Growth and characterisation of frustrated kagome ferromagnet thin films

层状Kagome铁磁体Fe3Sn2具有巨大的狄拉克费米子和在室温下显示Skyrmions的受挫磁性。磁性Skyrmions很小(大小从nm到100s纳米)，稳定(受其非平凡的拓扑结构保护)，并且很容易移动(它们在低电流密度下对自旋力矩做出反应)。因此，它们是在新形式的自旋电子数据存储和逻辑器件中表示数据的有吸引力的候选者，这些数据存储和逻辑器件将是非易失性的，消耗的能量很少，并且允许适用于布尔计算和神经形态计算的新颖的内存中计算体系结构。到目前为止，人们只对Fe3Sn2进行了块状研究，但自旋电子器件需要薄膜。最近研究表明，相关化合物FeSnO_3可以在(111)SrTiO_3衬底上外延生长。由于两种化合物具有相同的Fe的Kagome位置和非常接近的晶格常数，我们预计我们可以在SrTiO_3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，并研究其电子输运和磁性，特别是与Skyrmions相关的性质。该项目的一个特点是，我们可以在氧化物异质结构的表面外延生长磁性金属层，每个氧化物异质结构都生长在生长系统的专用腔体中，并在超高电压下转移。这将确保堆叠中关键界面的最高质量的生长，我们将使用横截面样品的高分辨率透射电子显微镜来证实这一点。外延氧化物生长意味着还可能在异质结构中包括其他氧化物材料，如水溶性的Sr3Al2O6，它可以用来形成牺牲层，使薄膜能够漂浮起来，通过传输实验进行研究。除了为本项目中的透射电子显微镜表征提供平面图样本外，这些样本还将通过我们的合作者网络(如格拉斯哥大学和保罗·谢勒研究所)，通过洛伦茨或软X射线显微镜进行磁性成像。将奇异的电子结构和自旋织构与非平凡的实空间拓扑结构相结合，有望为研究由Berry相控制的磁输运现象带来新的见解，如拓扑霍尔效应。施加栅极电压将允许我们探测狄拉克点下方、上方和上方的传输。同时，天米子通过受挫而稳定的事实，而不是手性Dzyaloshinskii-Moriya相互作用的更常见的方法，意味着天米子的手性在原则上是可切换的，为数字数据的表示提供了一个双稳态变量。

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.