Néel type skyrmions formation in nanodots and antidot arrays.

Abstract

Magnetic skyrmions in ferromagnetic materials are mainly stabilized by the interplay of several magnetic energy contributions, i.e. exchange, dipole, anisotropy, and Zeeman. In particular, the asymmetric Dzyaloshinskii-Moriya exchange interaction (DMI) introduces chiral canting between neighboring spins and favors skyrmion stability [1]. Skyrmions are particle-like chiral spin textures found in magnetic films and patterned nanostructures with out-of-plane anisotropy and are considered to be potential candidates as information carriers in next-generation data storage devices [2]. The challenge of the experimental study of skyrmions is to find an efficient technique for forming stable skyrmions. In particular, the outstanding issues are the reproducible generation, stabilization, and confinement of skyrmions at room temperature [2,3,4].It is well known that various magnetic textures can be stabilized by geometrical confinement using artificial nanostructures, however, there are several key challenges like reproducible skyrmion formation that still need to be addressed. We present two methods of skyrmions formation in nanodots and antidots arrays. For these first structures, we have shown the formation of skyrmion using the tip of a magnetic force microscope [3], and during the remagnetization process for antidots arrays [4].Here, we present the results of the investigation of a skyrmion formation in Pt/Co/Au nanodots. We demonstrate that the high magnetic momentum probe induces individual skyrmions during the scan. A specific path of the MFM tip causes a systematic change in the state of the magnetic domains during scanning. The process of annihilation of remaining domains is ruled by magnetostatic interactions where the magnetic domains are simultaneously repelled from the edges of the nanodots and from the tip field. Micromagnetic simulations have shown that specific conditions restricting the movement of magnetic domains must be met in order to form the magnetic skyrmion [3].In this work, we present a method to form nanometer-sized magnetic skyrmions in an array of magnetic topological defects in the form of an antidot lattice. In particular, the introduction of the holes in a thin magnetic film modifies the spatial distribution of the effective field, which has a profound influence on the formation mechanism of the skyrmions. The position of skyrmion formation was recognized at the saddle point of the lattice as a result of the spatial distribution of the effective field. With micromagnetic simulations, we elucidate the steps of the skyrmion formation process and showed that this process depends on the antidot lattice parameters. This behavior is confirmed with scanning transmission x-ray microscopy measurements [4].The work was supported by National Science Centre of Poland, Projects Nos. UMO-2017/27/N/ST3/00419 and UMO-2018/30/Q/ST3/00416. **