度，特别是通过量子岛的自旋极化输运可以产生新的效应，如自旋共振隧穿，这可以大大增强TMR，正如我们实验室观察到的那样。将探索利用非平衡自旋积累和弹道自旋输运的双磁隧道结，并有可能开发出新的器件，如自旋晶体管。与以往一样，除了研究生、博士后研究人员和来访的科学家、本科生和高中生外，还参与了这一研究项目。通过这一推广计划对学生进行科学教育将继续以有效的方式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.