  We have observed the evolution of phase diagram and vortex pinning using a
single ferromagnet/superconductor bilayer of [Co/Pt]8/Nb through a special
demagnetization procedure. It induces a continuous and reversible change of the
domain width with equal positive/negative domains enabling the observation of
the predicted tunable phase diagram. The tunable domain pattern also
systematically affects vortex pinning. We have determined the dependence of the
activation energy of vortex pinning on domain width, temperature, and magnetic
field.
