Structural order related to the magnetic anisotropy in epitaxial (111) CoPt3 alloy films

(111) CoxPt1-x epitaxial films (0.25 less than or equal to x less than or equal to 0.33) grown on a (0001) Ru buffer at temperatures ranging from 500 to 800 K were investigated. The dependence of the perpendicular magnetic anisotropy on the growth temperature is clearly related to the structural state of the alloy films. The largest perpendicular anisotropy found in a film grown at 690 K is correlated with the existence of a compressive strain resulting from preferential heteroatomic correlations oriented along the growth direction [111], driven by both Pt surface segregation and associated dominant surface diffusion. By contrast, the observation of L1(2) long-range chemical ordering in a film grown at 800 K, favoured by an increase of volume diffusion, is accompanied by the disappearance of perpendicular anisotropy.