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

¹ Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan
² Graduate School of Fine Arts, Tokyo University of the Arts, 12-8 Ueno-koen, Taito-ku, Tokyo 110-8714, Japan

Abstract

Metastable L1₁ ordered CoPt(111) epitaxial thin films with the order degrees around 0.3 are formed on MgO(111) single-crystal substrates at 300 °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 °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 °C and then these films are annealed at 300 °C. However, ordered phase formation is not recognized in the films. The metastable L1₁ ordered phase is preferentially formed when the film is deposited at a temperature of 300 °C. Annealing a film with disordered structure at 300 °C does not promote L1₁ ordering. The CoPt films involving L1₁ ordered structure show perpendicular magnetic anisotropies, whereas the disordered films have in-plane anisotropies. The magnetic properties are influenced by the order degree.