Formation of FePt nanodots by wetting of nanohole substrates

Large area arrays of FePt nanodots are fabricated on patterned substrates made of SiOx, SiNx and TiNx. The templates have a depth of ∼10 nm and a pitch of ∼20 nm with 18 nm wide holes. FePt is sputtered on the nanohole arrays, then back-etched, leaving a highly ordered array of FePt nanodots behind. To promote phase transformation to the L10 phase, the samples are annealed at temperatures of 550-650° C. During annealing, the FePt strongly dewets SiOx and SiNx substrates, causing sintering and coalescence of the FePt nanodots, but the nanodots remain highly ordered on the TiNx substrate. The nanodot arrays on TiNx are characterized magnetically before and after annealing. The out-of-plane coercivity increases by ∼1 kOe, suggesting partial transformation to the L10 phase. We also show that a capping layer can be sputtered on top of the nanodot arrays prior to annealing to prevent dewetting.