  Understanding the physical properties of magnetic skyrmions is important for
fundamental research with the aim to develop new spintronic device paradigms
where both logic and memory can be integrated at the same level. Here, we show
a universal model based on the micromagnetic formalism that can be used to
study skyrmion stability as a function of magnetic field and temperature. We
consider ultrathin, circular ferromagnetic magnetic dots. Our results show that
magnetic skyrmions with a small radius compared to the dot radius are always
metastable, while large radius skyrmions form a stable ground state. The change
of energy profile determines the weak (strong) size dependence of the
metastable (stable) skyrmion as a function of temperature and/or field. These
results can open a path toward the design of optimal materials for skyrmion
based devices.
