Microstructures and Magnetism of Different Oxides Separating FePt Grains via Ion-Beam Bombardment and Annealing

The effects of the fabrication methods and different capped oxide (SiO2 and TiO2) layers on the microstructure and magnetism of FePt thin films were studied. Both structural ordering ($S \sim 0.7$) from the fcc FePt phase to the fct FePt phase and magnetic hardening were observed in the annealed FePt/SiO2 thin films with a low substrate rotation speed ($S_{\text{r}} = 1$ rpm). However, only the annealed FePt/SiO2 thin films prepared with a high $S_{\text{r}}$ (10 rpm) exhibited isolated FePt grains separated by the grain boundary SiO2, as revealed by transmission electron microscopy and magnetometry. Furthermore, similar results in microstructures and magnetic properties were obtained after replacing the capped layer with TiO2. However, an enhanced order parameter ($S \sim 0.85$) and a smaller FePt grain size (${\sim}6.8$ nm), which are promising characteristics for ultrahigh-density magnetic recording, were achieved in the annealed FePt/TiO2 thin films; however, the annealed FePt/SiO2 thin films exhibited a larger grain size (${\sim}15$ nm). This indicates that TiO2 inhibits the grain growth of FePt more effectively than SiO2.