Functional layers of nanometer-thick YIG films and microstructured surfaces for spintronic applications

磁振子，也被称为磁振子自旋电子学，是一个迅速发展的自旋波物理学的新分支，专门研究自旋波及其量子磁子在信息传输和处理中的用途。为了实现这一目标，需要将电信号转换成磁振子电流，并在磁子芯片中进行处理，然后转换回电子形式。到目前为止，3D金属和合金(如坡莫合金)以及半金属(如Heusler化合物)已用于这些目的。然而，所有现有的磁性金属都具有相当高的磁阻尼，将自旋波的自由路径限制在微米范围内。相比之下，单晶Yttrium Iron Garnet(YIG)是一种磁绝缘体，其阻尼值要小两个数量级，允许自旋波在厘米距离内传播。此外，由于材料是电绝缘体，基于YIG的自旋电子片上器件承诺降低能源消耗，因为避免了与电子运动相关的寄生加热。尽管YIG薄膜的气相外延技术取得了巨大的进展，但到目前为止，只有微米厚的LPE薄膜才能获得固有的低阻尼值，这与亚微米级的磁子器件不兼容。但是，较小的厚度与较大的比表面积/体积膜比密切相关，这对于在YIG/金属双层中利用SHE和STT现象进行有效的电子-磁振子信号转换是至关重要的。因此，低阻尼纳米LPE薄膜的制备是近年来的研究热点，需要新的思路和概念。该项目的目标是开发、表征和微细加工超低损耗、超薄(20-100 nm)的YIG薄膜。与此同时，YIG/金属双层转换器所需的具有极其光滑和无缺陷表面的薄膜的制造将受到极大的关注。薄膜生长概念的开发、薄膜生长、亚微米磁性结构图案的初步实验以及生长技术的迅速优化将在Innovente.V.和TU Kaiserslautern的合作伙伴之间密切合作进行。Innovente.V.的研究人员是石榴石外延生长方面的杰出专家，而凯泽斯劳滕团队则以他们在磁石领域的基本贡献而闻名。在该项目的框架内，Innovente.V.的一项新的液相外延技术将与凯泽斯劳滕公司的现代微制造技术结合使用，以实现亚微米YIG结构。凯撒斯劳滕小组开发的布里渊光散射表征技术以及复杂的微波方法将用于测试YIG磁子器件。

Magnonics, also called magnon spintronics, is a rapidly growing new branch of spin-wave physics, specifically addressing the use of spin waves and their quanta, magnons, for information transport and processing. To realize this aim, electric signals need to be converted into magnon-currents and processed in a magnonic chip and converted back into electrical form. Up until now, 3d metals and alloys such as Permalloy, as well as half-metals such as Heusler compounds, have been used for these purposes. However, all existing magnetic metals have rather high magnetic damping, limiting the spin-wave free path to the micrometer range. By contrast, single crystalline Yttrium Iron Garnet (YIG) is a magnetic insulator with damping which is two orders of magnitude smaller, allowing for spin-wave propagation over centimeter distances. Moreover, since the material is an electrical insulator, YIG-based spintronic on-chip devices promise decreased energy consumption since parasitic heating associated with electron motion is avoided. Despite huge advances in the gas phase epitaxy of YIG thin films intrinsic low damping values could only be achieved for micrometer-thick LPE films to date which are not compatible with sub-micrometer magnonic devices. But a small thickness goes hand-in-hand with a large surface area to volume film ratio, which is of crucial importance for efficient electron to magnon signal conversion using SHE and STT phenomena in YIG/metal bi-layers. Therefore, growth of nanometer-thin LPE films with low damping is a recent topic of investigations and demands new ideas and concepts. The aim of the project is the development, characterization and microfabrication of ultra-low damping, ultra-thin (20-100 nm) YIG films. Simultaneously, strong attention will be focused on fabrication of films having extremely smooth and defect-free surfaces required for YIG/metal bi-layer converters. The development of a thin-film growth concept, film growth, and first experiments on the patterning of sub-micrometer magnonic structures as well as a prompt optimization of the growing technology will be carried out in close collaboration between the partners from Innovent e.V. and TU Kaiserslautern. The researchers from Innovent e.V. are distinguished experts in the epitaxial growth of garnets, while the Kaiserslautern group is known for their fundamental contributions to the field of magnonics. Within the framework of the project, a novel liquid phase epitaxy technology from Innovent e.V. will be used together with modern microfabrication techniques available in Kaiserslautern to realize sub-micrometer YIG structures. Brillouin light scattering characterization techniques developed by the Kaiserslautern group as well as sophisticated microwave methods will be used to test the YIG magnonic devices.