The A1 to L1 transformation in FePt and FeCuPt thin films: Determination of isothermal transformation kinetics from nonisothermal measurements

Time–temperature-transformation diagrams describing the A1 to L10 transformation in 1μm thick FePt and FeCuPt alloy films are constructed from data obtained using nonisothermal differential scanning calorimetry in conjunction with a limited number of isothermal anneals. For the FePt alloys, an increase in Pt content from 45.6 to 52.5 at.% results in a >300× increase in the annealing time needed to reach a fraction transformed of 0.95 at 300 °C. Using geometric corrections, the results are extended to 10 nm thick films, which are found to transform approximately five times more slowly than thicker films.