  Magnetic skyrmions are topologically non-trivial spin whirls that may not be
transformed continuously into topologically trivial states such as
ferromagnetic spin alignment. In recent years lattice structures composed of
skyrmions have been discovered in certain bulk chiral magnets with
non-centrosymmetric crystal structures. The magnetic phase diagrams of these
materials share remarkable similarities despite great variations of the
characteristic temperature, field, and length scales and regardless whether the
underlying electronic state is that of a metal, semiconductor, or insulator.
