CoFe基磁性金属薄膜中热自旋流的高效生成及机理研究

The discovery of the new physical effect on thermally excited spin current has greatly promoted the research of interaction between spin and heat currents and developed into one new branch of Spintronics, nominated as Spin Caloritronics. The utilization of thermal spin current enables us to simplify device integration and develop wireless spintronic devices. However, the extremely low generation efficiency of thermal spin current limits its application in conventional ferromagnetic materials. We recently found the CoFeAl nanostructure show excellent thermal spin injection efficiency, but it still not enough for the practical application. Besides, its basic physical mechanism is still not well understood. In this project, we will focus on the efficient thermal spin current generation and injection in the CoFe based ferromagnetic thin films and its multi-layered structures. Firstly, we will optimize the thermally excited spin generation efficiency by adjusting composition of CoFeX ferromagnetic layer with improving interface condition in fabricated CoFeX/Cu/Pt structure. And then, we will study the influence of thermally excited spin generation with saturation of magnetization, Curie temperature, spin-dependent Seebeck coefficient and interfacial condition. Moreover, we will establish the intrinsic relationship between the magnon energy, spin density of states around Fermi level with efficient thermal spin injection in ferromagnetic thin films. Finally, we will reveal the origin mechanism of thermally excited spin generation and injection in CoFe based metallic junctions for promoting the development of efficient energy harvesting devices, multi-functional sensors with low power consumption and spin information storage devices.

热激发生成自旋流的发现大大推进了热流与自旋流之间转换的研究并成为自旋电子学的新兴学科，即自旋热学。利用热自旋流不但可开发无线自旋器件还可大大简化电路集成。我们最近研究发现CoFeAl具有较高的热自旋转换效率，但还难以满足应用需求，且其高效生成热自旋流的基本物理机制还不完全清楚。因此本项目拟以CoFe基磁性金属及其多层异质结为研究对象，通过测量逆自旋霍尔效应研究成分调控及界面改性提高CoFe基磁性薄膜及其三层异质结中热自旋流生成和注入效率；并分析由成分调控引起饱和磁化强度、居里温度、自旋依赖的赛贝克系数以及界面对热自旋流生成和注入的影响；建立热自旋流生成和注入与磁性金属中磁振子的能量、自旋电子在费米能级附近态密度以及界面自旋混合电导的内在联系；揭示磁性金属薄膜中高效热自旋流生成和注入的基本物理机制，为开发高效纳米结构能量收集器件、微型化低能耗新型多功能传感器以及自旋信息存储器提供新的思路。

热激发生成自旋流的发现大大推进了热流与自旋流之间转换的研究并成为自旋电子学的新兴学科，即自旋热学。利用热自旋流不但可开发无线自旋器件还可大大简化电路集成。本项目针对磁性金属薄膜及异质结中高效热自旋流生成和注入的基本物理机制和热自旋注入效率进行了系统研究，开发了热自旋注入效率的精确探测方法，揭示了异质结界面磁有序是高效热自旋注入效率调控机制，并利用高效自旋热电转换异质结开发出新型热电转换器件。首先研究了CoFeAl/Cu/Py横向自旋阀中电流产生的电流和热流激发生成自旋流的影响，通过对电流激发热非局域自旋信号不满足电流和电压的电极对易关系的分析，开发了自旋依赖塞贝克系数精确测量的简易方法。而后运用该横向自旋阀结构中非对易性测试方法探究铁磁材料Py(Ni80Fe20)/Cu异质结中热激发自旋电流特性的温度相关性，发现Py/Cu界面的自旋相关的塞贝克系数在低温下明显增加，且在较低温度下热自旋极化超过了100%。通过第一性原理计算Py/Cu界面能带结构发现自旋塞贝克系数对界面处的磁无序散射十分敏感，界面磁无序度的减小可以显著增大热自旋注入效率，揭示了常用金属异质结中界面对热自选转化的调节机制。还研究了纵向异质结构及热电器件的制备和开发，结合高效热电转化异质结及界面调控机制开发具有较大输出功率、可以用微型低能耗、自供电的新型热电转换器件。这些研究使得高效热自旋能量转换从理论到应用跨出了一步。