Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Magnetic skyrmions and skyrmion clusters in the helical phase of
  Cu$_2$OSeO$_3$   Skyrmions are nanometric spin whirls that can be stabilized in magnets
lacking inversion symmetry. The properties of isolated skyrmions embedded in a
ferromagnetic background have been intensively studied. We show that single
skyrmions and clusters of skyrmions can also form in the helical phase and
investigate theoretically their energetics and dynamics. The helical background
provides natural one-dimensional channels along which a skyrmion can move
rapidly. In contrast to skyrmions in ferromagnets, the skymion-skyrmion
interaction has a strong attractive component and thus skyrmions tend to form
clusters with characteristic shapes. These clusters are directly observed in
transmission electron microscopy measurements in thin films of Cu$_2$OSeO$_3$.
Topological quantization, high mobility and the confinement of skyrmions in
channels provided by the helical background may be useful for future
spintronics devices.

25
The categories of this paper are: patt-sol
9
The categories of this paper are: nlin
28
The categories of this paper are: alg-geom
6
The categories of this paper are: astro-ph
15
The categories of this paper are: nucl-ex
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs
31
The categories of this paper are: ao-sci
8
The categories of this paper are: hep-ex
16
The categories of this paper are: stat
24
The categories of this paper are: dg-ga
20
The categories of this paper are: acc-phys
7
The categories of this paper are: hep-th
5
The categories of this paper are: gr-qc
19
The categories of this paper are: eess
32
The categories of this paper are: atom-ph