Microstructure study of CoPt thin film with phase change from A1 → L11 → A1 → L10

In this study, 50-nm-thick CoPt film was sputtered on MgO(111) substrate at substrate temperature (Ts) from room temperature (RT) to 750 °C. Within the temperature range, the phase evolves in the sequence of A1 (disordered) at RT, L11 (ordered), A1, and L10 (ordered) at 750 °C. L11-ordering occurred in the range of 250 °C ≦ Ts ≦ 500 °C induces strong perpendicular magnetic anisotropy. Microstructure results indicate that the CoPt grain size increases gradually from about 10 to 50 nm as Ts increases from RT to 600 °C. Grain size significantly increases to larger than 70 nm as Ts > 600 °C, which is attributed to the occurrence of L10-ordering. Further increase Ts to 750 °C, isotropic L10-(111) textured CoPt forms with a higher Hc of 5.0 kOe. Detailed discussion of relation between magnetic behaviors and microstructure is given.