  Phases of matter are ubiquitous with everyday examples including solids and
liquids. In reduced dimensions, particular phases, such as the two-dimensional
(2D) hexatic phase and corresponding phase transitions occur. A particularly
exciting example of 2D ordered systems are skyrmion lattices, where in contrast
to previously studied 2D colloid systems, the skyrmion size and density can be
tuned by temperature and magnetic field. This allows us to drive the system
from a liquid phase to a hexatic phase as deduced from the analysis of the
hexagonal order. Using coarse-grained molecular dynamics simulations of soft
disks, we determine the skyrmion interaction potentials and we find that the
simulations are able to reproduce the full two-dimensional phase behavior. This
shows that not only the static behavior of skyrmions is qualitatively well
described in terms of a simple two-dimensional model system but skyrmion
lattices are versatile and tunable two-dimensional model systems that allow for
studying phases and phase transitions in reduced dimensions.
