Skyrmions in antiferromagnetic and highly anisotropic environments

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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.