Magnetic Properties and Microstructure of FeOx/Fe/FePt and FeOx/FePt Films

The Fe(6 nm)/FePt film with perpendicular magnetization was deposited on the glass substrate. To study the oxygen diffusion effect on the coupling of Fe/FePt bilayer, the plasma oxidation with 0.5 similar to 7% oxygen flow ratio was performed during sputtered part of Fe layer and formed the FeOx(3 nm)/Fe(3 nm)/FePt trilayer. Two-step magnetic hysteresis loops were found in trilayer with oxygen flow ratio above 1%. The magnetization in FeOx and Fe/FePt layers was decoupled. The moments in FeOx layer were first reversed and followed by coupled Fe/FePt bilayer. The trilayer was annealed again at 500 degrees C and 800 degrees C for 3 minutes. When the FeOx(3 nm)/Fe(3 nm)/FePt trilayer was annealed at 500 degrees C, the layers structure was changed to FeOx(6 nm)/FePt bilayer due to oxygen diffusion. The hard-magnetic FeOx(6 nm)/FePt film was coupled with single switching field. The FeOx/(disordered FePt) layer structure was observed with further annealing at 800 degrees C and presented soft-magnetic loop. In summary, the coupling between soft-magnetic Fe, FeOx layer, and hard-magnetic L1(0) FePt layer can be controlled by the oxygen diffusion behavior, and the oxidation of Fe layer was tuned by the annealing temperature. The ordered L1(0) FePt layer was deteriorated by oxygen and became disordered FePt when the annealed temperature was up to 800 degrees C.