Deterministic Generation and Guided Motion of Magnetic Skyrmions by Focused He$^+$-Ion Irradiation

Abstract

Magnetic skyrmions are quasiparticles with non-trivial topology, envisioned to play a key role in next-generation data technology while simultaneously attracting fundamental research interest due to their emerging topological charge. In chiral magnetic multilayers, current-generated spinorbit torques or ultrafast laser excitation can be used to nucleate isolated skyrmions on a picosecond timescale. Both methods, however, produce randomly arranged skyrmions, which inherently limits the precision on the location at which the skyrmions are nucleated. Here, we show that nanopatterning of the anisotropy landscape with a He + -ion beam creates well-defined skyrmion nucleation sites, thereby transforming the skyrmion localization into a deterministic process. This approach allows to realize control of individual skyrmion nucleation as well as guided skyrmion motion with nanometer-scale precision, which is pivotal for both future fundamental studies of skyrmion dynamics and applications.Magnetic skyrmions are topological quasiparticles that can be as small as a few nanometers. [1][2][3] During the last decade, research on magnetic skyrmions attracted interest from scientific 4,5 and industrial 6 research communities due to the skyrmion's fascinating properties emerging from its topological charge. They can exist in thin film materials with perpendicular magnetic anisotropy (PMA) and are stabilized by stray fields and the Dzyaloshinskii-Moriya interaction (DMI). [7][8][9][10][11][12][13] In particular, skyrmions in chiral magnetic multilayer systems can occur as isolated particle-like textures at room temperature and in a low external magnetic field regime down to zero field. [13][14][15] Great advances have been reported in generating, annihilating and shifting skyrmions via spin-orbit torques (SOT) induced by electric currents inside a suitable magnetic racetrack. 3,12,14,[16][17][18][19][20] Moreover, recent studies have revealed that faster and potentially more energy-efficient skyrmion generation is feasible by replacing current pulses with femtosecond laser pulses, allowing optical nucleation even with a single laser pulse.