Spin current transport experiments on 3-dimensional Y3Fe5O12 surfaces utilizing atomic layer deposition

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Yttrium iron garnet (Y3Fe5O12, YIG) is an electrically insulating ferrimagnet with an ordering temperature of 560 K. Due to the extremely low magnetic damping (Gilbert damping parameters down to a few 10 ppm) and the small coercive fields, YIG and related magnetic garnets are now used in various high-frequency applications. In addition, these materials are very interesting because of their outstanding properties for basic research in the field of magnonics and spin electronics. However, mostly YIG single crystals and planar thin films are currently used. The fabrication and properties of more complex, 3-dimensional (e.g. curved or tube-like) thin-film structures of YIG or YIG-based heterostructures have not been studied experimentally, although very interesting properties have been predicted.In the framework of this project, we explore this interesting field by establishing the synthesis of YIG layers by means of atomic layer deposition (ALD). ALD is based on successive, self-limited surface reactions and, thus, allows the conformal coating of arbitrarily shaped surfaces. While the ALD of (binary) oxide thin films is already routinely used in the semiconductor industry, two ALD cycles must be combined to produce ternary compounds such as Y3Fe5O12. Therefore, the successful atomic layer deposition of YIG–or more generally of garnet thin films–is also an interesting technological challenge. By combining established ALD processes, we want to produce nano-laminates in which chemically stable binary constituents (Y2O3 and Fe2O3 for YIG) are stacked in a thin-film heterostructure. After a heat treatment, the nano-laminates are converted into the desired material. First, we will establish the nano-laminate process for Y3Al5O12 (YAG), since Al2O3 ALD is particularly robust; it is considered the ALD reference process. Afterwards, we will transition from YAG to YIG. The magnetic properties of the layers are quantified by magnetometry and magnetic resonance investigations. In combination with the ALD process for metallic Pt, YIG/Pt multilayers can be deposited on arbitrarily shaped surfaces. Such heterostructures are very interesting for experiments with pure spin currents. Here, we want to investigate the influence of local curvature or topology on spin transport by means of spin-Hall magnetoresistance experiments.In summary, the proposed atomic layer deposition of yttrium iron garnet provides the base for the production of modern, three-dimensional nanostructures from this special material and, thus, enables a large number of future (spin transport) experiments.