Fabrication of Electrodeposited FeCuPt Nanodot Arrays Toward $L1_{0}$ Ordering

FeCuPt nanodot arrays were fabricated by electrodeposition onto a nanopore patterned substrate fabricated by electron beam lithography (EBL), for the purpose to manufacture and characterize model bit-patterned media. Addition of Cu to FePt was carried out to accelerate the phase transformation of FePt into the $L1_{0}$ -ordered phase in order to fabricate nanodot arrays with hard and uniform magnetic properties. Composition of the FeCuPt ternary alloy films was optimized by varying applied potential and CuSO4 concentration to form single $L1_{0}$ phase (40–50 at% Pt and ~25 at% Cu). Annealing at 450 °C resulted in the phase transformation from fcc to $L1_{0}$ in FeCuPt ternary alloy films, whereas FePt binary alloy films did not show a phase transformation. Perpendicular coercivities of FeCuPt and FePt were 6 and 1 kOe, respectively, annealing at 450 °C, indicating the formation of the $L1_{0}$ phase with lower annealing temperature by Cu incorporation. FeCuPt nanodot arrays with 20 nm in diameter and 35 nm in pitch were successfully fabricated with the nanopore patterned substrate fabricated by EBL. In addition, cross-sectional transmission electron microscope analysis of FeCuPt nanodot arrays showed clear stacking of the $L1_{0}$ (111) lattice in a perpendicular direction through the growth direction having a single crystal nature, whereas phase transformation was insufficient with FePt nanodot arrays. The collective results have successfully demonstrated the electrochemical fabrication of ultra-fine FePt nanodot arrays with $L1_{0}$ structure by promoting $L1_{0}$ ordering with Cu additions.