Effect of the A1 to L10 transformation on the structure and magnetic properties of polycrystalline Fe56Pd44 alloy thin films produced by thermal evaporation technique

X-ray diffraction, conversion electron Mössbauer spectroscopy and superconducting quantum interference device magnetometer techniques have been used to characterize the evolution of the microstructure and of the magnetic properties of phase transformation from disordered FePd face-centred cubic (A1) phase, to an ordered phase L10 FePd of tetragonal structure. This study was carried out by isothermally annealing in vacuum at 550 °C, as a function of annealing time, a Fe56Pd44 thin film alloy deposited on silicon substrate. The structural transformations are accompanied by a decrease of the (c/a) ratio and by an increase of the coercive field as a function of annealing time. After 10 min of annealing, the (c/a) ratio is equal to 0.945, which indicates that the disordered FePd phase is completely transformed into the ordered L10 FePd phase. By increasing annealing time, the microstructure of the alloy evolves, antiphase boundaries and twin boundaries develop. In contrast to the relationship most commonly described in the literature, that the highest coercivity corresponds to a two-phase ordered/disordered mixture, in ours studies the maximum value for coercivity corresponds to the fully ordered state. Furthermore, we propose that the high coercivity in these films is due to pinning centres of magnetic domain walls by antiphase boundaries and twin boundaries.