MgO基Heusler合金隧道异质结的掺杂调控和自旋依赖热电输运

Due to a high Curie temperature and spin polarization, Heusler alloys are a the most promising half-metallic ferromagnet for applications in magnetic tunnel junctions. The Heusler magnetic tunnel junction with MgO tunneling layer is also the most possible material for high-promising electronic and thermal transition because of well-matched crystal structures. However, a significant reduction of tunnel magnetoresistance ratio against temperature was found in experimental investigations, which blocks development and application of MgO-based Heusler magnetic tunnel junction. As a prospective approach, the doping may be used to stabilize half-metallicity in Heusler alloys and mediate mechanical, physical and chemical properties in the Heusler herterojunctions for achieving excellent magnetic tunnel junctions. As a result, in this project, from the ab initio calculations we shall study the influences of doping, defect, disorder on the electronic structure, magnetism and polarizated electronic or thermal trasition in MgO-based Heusler alloy tunneling heterostructures, and explore spin-polarized transport properties of the magnetic tunning junctions and the mechanism of current-induced spin-transfer toques acting on the magnetic moments in the magnetic tunning junctions performed by Heusler alloys. This project is though to be a significant reseach for revealing deeply the thermal and electronic spin-polarized transportanion mechanism and current-induced magnetization dynamics without enormous cost.

Heusler合金具有较高的自旋极化和居里温度，是最具潜力应用于隧道结的半金属铁磁材料。以MgO为隧道层的Heusler合金隧道结，更是由于良好的晶格匹配而最可能实现高效的电、热输运。但是，实验中检测到MgO基Heusler合金隧道磁电阻具有严重的高温降落，限制了其进一步的应用开发。掺杂，作为极有希望的解决方案，可用来稳定合金的半金属性，调制隧道异质结界面的力学、物理和化学性质，设计出优良的隧道结。因此，本项目通过可信赖的从头计算方法，研究掺杂、缺隙、无序对MgO基Heusler合金隧道异质界面电子结构、磁性和电、热极化输运的影响，探索极化电流与磁化之间相互作用而引起的自旋波激发或电流感应磁化翻转的机制，以期在较少投入的情况下实现Heusler合金隧道结材料改性上的技术突破。本项目对设计磁遂道结器件有重要指导作用，也有助于发展自旋极化热、电输运和电流驱动的磁化动力学理论。

本项目为弄清楚MgO基Heusler合金隧道结的温度依赖因素和设计优质的隧道结材料，基于密度泛函理论的第一性原理计算，从Heusler合金的块体研究开始，广泛地寻找具有半金属行性的CuMnSb型half-Heusler合金，Cu2MnAl型Full-Heusler合金、Hg2CuTi型Inverse-Heusler合金、四元等比型Heusler合金，以及四元自旋无隙半导体型Heusler合金，并利用合适sp元素掺杂实现了这些合金半金属性的稳定。在此基础上，进一步考虑Heusler合金的表面热动力学稳定性、原子无序效应、电子结构及其自旋极化行为，率先论证掺杂表面半金属性存在的可能性。最后，重点研究MgO基Heusler合金的异质界面，系统考虑了这些界面上的原子相互作用、电子结构、磁性、掺杂无序和自旋极化效应等，揭示MgO基Heusler合金隧道结异质结设计的力学、磁性、自旋依赖电子输运等微观机制，为后续的实验研究和器件开发提供理论依据。