Topological Meron-Antimeron Domain Walls and Skyrmions in a Low-Symmetry System

The generation of topologically nontrivial magnetic configurations has been a pivotal topic in both basic and applied nanomagnetism research. Localized noncoplanar magnetic defects such as skyrmions or merons were found to interact strongly with currents, making them interesting candidates for future spintronics applications. So far, mostly systems with a high rotational symmetry have been investigated where skyrmions were axially symmetric. Here, we study a low-symmetry system by spin-polarized scanning tunneling microscopy and an atomistic spin model using parameters based on first-principles calculations. We demonstrate how a delicate balance between energy terms generates both topologically trivial and nontrivial domain walls, depending on their nonequivalent crystallographic direction. The topological walls consist of alternating merons and antimerons, and the topological charge is 1 for every 6-nm length of the wall. The incorporation of holes in the films facilitates the transition from an in-plane ferromagnetic ground state to a spin-spiral state. Both domain walls and spirals transition into isolated elongated magnetic skyrmions in applied magnetic fields. These findings establish low-symmetry systems as a versatile platform for spin-texture engineering.