| Summary: | 博士 === 逢甲大學 === 材料科學所 === 93 === FePt and FePt/Cu thin films were fabricated by magnetron sputtering on quartz substrates. Effects of thickness and annealing temperature on magnetic properties were studied. The thickness of FePt ranged from 10 nm to 200 nm. For single-layer FePt, the optimum condition of magnetic properties appeared at a thickness of 60 nm. The ordering parameter (K) increases with temperatures and reaches a maximum value 0.9 at annealing temperature of 800℃. The high K value is an important reason for the high coercivity.
In the FePt (60 nm)/Cu (60 nm) thin films, we found that the maximum coercivity appeared as the sample was annealed at 400℃. In this condition, interfacial diffusion is mainly through the FePt grain boundary. For the higher annealing temperature, the volume diffusion took place. XRD patterns of FePt/Cu films showed that FePt and Cu extensively formed a ternary solid solution at higher annealing temperature (＞500℃) which decreases the coercivity to a few hundreds of oersteds. The analyses of δM plots showed that the diffusion of Cu in FePt grain boundaries reduces the exchange coupling as the thin films was annealed at 400℃.
In the FePt/Au thin films, we found that the coercivity increased dramatically with the annealing temperature. The maximum coercivity of 30 kOe appeared at the FePt (10 nm)/Au (60 nm) sample. From the results of XRD study, we learned that even at a very high temperature annealing, no volume diffusion can be found in both FePt and Au grains. The interdiffusion of FePt and Au also forms a nanocomposited microstructure consisting of FePt particles embedded in Au matrix. This microstructural modification also leads the reversal behavior changed from the domain wall motion to the nucleation control.
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