Effect of Au Cap Layer on the Magnetic Properties and the Microstructure for FePt Thin Films

[[abstract]]We have investigated the effect of interfacial diffusion on the magnetic properties of Au∕Fe51Pt49 bilayer thin films. The samples were prepared in two stages. First, an ordered Fe51Pt49 continuous thin film was sputtered on a quartz substrate. Then an aurum cap layer was deposited onto the Fe51Pt49 film at room temperature, followed by a postannealing at 300–800°C to promote the interfacial diffusion. A high coercivity of 23.5 kOe was achieved in the isotropic polycrystalline FePt-based film. Transmission electron micrographs indicate that the bilayer sample exhibits Ll0 ordered FePt grains with a diameter of about 20 nm, which were partially isolated by Au phase. We consider that the isolation of FePt Ll0 grains and the grain refining effect can be two contributory factors for the enhanced coercivity