Magnetic properties and microstructure of FePt/GePt bilayer

We explored the island-like Ge3Pt2 underlayer effect and post-annealing temperature on FePt magnetic properties and microstructure. The Ge3Pt2 intermetallic compound was formed at high annealing temperature (≥600 °C) and the island-like structure was occurred to relax the growth stress between Ge3Pt2 and quartz. After island-like underlayer, the L10 FePt film was deposited on Ge3Pt2 islands or quartz substrate simultaneously. After deposition, the GePt/FePt bilayer post-annealing at 400 °C for 1 h, the higher degree of ordering (S = 0.86) and coercivity (Hc = 8.8 kOe) than single layer FePt film (Hc = 6.4 kOe) were measured. This suggests that there is a surface morphology dependence on the coercivity of FePt film. During post-annealing, the island-like Ge3Pt2 induced tensile stress on FePt, which enhanced the formation of ordered FePt. In comparison, when the post-annealing up to 800 °C for 1 h, the FePt ordering was suppressed (S = 0.75) and the coercivity was down to 3.6 kOe. It is due to the interface diffusion between GePt and FePt at 800 °C. The irregular isolated GePt/FePt islands were formed on quartz substrate. As a result, the Ge3Pt2 compound was good for underlayer of FePt film with low post-annealing temperature (400 °C).