Growth and characterisation of frustrated kagome ferromagnet thin films

层状铁磁体Fe3Sn2具有大量的狄拉克费米子和在室温下表现出的弱磁性。磁性粒子很小（纳米到100纳米大小），稳定（受其非平凡拓扑结构的保护）并且易于移动（它们在低电流密度下响应自旋力矩）。因此，它们是新形式的自旋电子数据存储和逻辑设备中数据表示的吸引人的候选者，这些设备将是非易失性的，消耗很少的能量，并允许适合布尔和神经形态计算的新型内存计算体系结构。到目前为止，Fe3Sn2只研究了大块形式，但自旋电子器件需要薄膜。最近的研究表明，相关化合物FeSn可以在（111）SrTiO3上生长为外延薄膜。由于这两种化合物具有相同的铁原子位置和非常接近的晶格常数，我们期望可以在SrTiO3上生长Fe3Sn2。在这个项目中，我们将开发在利兹最先进的罗伊斯研究所多室沉积系统中生长Fe3Sn2薄膜的方法，在布拉格中心使用世界领先的电子显微镜对薄膜进行表征，并研究它们的电子传输和磁性能，特别是与skyrmions相关的磁性能。这个项目的一个特点是我们可以在氧化物异质结构的表面外延生长磁性金属层，每个都在生长系统的专门腔室中生长，并在特高压下转移。这将确保堆叠中关键界面的最高质量生长，我们将使用高分辨率透射电镜的横截面样品来确认。外延氧化生长意味着也可以在异质结构中加入其他氧化材料，如水溶性的Sr3Al2O6，它们可以形成牺牲层，使薄膜可以通过透射实验飘出进行研究。除了在该项目中为TEM表征提供平面视图样品外，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。具有自旋织构的奇异电子结构与非平凡的实空间拓扑的结合有望导致对贝里相控制的磁输运现象的新见解，例如拓扑霍尔效应。施加栅极电压将允许我们探测狄拉克点以下、处和以上的输运。与此同时，skyrmions是通过受挫稳定的，而不是更常见的手性Dzyaloshinskii-Moriya相互作用，这一事实意味着skyrmions的手性原则上是可切换的，为数字数据的表示提供了一个双稳态状态变量。

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.