Local control of magnetic damping in ferromagnetic/non-magnetic bilayers by interfacial intermixing induced by focused ion-beam irradiation

The influence of interfacial intermixing on the picosecond magnetization dynamics of ferromagnetic/non-magnetic thin-film bilayers was studied. Low-dose focused-ion-beam irradiation was used to induce intermixing across the interface between a 10 nm Ni₈₁Fe₁₉ layer and a 2-3 nm capping layer of either Au or Cr. Time-resolved magneto-optical Kerr effect was used to study magnetization dynamics as a function of ion-beam dose. With an Au cap, the damping of the un-irradiated bilayer was comparable with native Ni ₈₁Fe₁₉ and increased with increasing ion dose. In contrast, for Ni₈₁Fe₁₉/Cr the damping was higher than that for native Ni₈₁Fe₁₉, but the damping decreased with increasing dose.