Thermal stability of L11 ordered phase in CoPt-alloy thin films formed on MgO(111) single-crystal substrates

Metastable L1(1) ordered CoPt(111) epitaxial thin films with the order degrees around 0.3 are formed on MgO(111) single-crystal substrates at 300 degrees C by using an ultra-high vacuum radio-frequency magnetron sputtering system. The effects of annealing after film formation on the structure and the magnetic properties are investigated. As the annealing temperature increases, the order degree gradually decreases. At 600 degrees C, the ordered phase disappears and the film changes to disordered structure. CoPt(111) epitaxial films with disordered structure are also prepared at room temperature and 600 degrees C and then these films are annealed at 300 degrees C. However, ordered phase formation is not recognized in the films. The metastable L1(1) ordered phase is preferentially formed when the film is deposited at a temperature of 300 degrees C. Annealing a film with disordered structure at 300 degrees C does not promote L1(1) ordering. The CoPt films involving L1(1) ordered structure show perpendicular magnetic anisotropies, whereas the disordered films have in-plane anisotropies. The magnetic properties are influenced by the order degree.