Thickness dependence of structure and magnetic properties of annealed [Fe/Pt] n multilayer films

Abstract

The L 10 FePt phase material has potential applications for magnetic recording and permanent magnets due to its high magnetocrystalline anisotropy energy density. The heat treatment of [Fe/Pt] n multilayer films is one approach to form the L 10 FePt phase at a lower processing temperature, which is highly desirable for its applications. This paper reports the influence of film total thickness (8-100 nm) on the structure and magnetic properties of annealed [Fe/Pt] n multilayer films. A novel technique based on hollow cone dark field transmission electron microscopy is used to determine the L 10 phase fraction and grain size in the annealed films. It was found that the L 10 phase fraction and grain size, ordering, and magnetic properties are strongly dependent on the total film thicknesses. An L 10 FePt phase fraction close to 100% is achieved for a thick [Fe/Pt] n multilayer film (100 nm) annealed at 400 °C for 1 h, while a value of only 36% is achieved for a thin film (8 nm) annealed at the same condition. In this work the L 10 FePt phase nucleation density is also presented. These results suggest that the L 10 phase formation is nucleation limited, and that the subsequent growth of L 10 phase grains also strongly influences the structure and magnetic properties of the annealed films. © 2009 American Institute of Physics.