The stability of a skyrmion in a nanotube

We study the stability of a skyrmion in a nanotube by using micromagnetic simulations. We find that skyrmions can exist stably in a nanotube within a moderate magnetic field range when the magnetic field is perpendicular to the center axis of the nanotube. In nanotubes the shape of the skyrmion is elliptical. The semimajor and semiminor axes of the ellipse depend on the magnetic field and the angular position of skyrmion. When the skyrmion has an angular displacement from the direction of magnetic field, its shape and size change greatly with the angular position of skyrmion. Also the topological number is dependent on the angular position of skyrmion. When the angular position of skyrmion reaches a critical value, the skyrmion annihilates. The critical angle that skyrmion can survive is not affected by the circular current density, but depends on the radius of nanotube and the strength of magnetic field.