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

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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.