  Understanding the nature of magnetic interactions in ultra-small magnetic
ensembles and their intrinsic properties is vital to uncover the dynamics
therein. In this study we reveal the spin dynamics of hexagonally arranged Fe
atoms on metallic surface that are triggered by magnetic pulse. The switching
process among various spin configurations and their relative magnetic order is
tuned by the amplitude and duration of the magnetic pulse. Even more we observe
a parity effect in the switching time as the size of the cluster varies in
which even number of Fe atoms shows faster dynamics. The changes in the
multistable magnetic states and switching times are explained by using the
relaxation of the exchange and anisotropy energies in time.
