Effect of oxygen contents on CoPt and FePt thin films

Autor: Yi-Jing Wu, 吳宜靜
Rok vydání: 2010
Druh dokumentu: 學位論文 ; thesis
Popis: 98
In our research, we have shown that the structure and magnetic properties of CoPt and FePt thin film. First,we used ultrahigh vacuum (UHV) magnetron sputtering system to prepare for CoPt and FePt thin films. Second, we capped CoPt and FePt with TiOx and SiOx layers by use of dual ion-beam deposition technique with the mixture of O2/Ar gas varied from 0% to 41%O2/Ar. Third, samples were annealed in the UHV chamber under different heat treatment condition. Finally, we did a series of analysis to investigate the effect of annealing temperature and top oxide on microstructure and magnetism in CoPt and FePt thin films. The coercivity of as-deposited SiO2/CoPt/TiOx is about Hc⊥~205 to 242 Oe and Hc//~35 to 54 Oe. The magnetic property mainly comes from soft magnetic phase Co. After annealing at 600oC for 20 mins, the in-plane coercivity is about Hc//~191 to 407 Oe. And TEM results show phase transformation to orderded fct phase. However, the structures show continuous thin films, which means that Ti and O do not diffuse into CoPt thin film to separate grains during post-annealing. The coercivity of as-deposited SiO2/CoPt/SiOx is about Hc⊥~106 to 277 Oe ; Hc//~39 to 67 Oe. After annealing at 600oC for 20 mins, the in-plane coercivity is about Hc//~127 to 348 Oe. SiO2/FePt/TiOx (30%O2/Ar) shows that phase transformation to ordered fct phase at 400oC. From TEM analysis, grain sizes become smaller because of grains separation by Ti and O atoms at 650oC; ordering parameter and coercivity are 0.74 and Hc⊥=11.4 kOe,Hc// =11.7 kOe,respectively. In SiO2/FePt/TiOx(0~41%O2/Ar)，phase transformation to ordered fct phase after annealing at 550oC for 10 mins. 21%O2/Ar shows largest perpendicular coercivity(Hc⊥ ~14.8 kOe). The lattice constant(a~3.80Å, c~3.70 Å) after annealing does not change with %O2/Ar, which means that TiOx does not diffuse into FePt lattice. Lastly,we use MgO(001) substrate to replace SiO2 substrate and preparing FePt/TiOx and FePt/SiOx (30%O2/Ar). After annealing,MgO(001)/FePt/TiOx shows Hc⊥~8.51kOe and Hc//~0.81 kOe and MgO(001)/FePt/SiOx shows Hc⊥~6.71kOe and Hc//~2.84 kOe. The ordering parameter is approximately 0.7. From δM analysis, after post-annealing, the curve of MgO(001)/FePt/TiOx and MgO(001)/FePt/SiOx show negative peak, indicating that the predominant interparticle interactions are dipolar. These indicate that grains may be separated after annealing.
Databáze: Networked Digital Library of Theses & Dissertations
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