| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 99 === In our research, we have shown that the structure and magnetic properties of FePt thin film. The co-sputtered FePt films were prepared by ultrahigh vacuum (UHV) magnetron sputtering system while the capping TaOx layer was prepared by using dual ion-beam deposition technique with mixture of O2/Ar gas that was varied from 0% to 41% O2/Ar. Samples were annealed in the UHV chamber under different heat treatment condition. Then, we did a series of analysis to investigate the effect of annealing temperature and top oxide on microstructure and magnetism in FePt thin films.
The structures of as-deposited single layer TaOx was deposited without feeding oxygen, ultra small Ta grains (about 2 nm) with bcc structure were obtained. With the increasing oxygen content, the TaOx were amorphous and at the 41% O2/Ar it appeared wave-like patterns due to too much oxide.
According to XRD, the structures of as-deposited FePt/TaOx (0% to 41% O2/Ar) consisted of fcc FePt (a ~ 3.81 A) phases that resulted from intermixing of Fe and Pt during deposition. The grain sizes ranged from 2 to 14 nm and the out-of-plane coercivity of the 15% O2/Ar was about 62 Oe.
After annealed 550oC for 10 mins, the structures of different oxygen content FePt/TaOx exhibit ordered L10 FePt phases. The highest ordering parameter (S~0.6) occured at 15% O2/Ar, and had the maximum out-of-plane coercivity( Hc⊥~ 4.2 kOe). It was also well separated FePt grains, proved by TEM and ESCA which indicated Ta-oxide could diffuse effectively into FePt layer. When the oxygen content above 21%, the ordering parameters are reduced with increasing oxygen. Especially, at 41% O2/Ar had minimum ordering parameter and the fcc phase coexisted with fct phase based on XRD (111) peaks.
In the part of different anneal temperature, FePt/TaOx 15% O2/Ar showed that phase transferred from fcc to fct structure at temperature greater than 400oC. The grains growth with increasing annealing temperature, the grains grew and combined together when the temperutare was 650oC that led to slightly reducing the magnetic properties (Hc⊥~3.6 kOe) and ordering parameter (S ~ 0.53).
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