Several regions of a 30 nm thick Ni80Fe20 (permalloy) thin film have been implanted using a focused ion-beam system with varying doses of Ga ions. Changes to their magnetization reversal have been investigated by Lorentz microscopy. Implantation with a dose of 1015 Ga+ cm-2 and 1016 Ga+ cm-2 has increased coercivity of the implanted region while no difference has been observed with a dose of 1014 Ga+ cm-2. Domain wall pinning was shown to be a major mechanism for the increase in coercivity. Also changes to the lattice parameter, composition, thickness and grain size in relation to magnetic properties were investigated using various transmission electron microscopy techniques. The lattice parameter change within the implanted region indicates that the stress can be a major contributor to the increase in coercivity. Relative contributions of changes in other factors such as Ni/Fe ratio, thickness, and grain size within the implanted area have also been discussed. © 2002 American Institute of Physics.