Lisa-Marie Kern
Recent advancements in current- and laser-based spin manipulation have greatly improved the ability to generate, annihilate, and move magnetic skyrmions in ferromagnetic multilayer systems [1–3]. For example, the generation of nanoscale skyrmions has now reached the picosecond timescale [2,3]. However, these methods suffer from a stochastic spatial distribution of the skyrmions created. In view of scientific and practical application of magnetic skyrmions, a precise control of their nucleation site is typically required.
Here, we present two independent approaches we have recently developed:
First, we show that patterned reflective masks behind a thin magnetic film can be designed to locally tailor the optical excitation amplitudes reached, leading to spatially controlled skyrmion nucleation on the nanometer scale [4]. Second, by predefining the magnetic anisotropy landscape employing He+-ions, we have introduced a new experimental platform for deterministic generation and motion of magnetic skyrmions with nanometer-scale control [5].
Transforming skyrmion generation into a deterministic, repeatable process is also crucial for time-resolved experiments to follow the dynamics of the skyrmion formation. Here, we show first results of time-resolved imaging of the magnetization dynamics induced at an artificial nanometer-scale anisotropy defect by current-generated spin–orbit torque in a chiral ferromagnetic multilayer. Similar defects have previously been used as nucleation sites in experiments [2,5] and simulations [6]. In concert with micromagnetic simulations, we observe very different response of the local spin system to the nanosecond-pulsed excitation in dependence of the applied field. The dynamics observed comprise skyrmion shedding, skyrmion formation, and more complex skyrmion instabilities.
Based on our results, we aim to understand the magnetization dynamics at an artificially created nucleation site within the first instances during and after excitation. Understanding the skyrmion formation process, transiently involved textures and fundamental speed and size limits might enable further research on topological textures in general.
[2] Büttner et al., Nat. Nanotech 12, 1040–1044 (2017).
[3] Büttner et al., Nat. Mater. 20, 30–37 (2021).
[4] Kern et al., Phys. Rev. B 106, 054435 (2022).
[5] Kern et al., Nano Lett. 22, 10, 4028-4035 (2022).
[6] Everschor-Sitte et al., New J. Phys. 19 092001 (2017).