垂直磁各向异性钴铁基磁性薄膜的制备及其在自旋转矩振荡器中的应用

The exploration of high performance perpendicular magnetic anisotropy (PMA) materials is one of the most important driving forces in the development of ultra-high density magnetic memory materials, permanent magnet materials and spintronic devices. According to the theoretical calculations and the experimental results, the cobalt-iron based magnetic thin films with special structure and compositions, specifically lattice distorted cobalt-iron film, half-metallic Co2FeAl film, possess large PMA energy and high saturation magnetization. Such unique features lead to a broad research and application prospect. Based on our previous works, we plan to prepare the CoFe-based thin films with large PMA, by means of high-vacuum magnetron sputtering technology. The effects of sputtering conditions, substrates, buffer layer, film composition, thickness and other factors on the lattice structure, static and dynamic magnetic properties of CoFe-based films will be investigated. We will explore the correlation mechanisms between the magnetic properties and the preparation parameters and obtain the optimal preparation conditions. On the other hand, the PMA CoFe-based films can be applied to the free layer of spin-torque oscillators (STOs). By systematic changing the composition and thickness of free layer, capping layer, the effects of PMA on the output characteristics of STOs will be investigated. The physical mechanisms of spin transport, spin torque and magnetic moment precession will be clarified. Finally, by optimizing the microstructures of STOs, the STOs with large emission power and high Q-factor are obtained, and the practical application process of spin torque oscillators will be accelerated.

高性能垂直磁各向异性材料的研发，是制备超高密度磁存储材料、永磁材料、自旋电子器件最重要的推动力之一。理论计算和实验表明，某些特殊结构、成分的钴铁基磁性薄膜，具体为晶格形变CoFe膜、半金属Co2FeAl膜，呈现优异的垂直磁各向异性和高饱和磁化强度，具有广阔的研究和应用前景。本研究拟在前期工作基础上，运用高真空磁控溅射手段，制备具有高垂直磁各向异性的钴铁基薄膜，系统研究溅射条件、基片、薄膜成分、厚度、缓冲层等因素，对薄膜的晶体结构、静态、高频动态磁性能的影响，探索薄膜磁性能与各调控参数之间的关联机制，得到最优制备工艺。同时，将钴铁基薄膜应用于自旋转矩振荡器（STO）的自由层中，系统性的调控自由层薄膜成分、厚度、盖帽层等条件，研究垂直磁各向异性能大小对STO微波输出特性的影响，阐明自旋输运、自旋转矩、磁矩进动等物理机理；通过优化振荡器的微结构，制备高功率、高品质因数的STO，加快其实用化进程。

高性能垂直磁各向异性材料的研发，是制备超高密度磁存储材料、永磁材料、自旋电子器件最重要的推动力之一。通过本项目的支持，申请人以FeCo基材料为研究体系，系统研究了多种因素对薄膜晶格和磁各向异性能的影响，利用磁控溅射方法成功制备出多种具有高垂直磁各向异性的FeCo基薄膜材料，包括[FeCo/Pt]n多层膜，[FeCo/Ir]n多层膜，FeCo/FePt双层膜，以及FeCo/CoPt双层膜。这种同时具备高垂直磁各向异性和高饱和磁化强度的磁性薄膜具有广阔的研究和应用前景。同时，利用微磁学模拟软件OOMMF模拟研究了电流密度、磁各向异性能、器件大小对自旋转矩振荡器性能影响，为后续实验做指导。在此基础上，将高垂直磁各向异性的FeB基薄膜应用于自旋转矩振荡器的自由层制备当中，通过优化自旋转矩振荡器的结构、形貌，成功制备出高输出功率（大于2.5 μW）、高品质因数（大于5000）的自旋转矩振荡器。为自旋转矩振荡器的实用化提供实验依据。此外，通过化学方法合成了多种金属磁性纳米颗粒，例如CoFex@Co、Fe3O4、FeS2、Ni磁性颗粒，制备了磁性纳米颗粒/导电介质复合材料，系统研究了材料的结构、形貌和高频电磁性能，成功制备出多种性能优异的高频电磁材料。