  Knowledge of free energy barriers separating different states is critically
important for assessment of long-term stability of information stored in
magnetic devices. This information, however, is not directly accessible by
standard simulations of microscopic models because of the ubiquitous time-scale
problem, related to the fact that the transitions among different free energy
minima have character of rare events. Here we show that by employing the
metadynamics algorithm based on suitably chosen collective variables, namely
helicity and circulation, it is possible to reliably recover the free energy
landscape. We demonstrate the effectiveness of the new approach on the example
of vortex nucleation process in magnetic nanodot with lowered spatial symmetry.
With the help of reconstructed free energy surfaces (FES) we show the origin of
the symmetry broken vortex nucleation, where one polarity of the nucleated
vortex core is preferred, even though only in-plane magnetic field is present.
