Studies of Spin-Electronic Materials Using Synchrotron Radiation

这项提案是为了响应21世纪的自旋电子学倡议，计划征集NSF 02-036而收到的。该提案的重点是使用同步辐射对自旋电子材料进行X射线研究。利用最先进的同步辐射技术，包括扩展X射线吸收精细结构(EXAFS)、近边X射线吸收精细结构(NEXAFS)和X射线磁性圆二色谱(XMCD)，系统地研究了磁性半导体中组成原子周围的短程有序结构、化学价和局域磁矩。此外，还将利用掠入射X射线散射(GIXS)和X射线荧光角度依赖(ADXRF)技术研究磁性离子在各种自旋注入器件中的界面形态、成分混合和扩散深度分布。从这些X射线实验中获得的纳米结构信息对于理解创新的自旋电子材料用于器件应用的特殊电子和磁性的机制是重要的。被研究的材料包括数字合金和III-V磁性半导体的随机合金，其中一些已经被发现居里温度高于室温。其他磁性化合物半导体，如II-VI，II-IV-V2，和II-VI2系统的室温铁磁性也将被研究。这些实验方法是基于该研究团队在过去十年中使用X射线散射、荧光和吸收技术对III-V磁性合金半导体和异质结构进行无损表征的丰富经验。该小组利用线偏振和圆偏振的软X射线和硬X射线进行材料研究。没有多少其他X射线研究团队在两种偏振类型的两种波长范围内进行实验。在这些实验中获得的纳米结构信息将被用作对晶体/外延层生长者的反馈，用于对材料进行无损评估，并从中选择更合适的条件来改进材料特性以满足器件要求。在即将到来的2002-2004财政年度，这项研究计划将重点放在以下方面：(I)磁性合金半导体和磁性数字合金中磁性离子周围的局域结构，以及(Ii)磁性半导体和金属/合金异质结中磁性离子的界面形态、成分混合和扩散深度分布及其与自旋注入效率的关系。这项研究有望对层状磁性半导体的基本理解和新型磁性材料在自旋电子激发领域的应用做出重要贡献。

This proposal was received in response to the Spin Electronics for the 21st century Initiative, Program Solicitation NSF 02-036. The proposal focuses on x-ray studies of spin-electronic materials using synchrotron radiation. Systematic investigation of short-range-order structure, chemical valency, and local magnetic moment around constituent atoms in magnetic semiconductors will be carried out using state-of-the-art synchrotron radiation techniques including extended x-ray absorption fine structure (EXAFS), near-edge x-ray absorption fine structure (NEXAFS) and x-ray magnetic circular dichroism (XMCD). In addition, interface morphology, compositional intermixing and diffusion depth profile of magnetic ions in various heterostructures used in spin-injection devices will also be investigated by grazing incidence x-ray scattering (GIXS) and angular dependence of x-ray fluorescence (ADXRF) techniques. The nanostructure information obtained from these x-ray experiments is important for understanding the mechanisms responsible for the special electronic and magnetic properties of innovative spin-electronic materials for device applications. The materials to be studied include digital alloys and random alloys of III-V magnetic semiconductors, some have already been found with a Curie temperature above the room temperature. Other magnetic compound semiconductors such as II-VI, II-IV-V2, and II-VI2 systems with room-temperature ferromagnetism will also be investigated. These experimental approaches are based on this research team's extensive experience in the past decade of using x-ray scattering, fluorescence, and absorption techniques for nondestructive characterization of III-V magnetic alloy semiconductors and heterostructures. This group makes use of both soft and hard x-rays with both linear and circular polarization for materials research. Not many other x-ray research teams are doing experiments in both wavelength regimes with both types of polarization. The nanostructure information obtained in these experiments will be used as a feedback to crystal/epilayer growers for nondestructive evaluation of the materials, and from which to select more appropriate conditions for improving the material characteristics to meet device requirements. For the upcoming fiscal years 2002-2004, this research program will emphasize on the following areas: (i) local structures around magnetic ions in magnetic alloy semiconductors and magnetic digital alloys, and (ii) interface morphology, compositional intermixing and diffusion depth profile of magnetic ions in heterostructures of magnetic semiconductors and metals/alloys as well as their relation with spin-injection efficiency. The proposed research is expected to make significant contributions to both fundamental understanding of layered magnetic semiconductors and applications of the new magnetic materials in the exciting field of spin-electronics.