Formation of Phases in the FePt/Au/FePt Films and their Magnetic Properties

The effect of annealing atmosphere (vacuum, hydrogen) and intermediate Au layer thickness on the formation of a magnetically hard L10 phase and the magnetic properties of Fe50Pt50(15 nm)/Au(7.5, 30 nm)/Fe50Pt50(15 nm) films deposited by magnetron sputtering onto SiO2(100 nm)/Si(001) substrates was studied. Samples were heat-treated in a hydrogen atmosphere at 100 kPa. The disordered A1-FePt phase formed in the as-deposited films. The ordered L10-FePt phase appeared in the film with an intermediate Au (7.5 nm) layer during vacuum annealing at 650°C. Increase in the intermediate Au layer thickness to 30 nm reduces the ordering temperature to 600°C. This is promoted by higher compressive stresses in the as-deposited Fe50Pt50 layers with a thicker Au interlayer. In hydrogen annealing, the A1 → L10-FePt phase transition in the Fe50Pt50(15 nm)/Au(7.5, 30 nm)/Fe50Pt50(15 nm) films starts at 500°C regardless of the intermediate Au layer thickness. The Au and FePt axial (111) textures are observed in the films annealed in hydrogen. This is more evident in the films with a thicker Au (30 nm) interlayer. The film with an intermediate Au (30 nm) layer shows 27.3 kOe coercivity after vacuum annealing at 900°C. The same coercivity can be achieved by hydrogen annealing at 700°C, which is 200°C lower than after vacuum annealing due to the introduction of hydrogen into voids of the L10-FePt lattice and increase of stresses.