垂直磁各向异性CoFeB-MgO相关薄膜结构的阻尼调控

Attributed to the hybridization of Fe-3d and O-2p orbitals at CoFeB-MgO interfaces, the perpendicular magnetic anisotropy has promoted the researches on the related thin film structures, such as magnetic-tunnel-junctions. The main challenge facing their applications is the tuning of damping. However, in CoFeB-MgO related thin film structures, the origin and mechanism of damping are still unclear, the possible correlation between the intrinsic Gilbert damping and the perpendicular magnetic anisotropy has not been clarified, and the effective tuning method of damping is lacking. Therefore, in this project, aiming at the reducing of intrinsic Gilbert damping, we propose to disclose the origin, mechanism and contribution of damping through the investigation and analyzing of its dependences on magnetic field, frequency, angle, temperature and the structure aspects of thin film structures. The influences of CoFeB layer and the interfaces of both CoFeB-MgO and CoFeB-Ta on damping and perpendicular magnetic anisotropy will be studied. The intrinsic Gilbert damping is going to be reduced by tuning the composition, inserting layers at interfaces, and optimizing the annealing process. Based on these studies, we will clarify the possible correlation between the intrinsic Gilbert damping and the perpendicular magnetic anisotropy. This project will contribute to the applications of these CoFeB-MgO related thin film structures with perpendicular magnetic anisotropy in spintronic units and devices.

CoFeB-MgO界面Fe-3d和O-2p轨道杂化产生的垂直磁各向异性，推动了磁隧道结等相关薄膜结构的研究，其应用的主要挑战在于阻尼调控。然而，CoFeB-MgO相关薄膜结构中，阻尼来源机制还不明确，本征Gilbert阻尼与垂直磁各向异性可能存在的关联尚未厘清，缺乏有效的阻尼调控手段。对此，本项目以降低本征Gilbert阻尼为目标，通过磁场、频率、角度、温度以及薄膜结构参数等调制阻尼，分析其变化规律，揭示阻尼的来源机制与贡献；研究CoFeB层及CoFeB-MgO、CoFeB-Ta界面的微观状态对阻尼及垂直磁各向异性的影响规律，通过成分调控、界面插层、热处理优化等方式降低本征Gilbert阻尼；在此基础上，厘清本征Gilbert阻尼和垂直磁各向异性之间的关联。本项目对垂直磁各向异性CoFeB-MgO相关薄膜结构在自旋电子学单元和器件中的应用具有重要意义。

本项目以磁隧道结等自旋电子学单元与器件应用为背景，针对其存在的缺乏有效阻尼调控手段和与磁各向异性之间的关联尚未厘清等问题，围绕CoFeB-MgO等薄膜界面垂直磁各向异性、阻尼特性、自旋波激发、自旋霍尔效应等，开展了系统研究，取得如下结果：.在MgO/CoFeB/Ta薄膜中，研究了薄膜厚度对垂直磁各向异性和“死层”的影响规律，实现了显著的垂直磁各向异性，分析了阻尼机制和贡献，在垂直方向得到0.016的较低本征Gilbert阻尼值。利用稀土基强自旋耦合材料Cu1-xTbx对CoFeB自旋霍尔效应进行了有效调制，发现随着Tb含量的增加，显著的自旋泵浦效应带来更大的有效磁阻尼，自旋散射从斜散射机制转为边跳机制，自旋霍尔角增大，自旋扩散长度因Tb的散射而减小。在CoFeMnSi薄膜中得到0.0019的超低阻尼值，验证了其自旋零能隙半导体特征。.利用柔性衬底在(FeCo/IrMn)3/Ta多层薄膜沉积过程中施加应变，将交换偏置场从20 Oe提高到200 Oe，铁磁共振分析将其归因于应变导致的双重磁各向异性之间非共线角度的变化。在Co2FeSi薄膜中引入非均匀分布的磁各向异性场，利用超快激光激发出包括偶极和交换模式在内的多种自旋波模式，同时影响了自旋轨道耦合作用，实现了阻尼因子大幅度可调。.此外，基于四元等比Heusler合金中新型自旋零能隙半导体的设计，实现了费米能级附近的高线性色散关系，极大提升了电子的迁移率。在MnMX六角合金中实现了自旋重取向和磁晶各向异性的同步调控，获得了极低临界磁场的双拓扑型磁斯格明子，通过粉末中子衍射确定了其非共线的倾角磁结构，建立了微观磁结构与斯格明子磁畴的关联。通过三维连续转角，在二维层状铁磁性材料Fe3GeTe2中报道了磁场沿着面内的新奇拓扑霍尔效应，证实了其中可能存在的斯格明子拓扑磁畴。.综上，本项目围绕CoFeB-MgO等相关薄膜结构，开展了阻尼机制、磁各向异性及其有效的调控手段方面的研究，分析了实验规律，揭示了来源机制和相互关联，实现了低阻尼与高磁各向异性，对于自旋电子学单元的设计和器件应用具有重要意义。