Skyrmions in antiferromagnetic and highly anisotropic environments

在这个项目中，我们将利用自旋极化扫描隧道显微镜(SP-STM)的原子分辨能力来(I)制备反铁磁(AFM)薄膜中的Skyrmions并直接成像，(Ii)研究尚未探索的强各向异性过渡金属氧化物(TMO)中的高度各向异性手性自旋结构和磁孤子，以及(Iii)探索磁畴壁和Skyrmions如何与电流相互作用。为了实现这些目标，我们将以原子分辨率成像真实空间的自旋结构，并研究外部刺激的影响，例如STM针尖施加的全局外部磁场或局部电场脉冲。此外，我们还将研究单个分子或原子缺陷对磁天子的形成、大小、形状和迁移率的影响。具有铁磁交换作用的WP(I)-Skyrmions(FM-SKY)已经在实验和理论上得到了深入的研究。相比之下，具有AFM交换的材料(AFM-SKY)中的Skyrmions迄今只在模型计算的框架内被提出，这些材料被预测在没有任何Skyrmion Hall效应的情况下表现出更强的自旋力矩。我们将与基尔大学(海因策)的密度泛函专家合作，研究原子力显微镜薄膜中的天米子形成。除了具有横向AFM交换的薄膜，即所谓的G型反铁磁体，我们还将对层状反铁磁体进行实验，其中单个原子层耦合FM，但层间耦合是AFM。一旦被发现，我们将研究全球外部或局部STM感应场如何产生、操纵或湮灭Skyrmions。与FZ Jülich(Lounis)合作，我们还将研究单个Skyrmions的性质或它们之间的相互作用如何响应故意沉积的吸附原子或分子。到目前为止所研究的WP(II)-磁性Skyrmion系统总是由具有相当各向同性交换机制的二维薄膜组成。最近，我们在重面心立方(001)表面外延生长的一维TMOS中发现了强各向异性的手征磁性结构。在FZ Jülich(Lezaic/BlüGel)的合作下，我们将研究导致这些螺旋自旋结构的间接磁交换耦合。为此，我们将研究磁结构对外部磁场或温度升高的响应。此外，我们将成像在这些自旋螺旋线中的磁区壁(孤子)的传播。WP(III)-电荷电流对磁天子施加了极大的自旋扭矩。我们将通过STM诱导的远程分子异构化研究来研究电荷和自旋在单个Skyrmions中的输运，并将结果与传统的磁区和磁区壁进行比较。这项新技术允许以前所未有的分辨率询问单个缺陷的影响。

Within this project, we will make use of the atomic-resolution capabilities of spin-polarized scanning tunneling microscopy (SP-STM) to (i) prepare and directly image skyrmions in antiferromagnetic (AFM) films, (ii) to study highly anisotropic chiral spin structures and magnetic solitons in yet unexplored strongly anisotropic transition metal oxides (TMO), and (iii) to probe how magnetic domain walls and skyrmions interact with electric currents. Towards these goals, we will image the real-space spin structure with atomic resolution and study the impact of external stimuli, such as global external magnetic fields or local electric field pulses applied by the STM tip. Furthermore, we will investigate the effects of single molecular or atomic defects on the formation, size, shape, and mobility of magnetic skyrmions. WP(i) — Skyrmions with a ferromagnetic exchange interaction (FM-Sky) have already been intensively investigated both experimentally and theoretically. In contrast, skyrmions in materials with AFM exchange (AFM-Sky), which are predicted to exhibit an even stronger spin torque without any skyrmion Hall effect, have so far been only proposed within the framework of model calculations. In cooperation with experts in DFT from the University of Kiel (Heinze) we will investigate skyrmion formation in AFM thin films. In addition to films with lateral AFM exchange, so-called “G-type” antiferromagnets, we will also perform experiments on layered antiferromagnets where individual atomic layers couple FM but the inter-layer coupling is AFM. Once discovered we will investigate how skyrmions can be generated, manipulated, or annihilated by global external or local STM-induced fields. In cooperation with the FZ Jülich (Lounis) we will also study how the properties of single skyrmions or the interactions between them respond to intentionally deposited adatoms or molecules. WP(ii) — Magnetic skyrmion systems investigated so far always consisted of two-dimensional films with rather isotropic exchange mechanisms. Recently, we discovered strongly anisotropic chiral magnetic structures in one-dimensional TMOs epitaxially grown on heavy fcc(001) surfaces. In cooperation with FZ Jülich (Lezaic/Blügel) we will investigate the indirect magnetic exchange coupling responsible for these spiral spin structures. Towards this purpose, we will study how the magnetic structure responds to external magnetic fields or an increased temperature. Furthermore, we will image the propagation of domain walls (solitons) in these spin spirals. WP(iii) — Charge currents exert an extraordinary large spin torque on magnetic skyrmions. We will investigate charge and spin transport through single skyrmions by means of STM-induced remote molecule isomerization studies and compare the results to conventional domains and domain walls. This novel technique allows to interrogate the effects of single defects with unprecedented resolution.