Dependence of ordering kinetics of FePt thin films on different substrates

FePt thin films are deposited on SrTiO₃, MgO, and a 2 nm-FeO_x underlayer on an Si substrate at room temperature and then annealed at elevated temperatures. Studies of the L1₀ ordering process in each case show that the ordering temperature for the FePt film on the nonepitaxial Si/FeO_x substrate is ∼150 °C lower than the epitaxial FePt films deposited on MgO and SrTiO₃ substrates. We argue that internal stresses arising from lattice defects and a recrystallizing process as well as thermal strain from differences in thermal expansion between substrate and film are responsible for the differences in ordering kinetics from the A1 to L1₀ phase of FePt on the various substrates.