Formation of Phases in the FePt/Au/FePt Films and their Magnetic Properties
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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.
Keywordsfilm ordered L10-FePt phase hydrogen annealing coercivity
The authors would like to thank Professor M. Albrecht and staff of the University of Augsburg (Germany) for preparing the samples, assisting in the research, and discussing the findings. This research effort was funded under the DAAD Leonard Euler Scholar Program (Grant DAAD No. 57198300 and Grant DAAD No. 57291435).
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