Control of c-axis orientation of L1-FePd in dual-phase-equilibrium FePd/Fe thin films

This work establishes a method of controlling the c-axis-oriented structure of α-Fe (soft magnetic)/L10-FePd (hard magnetic) thin films in the dual-phase compositional region in thermal equilibrium. Two types of thin films were prepared; one is a single-layered thin film, and the other is a multilayered film, [FePd(x nm)/Fe(5 nm)]n (x: thickness, n: the number of multilayers), both of which are deposited on silica glass substrates. For single-layered films, the ordering process is retarded by phase separation that requires long-range diffusion. In this case, the ⟨111⟩ oriented domains preferentially grow from the film surface, and the c-axis-oriented structure is not obtained. On the contrary, for multilayered films, each FePd layer can undergo ordering without phase separation subject to the constraint of strong biaxial tensile stress resulting from the difference in the thermal contractions between Fe/FePd film and the silica glass substrate. Consequently, the L10 domains with c-axis orientation in the normal direction of the film surface are preferentially formed in the initial amorphouslike structure, eventually leading to the desired c-axis-oriented structure.