Motion and Dynamics of Nanoscale Skyrmions in Ferrimagnetic Multilayers

磁skyrmions是拓扑保护的手性自旋纹理与新的特性，这是非常有前途的未来的数据存储和信息技术的应用，如所谓的赛道存储器。在过去的几年里，这些旋转的磁性模式已经在各种材料中被发现和广泛研究。最近，实验研究已经证实，即使在室温及以上的磁性多层膜中的skyrmions的稳定性。然而，基于skyrmion的设备的实际实现存在根本性的限制。特别地，铁磁体中的skyrmion受到不期望的拓扑效应，即skyrmion霍尔效应，其引起相对于电流方向的横向运动，并且因此可以导致传播速度大大降低，甚至导致skyrmion在器件边缘处的湮灭。考虑到这些限制，基于skyrmion的存储器设备的性能和可靠性将不具有竞争力。然而，第一个理论和实验工作已经证明了一个显着减少的skyrmion霍尔效应在亚铁磁多层膜，其中角动量的补偿。在这一点上，研究仍处于起步阶段，有一个系统的实验工作，对不同组成的亚铁磁性多层系统的巨大需求。因此，本研究项目的主要目标是设计skyrmion以超过1000 m/s的速度移动，并将其空间范围缩小到10 nm或更小。为此，将详细了解skyrmion速度对尺寸，电流密度，材料成分和缺陷浓度的依赖性。此外，我们还将利用宽带微波吸收谱、自旋扭矩铁磁共振和空间分辨布里渊光散射谱等技术研究亚铁磁性稀土/过渡金属复合材料中skyrmion态的动态激发。结果将提供有关潜在的磁相互作用的有价值的信息，从而允许进一步优化的多层设计方面的竞争性设备的实现。在这方面，将开发新的技术和协议，用于可重复的生成和可靠的检测单个skyrmions。

Magnetic skyrmions are topologically protected chiral spin textures with novel characteristics which are highly promising for future data storage and information technology applications, such as so-called racetrack memories. During the past years, these swirling magnetic patterns have been discovered and extensively studied in a wide range of materials. Very recently, experimental studies have confirmed the stabilization of skyrmions in magnetic multilayers even at room temperature and above. However, there exist fundamental limitations to the practical realization of skyrmion-based devices. In particular, skyrmions in ferromagnets are subject to an undesirable topological effect, the skyrmion Hall effect, which causes a transverse motion with respect to the current flow direction and thus can result in a strongly reduced propagation velocity or even in the annihilation of skyrmions at the device edges. In consideration of these limitations, the performance and reliability of a skyrmion-based memory device would not be competitive. However, first theoretical and experimental works have already demonstrated a significant reduction of the skyrmion Hall effect in ferrimagnetic multilayers, where the angular momentum is compensated. At this point, research is still in its infancy and there is a great need for systematic experimental work on ferrimagnetic multilayer systems of different compositions. Therefore, the main goal of this research project is to engineer skyrmions to move at velocities exceeding 1000 m/s and reducing their spatial extent to 10 nm or less. For this purpose, a detailed understanding of the skyrmion velocity dependence on the size, current density, material composition and concentration of defects will be developed. In addition, the dynamic excitations of skyrmion states in ferrimagnetic rare earth/transition metal composite materials will be investigated by means of broadband microwave absorption spectroscopy, spin-torque ferromagnetic resonance and spatially-resolved Brillouin light scattering spectroscopy. The results will provide valuable information about the underlying magnetic interactions and thereby allow for a further optimization of the multilayer design with regard to the realization of competitive devices. In this respect, novel techniques and protocols for a reproducible generation and reliable detection of individual skyrmions will be developed.