Topologically nontrivial spin-textures are very promising for the next generation of spintronic devices. These spin textures are topologically protected in the sense, that their magnetization cannot be continuously transformed into the uniform magnetized state. The skyrmion stability mechanism is different in various materials, for instance, Dzyaloshinskii-Moriya interaction or frustrated exchange interactions. Another mechanism that leads to the formation of skyrmions is the competition between the long-range ordered dipolar interaction, perpendicular magnetic anisotropy, and the short-ranged exchange interaction. In addition to the Bloch skyrmions, we demonstrated both experimentally and by means of micromagnetic simultions, that the topologically opposite counterpart, the antiskyrmions can be stabilized by dipolar interactions in Fe/Ir/Gd-based multilayers [1,2].

In this talk, we report on the first experimental observation of higher-order skyrmions and antiskyrmions, which are stabilized by dipolar interactions in a Co/Ni-based multilayer system [3]. We employ Lorentz transmission electron microscope (LTEM) to image a high diversity of higher order skyrmions and antiskyrmions with topological charges between ±10. Our numerical investigations reveal that the Co/Ni based multilayers exhibit a high number of vertical Bloch lines (VBL), which behave like a domain wall within a domain wall, where the magnetization experiences a 180° rotation.

In a next step, we investigate the current-driven motion of higher-order spin-objects. We assume an in-plane current injected directly through the magnetic material. We demonstrate with our micromagnetic modeling that the (anti)skyrmions of different Q exhibit different skyrmion Hall angles, which vanishes with increasing Q.

Furthermore, we demonstrate for the first time, that a high resolution magnetic force microscopy can be employed to reveal vertical Bloch lines, skyrmions and antiskyrmions of different orders [4].

^{[1] Michael Heigl, Sabri Koraltan et al. "Dipolar-stabilized first and second-order antiskyrmions in ferrimagnetic multilayers." Nature Communications 12.1 (2021): 2611.
[2] Sabri Koraltan et al. "Generation and annihilation of skyrmions and antiskyrmions in magnetic heterostructures." Physical Review B 108.13 (2023): 134401.
[3] Mariam Hassan, Sabri Koraltan et al. 2024 - "Dipolar skyrmions and antiskyrmions of arbitrary topological charge at room temperature" - Nature Physics (2024). https://doi.org/10.1038/s41567-023-02358-z
[4] Sabri Koraltan et al. “Revealing vertical Bloch line, skyrmions and antiskyrmions using magnetic force microscopy” 2024, to be submitted}