Influence of post-annealing on the properties of Fe₅₀Pt₅₀ film and submicron size particles

The magnetic properties of a 48 nm thick Fe50Pt50 film and submicron size elements made of the film were investigated. The initial film was grown by DC magnetron sputtering and post-annealed during 30 min at 300°C. Arrays of circular dots with diameters d = 200, 300 and 550 nm and a reference sample (diameter 1.7mm) were made of the film by electron lithography and Ar ion milling. After structural analysis by X-ray diffraction (XRD) and characterization by magnetization measurements and magnetic force microscopy, all samples were further annealed during 30min at 600°C. The XRD scans show that this led to an improvement of the crystalline quality in all samples, to a degree depending on the size of the dots. Both the structural and magnetic measurements imply that after the second heat treatment all samples have the easy magnetocrystalline direction (c-axis) mainly in the plane of the film, while the initial structures were characterized by a random distribution of c-axes