We have shown that the structural and magnetic properties of FePt thin films were affected strongly by capped SiO 2 layers prepared by ionbeam bombardment followed by post-annealing. Compared to the single fcc FePt phase in the as-deposited FePt/SiO 2 bilayer (0% O 2 /Ar), annealing at 550 C produced an ordered L1 0 FePt phase with enhanced coercivity ($14 kOe). Increasing the %O 2 /Ar during deposition of the top SiO 2 layer resulted in smaller ordered FePt grains separated by grain boundaries of SiO 2 . We find that the (001) diffraction peak is broadened considerably with larger SiO 2 deposition %O 2 /Ar and annealing, likely due to the induced strain. Our results indicate that FePt/ SiO 2 films deposited with lower %O 2 /Ar, the oxygen atoms created by the ion-beam bombardment act effectively to inhibit the FePt grain growth, whereas the excess oxygen atoms present during film deposition with higher %O 2 /Ar may induce a local strain on the FePt crystallites by occupying the interstitial sites in the FePt lattice.
The effects of the fabrication methods and different capped oxide (SiO(2) and TiO(2)) layers on the microstructure and magnetism of FePt thin films were studied. Both structural ordering (S similar to 0.7) from the fcc FePt phase to the fct FePt phase and magnetic hardening were observed in the annealed FePt/SiO(2) thin films with a low substrate rotation speed (S(r) = 1 rpm). However, only the annealed FePt/SiO(2) thin films prepared with a high S(r) (10 rpm) exhibited isolated FePt grains separated by the grain boundary SiO(2), as revealed by transmission electron microscopy and magnetometry. Furthermore, similar results in microstructures and magnetic properties were obtained after replacing the capped layer with TiO(2). However, an enhanced order parameter (S similar to 0.85) and a smaller FePt grain size (similar to 6.8 nm), which are promising characteristics for ultrahigh-density magnetic recording, were achieved in the annealed FePt/TiO(2) thin films; however, the annealed FePt/SiO(2) thin films exhibited a larger grain size (similar to 15 nm). This indicates that TiO(2) inhibits the grain growth of FePt more effectively than SiO(2). (C) 2010 The Japan Society of Applied Physic
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