RUI: Collaborative Research: Spin-gapless semiconductivity and half-metallicity in Heusler alloys

摘要：当前的计算技术是以操纵电子的电荷为目的进行信息处理。用于大规模存储数据的硬盘是利用电子的固有磁性来工作的。自旋电子学是一个新兴的领域，它将这两种技术结合在一起，创造了一种新的计算范式，可以大大提高计算速度和随之而来的能源效率。自旋电子器件，如磁性随机存取存储器（MRAM）已经商业化，但自旋电子学的潜力要大得多。该项目通过系统地发现具有必要的电子和磁性质的新材料来推动自旋电子学领域的发展，从而为大规模开发新的自旋电子器件奠定基础。该项目结合了理论和实验方法，以最大限度地提高发现过程的有效性。除了其直接的科学影响外，该项目还通过本科生在研究的各个方面的大量参与，对未来科技劳动力的发展产生积极影响。通过强调和提升科学对人类福祉的重要性的活动，涉及K-12学生和普通公众的外展计划进一步扩大了项目的影响。该项目由材料研究部（DMR）和促进竞争研究的既定计划（EPSCoR）共同资助。技术摘要：本项目的主要目标是鉴定和合成用于自旋电子学的新型半金属（HM）和无自旋间隙半导体（SGS）材料。该项目特别研究了HM和SGS Heusler合金的结构、磁性、电子和自旋输运特性。这是通过对候选材料进行全面的理论和实验研究来实现的，使用最先进的技术、工具和研究方法，包括x射线衍射、透射电子显微镜、量子设计VersaLab磁力计、量子设计物理特性测量系统、点接触安德烈夫反射和第一性原理密度泛函计算。该项目的动机是最近的发现，某些Heusler化合物在改变其元素组成后，其基态从金属变为SGS和/或HM。这种方法比文献中报道的机械应变诱导的半金属转变有明显的优势，因为它不需要外部压力。其次，该项目提供了实验证实，某些半金属在薄膜几何结构中保持100%的自旋极化，这与传统观点相反，即由于表面状态的出现，减少几何结构会破坏半金属性。这将为自旋电子应用打开新的一页，例如，基于多层设计的器件，如磁阻隧道结。该项目由材料研究部（DMR）和促进竞争研究的既定计划（EPSCoR）共同资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical Abstract:Current computing technology is based on the manipulation of the charge of electrons for the purpose of information processing. Hard disks, which are used in large-scale storage of data, function by exploiting the intrinsic magnetism of electrons. Spintronics is a fledging field that unites these two technologies to create a new computing paradigm that could result in substantial enhancements in computing speed and attendant energy efficiency. Spintronic devices such as magnetic random access memory (MRAM) have already been commercialized but the potential of spintronics is far greater. This project advances the field of spintronics through the systematic discovery of new materials that possess the necessary electronic and magnetic properties to undergird large-scale development of new spintronic devices. The project combines both theoretical and experimental approaches to maximize the effectiveness of the discovery process. In addition to its direct scientific impact, the project positively influences the development of the future science and technology workforce through the heavy involvement of undergraduate students in all aspects of the research. Outreach programs involving K-12 students and the general public further broadens the impact of the project via engaging activities that emphasize and elevate the importance of science to the well-being of humanity. This project is jointly funded by the Division of Materials Research (DMR) and the Established Program to Stimulate Competitive Research (EPSCoR).Technical Abstract:The main goal of this project is the identification and synthesis of new half-metallic (HM) and spin-gapless semiconducting (SGS) materials for applications in spintronics. In particular, this project investigates structural, magnetic, electronic, and spin-transport properties of HM and SGS Heusler alloys in bulk and thin-film geometry. This is achieved by performing comprehensive theoretical and experimental investigations of candidate materials, using state-of-the-art techniques, tools, and research methods, including X-ray diffraction, transmission electron microscopy, Quantum Design VersaLab magnetometer, Quantum Design Physical Property Measurement System, point-contact Andreev reflection, and first-principles density functional calculations. The project is motivated by recent discovery that certain Heusler compounds change their ground state from metallic to SGS and/or HM upon modification of their elemental compositions. This approach has a clear advantage over mechanical strain-induced half-metallic transitions reported in the literature, as it requires no external pressure. Second, this project provides experimental confirmation that certain half-metals retain a 100% spin-polarization in thin-film geometry, contrary to the conventional wisdom that reduced geometry destroys half-metallicity due to the emergence of surface states. This could open a new page in spintronic applications, e.g., in devices based on multilayer design, such as magnetoresistive tunnel junctions. This project is jointly funded by the Division of Materials Research (DMR) and the Established Program to Stimulate Competitive Research (EPSCoR).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.