高性能有序钙钛矿磁性半金属新材料的高压制备与物性研究

In spintronic device, the spin degree of freedom of electron is used for signal transmission, processing, and storage. This type of device has a wide variety of potential applications because of the peculiar advantages in high density of storage, low energy consumption, and fast response. Since the electrical carrier is completely spin polarized, the magnetic half metal provides a desirable candidate to realize spintronic device. As a result, half metal has received much attention in the past decades. For practical applications of half metal, high spin ordering temperature (above room temperature), wide half-metallic energy gap, and large magnetic anisotropy energy are required to emerge. Unfortunately, however, in the half-metal materials discovered as yet, these three merits are very difficult to occur simultaneously. In this project, we will break the conventional synthesis conditions under ambient pressure and apply special high-pressure and high-temperature techniques to prepare magnetic half metals with A-site ordered AA'3B4O12 perovskite structure as well as both A- and B-site ordered AA'3B2B'2O12 perovskite structure. In these ordered perovskites, multiple atomic positions (A', B and B' sites) accommodate transition metals. Consequently, in addition to the usual B-site interaction, there also exist strong A'-site interaction and A'-B/B' intersite interaction. By appropriate magnetic ionic combination in these magnetic ionic sites, it is possible to sharply enhance the spin ordering temperature and tune the half-metallic gap as well as the magnetic anisotropy energy. Therefore, high-performance magnetic half metals are highly possible to form in these ordered perovskite systems, opening up a way to make advanced multifunctional spintronic devices in the future.

自旋电子器件基于电子自旋进行信息传递、处理与存储，具有存储密度高、能耗低、响应快等优点，在多个领域具有重要潜在应用。磁性半金属可提供完全自旋极化的载流子，被视为构建自旋电子器件的理想材料而备受关注。实际应用要求半金属材料具有室温以上的磁有序温度、较宽的半金属能隙以及显著的磁各向异性能。然而，目前已知的半金属材料很难同时满足上述要求。本项目将突破常规制备条件，利用独特的高压高温技术合成A位有序钙钛矿AA'3B4O12以及A、B位同时有序钙钛矿AA'3B2B'2O12等磁性半金属。这些体系多个原子位置(A'、B、B'位)容纳过渡金属离子，除了常见的B位相会作用外，也存在很强的A'位以及A-B/B'位间的相互作用。因此通过合适的磁性离子组合，一方面可大大提高(亚)铁磁有序温度，且可同时调控半金属能隙与磁各向异性能，从而形成综合性能优越的磁性半金属，为未来先进多功能自旋电子器件的应用提供材料基础。

自旋电子器件基于电子自旋进行信息传递、处理与存储，相比于传统半导体电子器件，具有存储密度高、能耗低、响应快等优点，在众多领域具有重要潜在应用。磁性（包括铁磁与亚铁磁）半金属一个自旋方向参与导电，另一个自旋方向打开能隙，理论上传导电子具有完全的自旋极化率，是自旋电子学的重要候选材料。如何寻找室温以上且具有较大能隙的高性能磁性半金属是当前的重要任务。本项目发挥高压高温在新材料制备方面的独特优势，通过把简单钙钛矿扩展至A、B位同时有序钙钛矿，调控A、B位不同的离子组合和价态组合方式，一方面加强总的磁相互作用强度以提高磁相变温度，另一方面改变外层电子分布增大半金属能隙，从而获得了亚铁磁居里温度在室温以上且半金属能隙高达1.6 eV的高性能半金属材料。由于大的半金属能隙会大大抑制禁带热激发可能产生的额外载流子，从而可确保在较高温度下导电载流子实现接近100%的自旋有序。因此，本项目发现的新型半金属为面向应用的自旋电子学器件提供了材料基础。在本项目的部分资助下，团队成员已发表学术论文28 篇，其中申请人作为通讯作者的论文26篇，包括Nat. Commun. 1篇、J. Am. Chem. Soc. 1篇、Nano Lett. 1篇、NPG Asia Mater. 2篇、Chem. Mater.+ Inorg. Chem. 7篇、Phys. Rev. B+Appl. Phys. Lett. 9篇，6篇被被NPG Asia Mater.、 Chem. Mater.等选为封面或亮点推荐论文、1 篇入选中国精品科技期刊顶尖学术论文（F5000）。此外，在新材料制备方面已授权发明专利4项，受邀学术会议报告6个，培养博士毕业生7名，其中1名荣获北京市/中科院优秀博士毕业生，且获得国家博士后创新人才计划资助。总之，本项目圆满完成了项目既定的各项目标和任务。