  Investigations of the complex behavior of the magnetization of manganese
arsenide thin films due to defects induced by irradiation of slow heavy ions
are presented. In addition to the thermal hysteresis suppression already
highlighted in M. Trassinelli et al., Appl. Phys. Lett. 104, 081906 (2014), we
report here on new local magnetic features recorded by a magnetic force
microscope at different temperatures close to the characteristic sample phase
transition. Complementary measurements of the global magnetization measurements
in different conditions (applied magnetic field and temperatures) enable to
complete the film characterization. The obtained results suggest that the ion
bombardment produces regions where the local mechanical constraints are
significantly different from the average, promoting the local presence of
magneto-structural phases far from the equilibrium. These regions could be
responsible for the thermal hysteresis suppression previously reported,
irradiation-induced defects acting as seeds in the phase transition.
