  In this letter we calculate the energies corresponding to the different
magnetic phases present in a ferromagnetic cylinder by means of analytical
calculations. From the comparison of these energies, it is possible to
construct magnetic phase diagrams as a function of the uniaxial anisotropy of
the sample and the external magnetic field applied. As proof of concept, we
analyzed the magnetic phase diagrams for a cobalt dot of 240 nm in diameter and
70 nm in length, with an easy axis parallel to the dot axis, and with a
magnetic field applied towards or perpendicular to this axis. From these
diagrams we have obtained the stability regions for a Bloch skyrmion (Sk), a
vortex core (VC) and a ferromagnetic (F) configuration, which can point in any
$\psi$ direction. Our results provide a pathway to engineer the formation and
controllability of a skyrmion in a ferromagnetic dot to different anisotropy
constants and magnetic fields.
