Perpendicular magnetic anisotropy and magnetization of L1_0 FePt/FeCo bilayer films

摘要

Fe_(40)Co_(60) epitaxial thin films are prepared on L1_0 ordered Fe_(60)Pt_(40) underlayer by ultrahigh vacuum multiple dc-sputtering systems. Magnetic properties of the Fe_(60)Pt_(40) (10nm)/Fe_(40)Co_(60) (t nm) bilayer films are investigated. When the FeCo thickness is less than 3 nm, the easy magnetization axis of FePt/FeCo bilayer film is perpendicular to the film plane. Compared with FePt/Fe and FePt/Co films, FePt/FeCo bilayer films possess not only higher anisotropy field H_k but also larger magnetic anisotropy energy K_u, which may be due to the perpendicular magnetic anisotropy yielded by the tetragonal distorted FeCo layer on FePt, while the magnetic easy axes of Fe and Co layers lie in the film plane. Meanwhile, saturation magnetization of FePt/FeCo film increases reasonably because of the high M_s value of FeCo component. These results indicate that the FePt/FeCo bilayer films which possess both large magnetic anisotropy energy K_u and high saturation magnetization M_s have great potential for using as the magnetic recording media, and also give a clue to develop a new type of permanent magnet without rare-earth metals.