Growth and characterisation of frustrated kagome ferromagnet thin films

分层的可果美铁磁体Fe 3Sn 2具有大量的狄拉克费米子和在室温下显示skyrmions的受抑磁性。磁性skyrmions很小（nm到100 nm的大小），稳定（受其非平凡拓扑结构的保护）并且容易移动（它们在低电流密度下对自旋力矩做出响应）。因此，他们是有吸引力的候选人表示的数据在新形式的自旋电子数据存储和逻辑设备，将是非易失性的，消耗很少的能量，并允许新的计算存储器架构适合于布尔和神经形态计算。到目前为止，Fe 3Sn 2仅以块体形式进行研究，但自旋电子器件需要薄膜。最近已经表明，相关化合物FeSn可以作为外延薄膜在（111）SrTiO 3上生长。由于这两种化合物具有相同的kagome位置的Fe具有非常接近的晶格常数，我们期望我们可以在SrTiO 3上生长Fe 3Sn 2。在这个项目中，我们将开发的手段来生长薄膜的Fe 3Sn 2在国家的最先进的罗伊斯研究所多室沉积系统在利兹，使用世界领先的电子显微镜在布拉格中心的薄膜，并研究其电子传输和磁性，特别是那些与skyrmions。该项目的一个特殊特点是，我们可以在氧化物异质结构的表面上外延生长磁性金属层，每个层都在生长系统的专用腔室中生长，并在超高真空下转移。这将确保堆栈中关键界面的最高质量生长，我们将使用横截面样品的高分辨率TEM进行确认。外延氧化物生长意味着还可以在异质结构中包括其他氧化物材料，例如水溶性Sr 3Al 2 O 6，其可以用于形成牺牲层以允许薄膜浮起，用于通过透射实验进行研究。除了在本项目中提供TEM表征的平面图样品外，这些样品还将通过我们的合作者网络（例如，格拉斯哥大学和Paul Scherrer研究所），通过洛伦兹或软X射线显微镜进行磁成像。一个奇异的电子结构与自旋纹理与非平凡的实空间拓扑结构的结合，预计将导致新的见解磁输运现象所管辖的Berry相，如拓扑霍尔效应。施加栅极电压将使我们能够探测狄拉克点以下、狄拉克点处和狄拉克点以上的输运。与此同时，skyrmion是通过挫折稳定的，而不是更常见的手征Dzyaloshinskiiii-Moriya相互作用的手段，这意味着skyrmion手征性原则上是可切换的，为数字数据的表示提供了一个可转换的状态变量。

The layered kagome ferromagnet Fe3Sn2 has massive Dirac fermions and frustrated magnetism that shows skyrmions at room temperature. Magnetic skyrmions are small (nm to 100s of nm in size), stable (protected by their non-trivial topology) and easily moved (they respond to spin torques at low current densities). As such they are appealing candidates for the representation of data in new forms of spintronic data storage and logic devices that will be non-volatile, consume little energy, and permit novel compute-in-memory architectures suitable for both Boolean and neuromorphic computation. So far Fe3Sn2 has only been studied in bulk form, but thin films are required for spintronic devices. It has recently been shown that the related compound FeSn can be grown as an epitaxial thin film on (111) SrTiO3. Since both compounds have the same kagome places of Fe with a very close lattice constant, we expect that we could grow Fe3Sn2 on SrTiO3. In this project we will develop the means to grow thin films of Fe3Sn2 in the state-of-the-art Royce Institute multi-chamber deposition system at Leeds, characterise the films using world-leading electron microscopy in the Bragg Centre, and study their electron transport and magnetic properties, especially those related to skyrmions. A particular feature of this project is that we can grow the magnetic metal layer epitaxially on the surface of an oxide heterostructure, each grown in a specialised chamber of the growth system and transferred under UHV. This should ensure the highest quality growth of the critical interfaces in the stack, which we shall confirm using high resolution TEM of cross-section specimens. The epitaxial oxide growth means that it will also be possible to include other oxide materials in the heterostructure such as water-soluble Sr3Al2O6, which can be used to form a sacrificial layer to allow the thin film to be floated off for study by means of transmission experiments. As well as providing plan-view samples for TEM characterisation within this project, such samples will also be useful for magnetic imaging by means of Lorentz or soft x-ray microscopy through our network of collaborators, e.g. at the University of Glasgow and Paul Scherrer Institute. The combination of an exotic electronic structure with spin textures with non-trivial real-space topology is expected to lead to new insights into magnetotransport phenomena governed by the Berry phase, such as the topological Hall effect. Applying gate voltages will allow us to probe transport below, at, and above the Dirac point. Meanwhile, the fact that skyrmions are stabilised by frustration, rather than the more usual means of a chiral Dzyaloshinskii-Moriya interaction means that the skyrmion chirality is in principle switchable, providing a bistable state variable for the representation of digital data.