The influence of periodicity on the structures and properties of annealed [Fe/Pt]n multilayer films

The heat treatment of [Fe/Pt]n multilayer films is a promising approach to form the L10 FePt phase at a reduced temperature, which is of interest for applications as high-density magnetic recording media and high-energy permanent magnets. This paper reports the influence of the bilayer period in the range of 1–18 nm on the microstructure and magnetic properties of annealed polycrystalline [Fe/Pt]n films sputtered onto thermally oxidized Si substrates. The microstructures were characterized by transmission electron microscopy and dynamical conical annular dark field imaging was used to identify the L10 phase grains present in the sample. This ordered phase was only observed in samples annealed at or above 300 °C and was found to have a typical grain size smaller than that of the mostly A1 (fcc) matrix. The majority of the L10 grains were relatively small and located at boundaries between larger grains. Measurements of c/a ratio of the L10 phase indicated an increase in the degree of chemical ordering with as-deposited film period. We also found the coercivity of the annealed polycrystalline multilayer films to increase with the as-deposited period, which is contrary to previous reports in which epitaxial [Fe/Pt]n films were studied.