The role of defects in the magneto-ionic control of exchange-bias thin films

交换偏置是现代薄膜磁性中一个重要的界面效应。它为控制磁存储器、传感器、自旋电子学和磁电泳器件中铁磁层的残余磁化方向提供了一种优雅的方法。特别是，通过光离子轰击控制缺陷和能量的引入，可以在面内交换偏置薄膜中产生具有定制杂散场景观的人工磁畴图案。因此，光离子轰击提供了一种通用的方法来修改磁各向异性，但是，由于在连续轰击步骤中积累缺陷的影响，该技术无法实现对各向异性的可逆修改。通过电化学方法（磁离子控制）在磁性层中插入和去除离子对界面相关磁性能的可逆电控制是一个新兴的概念。然而，动力学受到材料中离子传输的限制。尽管缺陷被认为是离子传输路径的关键，但缺陷对磁离子开关的影响尚未得到系统的研究。在提出的项目中，缺陷修饰的交换偏置薄膜和磁离子界面控制的结合将作为一种新的方法来研究(i)交换偏置系统中人工磁畴的可逆编程和（ii）提高磁离子开关的速度和效率。对缺陷在磁离子开关中的作用的基本理解将为一般功能界面的调整开辟新的途径。例如，获得的知识也将为其他与界面相关的磁现象（如dzyaloshinskii - moriya相互作用或自旋轨道扭矩）的新设计选择铺平道路。

The exchange bias is an important interface-related effect in modern thin-film magnetism. It offers an elegant way to control the remnant magnetization direction of ferromagnetic layers in magnetic memories, sensors, spintronics and magnetophoretic devices. Especially, artificial magnetic domain patterns with tailored stray field landscapes can be created in in-plane exchange bias films by the controlled introduction of defects and energy via light-ion bombardment.Thus, light ion bombardment presents a versatile method to modify magnetic anisotropies, but, due to the influence of accumulating defects in successive bombardment steps a reversible modification of anisotropies cannot be achieved by this technology. The reversible electric control of interface-related magnetic properties by the insertion and removal of ions in magnetic layers via an electrochemical approach (magneto-ionic control) is an emerging concept. However, kinetics are limited by the ion transport in the material. Even though defects are expected to play a pivotal beneficial role as ion transport paths, the impact of defects on the magneto-ionic switching has not been studied systematically yet. In the proposed project, the combination of defect-modified exchange bias films and magneto-ionic interface control will be studied as a novel approach towards (i) a reversible programming of artificial magnetic domains in exchange bias systems and (ii) an increase in the switching speed and efficiency of magneto-ionic switching. The fundamental understanding of the role of defects for magneto-ionic switching will open up new avenues toward the tuning of functional interfaces in general. For instance, the gained knowledge will also pave a way to new design options for other interface-related magnetic phenomena such as the Dzyaloshinskii–Moriya-interaction or spin orbit torques.