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

Y3Fe5O12(Y3Fe5O12，YIG)是一种有序温度为560K的电绝缘铁磁体，由于其极低的磁损耗(Gilbert衰减系数低至10ppm)和小的矫顽场，YIG及其相关的磁性石榴石目前被用于各种高频应用。此外，这些材料非常有趣，因为它们在磁振子和自旋电子学领域的基础研究中具有突出的性能。然而，目前使用的主要是YIG单晶和平面薄膜。YIG或YIG基异质结构中更复杂的三维(如弯曲或管状)薄膜结构的制备和性质还没有被实验研究过，尽管已经预测了非常有趣的特性。在这个项目的框架内，我们通过建立原子层沉积(ALD)的方法来建立YIG层的合成来探索这个有趣的领域。ALD是基于连续的、自限的表面反应，因此，允许对任意形状的表面进行保形涂层。虽然(二元)氧化物薄膜的ALD已经在半导体工业中被常规使用，但必须将两个ALD循环结合起来才能产生三元化合物，如Y3Fe5O12。因此，成功的YIG原子层沉积--或者更广泛地说，石榴石薄膜--也是一个有趣的技术挑战。通过结合已建立的ALD工艺，我们想要制造出化学稳定的二元成分(Y203和YIG的Fe2O3)堆积在薄膜异质结构中的纳米层压板。经过热处理后，纳米层压板被转化为所需的材料。首先，我们将建立Y3Al5O12(YAG)的纳米层压工艺，因为Al_2O_3 ALD特别坚固；它被认为是ALD的参考工艺。之后，我们将从YAG过渡到YIG。通过磁测量和磁共振研究，量化了各层的磁性。结合金属铂的ALD工艺，可以在任意形状的表面上沉积YIG/铂多层膜。这种异质结构对于纯自旋流的实验非常有趣。在这里，我们想要通过自旋霍尔磁阻实验来研究局域曲率或拓扑结构对自旋输运的影响。综上所述，本文提出的原子层沉积方法为从这种特殊材料制备现代三维纳米结构提供了基础，从而使未来的大量(自旋输运)实验成为可能。

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.