  Topological spin structures with transformable shapes may have potential
implications on data storage and computation. Here, we demonstrate that a
square cellular skyrmion on an artificial grid pinning pattern can be
manipulated by programmed current pulses. We find that parallel short pulses
could result in the elongation of the skyrmion mainly in the current direction,
while parallel long pulses are able to induce the elongation in the direction
perpendicular to the current due to the intrinsic skyrmion Hall effect.
Consequently, a programmed sequence of parallel pulses could lead to the
transformation of the skyrmion to I-, L-, and Z-shaped polyomino-like
structures without affecting the topological charge. In addition, we find that
orthogonal pulses could lead to the transformation to more complex
polyomino-like structures, including the T-shaped and irregular ones.
Particularly, when a small T-shaped structure is formed, the topological charge
of the system is found to be non-integer due to incomplete compensation of
local topological charge densities; however, the T-shaped structure is stable
on the attractive pinning pattern. Our results offer an effective way to create
polyomino-like spin structures toward functional applications.
