Voltage-tunable magnetic hysteresis and domain patterns by electrochemical reactions

在自旋电子学和磁流体芯片实验室系统领域中，对薄膜磁性的控制在许多现代器件方案中起着关键作用。外界电压对磁性的操控被认为是替代焦耳加热的基于电流的方法的一种节能方案。在磁性电压控制的研究领域中，纳米磁性的电化学(磁离子)控制是一个迅速兴起的课题。在利用磁性薄膜中的电化学相变时，外部电压对磁性状态的大效应和非易失性设置都是可以达到的。在所提出的项目中，我们想要研究可逆的电化学反应来调节金属/氧化物薄膜的磁滞和磁畴。我们打算使用铁基和钴基磁性薄膜作为电极和液体电解液，以增强磁场效应和提高磁体/电解液界面上的离子迁移率。将分析通过电化学转变产生的结构、成分和微观结构变化的作用，并将其与磁性变化相关联。我们希望找出磁离子反应的关键影响因素和提高反应层厚度和高度可逆性的条件。我们将努力获得一种具有非易失性的可调Fe或Co层，其中磁性状态可以通过中等电压和小初始电流来设置。这种可调的顶层与表现出垂直磁各向异性的底层的组合有望将磁离子效应的可变性指数化。理想情况下，可逆的磁离子自旋重定向将在几个纳米内实现。为了跟踪电解液在极化过程中的局部磁场变化，将开发一种与克尔显微镜兼容的电化学池。这种原位克尔显微镜装置有望首次解决使用液体电解液时磁离子反应对磁区的局部影响。对于电压可调的杂散场景观和磁壁陷阱，我们将研究图案化结构中的磁离子效应。

The control over magnetic properties in thin films plays a pivotal role in a multitude of modern device proposals in the fields of spintronics and magnet-based fluidic lab-on-chip systems. The manipulation of magnetism by an external voltage is strongly discussed as an energy-efficient alternative to current-based approaches that suffer from Joule heating. Within the research field of voltage control of magnetism, the electrochemical (magneto-ionic) control of nanoscale magnetism is a rapidly emerging topic. Both large effects and non-volatile setting of magnetic states by an external voltage come within reach when exploiting electrochemical phase transformations in magnetic films.In the proposed project we want to investigate reversible electrochemical reactions for voltage-tuning the magnetic hysteresis and domains of metal/oxide films. We intend to use Fe- and Co-based magnetic thin films as electrodes and liquid electrolytes that enable enhanced electric field effects and high ionic mobility at the magnet/electrolyte interface. The role of structural, compositional and microstructural variations occuring through electrochemical transformations will be analyzed and correlated with magnetic property changes. We expect to identify the key influencing factors and the conditions for enhanced reaction layer thickness and high reversibility of the magneto-ionic reactions. We will strive for a tunable Fe or Co layer with non-volatile behavior, where the magnetic state can be set by a moderate voltage and small initial current. The combination of such tunable top layers with bottom layers exhibiting perpendicular magnetic anisotropy promises to exponentiate the variability of magneto-ionic effects. Ideally, reversible magneto-ionic spin reorientation will be achieved within several nanometers.To track local magnetic changes during polarization within the electrolyte, an electrochemical cell compatible with Kerr microscopy will be developed. This in situ Kerr microscopy setup promises to resolve, for the first time, the local effect of magneto-ionic reactions on magnetic domains when using liquid electrolytes. Magneto-ionic effects in patterned structures will be investigated for voltage-tunable stray field landscapes and domain wall traps.