  Magnetic skyrmions are topological objects, which have recently been observed
in thin films at room temperature. Sub 100-nm sizes and spin polarised current
manipulation make them candidates for high density information storage and
processing. Besides material thickness, skyrmion stability involves many
contributions: ferromagnetic exchange, magnetic anisotropy,
Dzyaloshinskii-Moryia exchange interaction (DMI) and demagnetising energy.
Multidimensional phase diagrams have been reported in the litterature. In this
work we propose a simple two-parameter model, exact for thin films in the
negligible magnetisation limit, e.g. ferrimagnets close to compensation and
synthetic artificial antiferromagnets. It allows to define design rules to
stabilize small diameter skyrmions at room temperature with explicit estimates
of their nucleation and collapse energies. Comparisons to micromagnetic
calculations allow to assess the model quality for non-zero magnetisation and
show good agreement.
