  Nitrogen-vacancy magnetic microscopy is employed in quenching mode as a
non-invasive, high resolution tool to investigate the morphology of isolated
skyrmions in ultrathin magnetic films. The skyrmion size and shape are found to
be strongly affected by local pinning effects and magnetic field history.
Micromagnetic simulations including static disorder, based on a physical model
of grain-to-grain thickness variations, reproduce all experimental observations
and reveal the key role of disorder and magnetic history in the stabilization
of skyrmions in ultrathin magnetic films. This work opens the way to an
in-depth understanding of skyrmion dynamics in real, disordered media.
