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

Abstract

Abstract The heat treatment of [Fe/Pt] n multilayer films is a promising approach to form the L1 0 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 L1 0 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 L1 0 grains were relatively small and located at boundaries between larger grains. Measurements of c / a ratio of the L1 0 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.