Microstructural changes during annealing of FePd-based thin films

The microstructural changes in magnetron sputtered Fe–Pd thin films during annealing at 400–500 °C have been studied by transmission electron microscopy. Room-temperature deposition produced disordered Fe–Pd phase with (111)-twinned grains approximately 18 nm in size. L10-type ordering was complete for annealing at 450 and 500 °C after 1.8 ks, accompanied by grain growth (40–70 nm). The ordered FePd grains contained (111)-twins rather than {101}-twins typical of bulk ordered FePd. A critical grain size that is larger than the maximum grain size of 70nm observed here may exist, below which the transformation-strain-induced {101}-polytwin formation is suppressed in L10-ordered FePd. The metallic Pt overlayers and the Ti and NiCr underlayers selected here produced detrimental dissolution (Pt into Fe–Pd phases) and did not prevent precipitation reactions between Pd and the Si substrate during annealing.