The present disclosure relates to a method for fabricating an ion-implanted bit-patterned medium. The method includes providing a medium, the medium having a magnetic layer and a substrate and the magnetic layer includes migrating components. The method further includes forming a patterned mask layer on the surface of the magnetic layer and then ion-implanting the medium through the patterned mask layer, wherein the exposed portions of the magnetic layer comprise trench regions, the covered portions of the magnetic layer comprise island regions, and the transition areas between the trench regions and the island regions comprise boundary regions, wherein the island regions have more favorable magnetic properties than the trench regions. The method also includes annealing the medium, wherein the migrating components diffuse from inside the island regions towards the trench regions.