Confinement of Skyrmions in Nanoscale FeGe Device-like Structures

Abstract

Skyrmion-based devices have been proposed as a promising solution for low energy data storage. These devices include racetrack or logic structures and require skyrmions to be confined in regions with dimensions comparable to the size of a single skyrmion.Here we examine skyrmions in FeGe device shapes using Lorentz transmission electron microscopy (LTEM) to reveal the consequences of skyrmion confinement in a device-like structure. Dumbbell-shaped elements were created by focused ion beam (FIB) milling 1 to provide regions where single skyrmions are confined adjacent to areas containing a skyrmion lattice. Simple block shapes of equivalent dimensions were also prepared to allow a direct comparison with skyrmion formation in a less complex, yet still confined, device geometry. The impact of applying a magnetic field and varying the temperature on the formation of skyrmions within the shapes was examined. This revealed that it is not just confinement within a small device structure that controls the position and number of skyrmions, but that a complex device geometry changes the skyrmion behaviour, including allowing skyrmions to form at lower applied magnetic fields than in simple shapes. The impact of edges in complex shapes is observed to be significant in changing the behaviour of the magnetic textures formed. This could allow methods to be developed to control both the position and number of skyrmions within device structures.

Geometric phase analysis of magnetic skyrmion lattices in Lorentz transmission electron microscopy images

“…We also hope that this method will be useful to study skyrmion lattices in samples of different geometries as in Ref. [37,38] for example. As the skyrmion lattice tend to align with the edges of the sample, geometric constraints could lead to different arrangements with different deformation fields.…”

Geometric phase analysis of magnetic skyrmion lattices in Lorentz transmission electron microscopy images

“…We also hope that this method will be useful to study skyrmion lattices in samples of different geometries as in Ref. 40,41 for example. As the skyrmion lattice tend to align with the edges of the sample, geometric constraints could lead to different arrangements with different deformation fields.…”

Nucleation of magnetic skyrmions at a notch

“…An efficient generator of Sk should have the following properties: it should not create Sk in waiting mode and create Sk in robust manner under applied control. Nucleation of magnetic Sks on the track with a notch was investigated experimentally [23][24][25][26] and theoretically [27][28][29][30][31][32]. Despite the fact that the works [23][24][25][26][27][28][29][30][31][32] studied systems with different magnetic characteristics, geometries and external conditions, it was shown in all cases that notches may serve as a generator of skyrmions.…”

“…Nucleation of magnetic Sks on the track with a notch was investigated experimentally [23][24][25][26] and theoretically [27][28][29][30][31][32]. Despite the fact that the works [23][24][25][26][27][28][29][30][31][32] studied systems with different magnetic characteristics, geometries and external conditions, it was shown in all cases that notches may serve as a generator of skyrmions. However, these studies considered only one or several notches with fixed geometry, which is not enough for revealing the effect of notch design on Sk nucleation.…”