We prepared the ordered phase of FePt alloy at a low annealing temperature by adding Cu to FePt. The ordering of FePtCu film starts at an annealing temperature of 300°C or lower, whereas FePt and FePtAg films do not form the ordered phase at 300°C. By annealing at 300°C, the coercivity of the FePtCu film is increased to around 4.5 kOe. In the FePtCu film, the added Cu and FePt form a ternary alloy before and after annealing, whereas the FePtAg is decomposed into FePt and Ag phases by annealing at temperatures higher than 400°C. Comparison of the FePtCu film with the FePtAg film shows that the formation of a thermodynamically stable FePtCu ternary alloy is important for reducing the ordering temperature.
