It is well-known that bubble propagation margins for ion-implanted bubble devices depend strongly on ion-implantation conditions. A new ion-implantation method is reported that can significantly improve bubble propagation margins for minor loops with 4 × 4 μm bit cell size. The implantation was done through a Mo thin film layer so that the lattice strain and the anisotropy field change would be more uniform through the depth of the implanted layer. With this method, minor loops can be formed by hydrogen single implantation. Consequently simplification of the implantation process is achieved.