  A magnetic skyrmion is a topological object that can exist as a solitary
embedded in the vast ferromagnetic phase, or coexists with a group of its
"siblings" in various stripy phases as well as skyrmion crystals (SkXs).
Isolated skyrmions and skyrmions in an SkX are circular while a skyrmion in
other phases is a stripe of various forms. Unexpectedly, the sizes of the three
different types of skyrmions depend on material parameters differently. For
chiral magnetic films with exchange stiffness constant $A$, the
Dzyaloshinskii-Moriya interaction (DMI) strength $D$, and perpendicular
magnetic anisotropy $K$, $\kappa\equiv\pi^2D^2/(16AK)=1$ separates isolated
skyrmions from condensed skyrmion states. In contrast to isolated skyrmions
whose size increases with $D/K$ and is insensitive to $\kappa\ll1$ and stripe
skyrmions whose width increases with $A/D$ and is insensitive to $\kappa\gg1$,
the size of skyrmions in SkXs is inversely proportional to the square root of
skyrmion number density and decreases with $A/D$. This finding has important
implications in our search for stable smaller skyrmions at the room temperature
in applications.
