Structure and magnetic properties of 300-nm-thick FePt films with Hf underlayer

•10-nm-thick Hf underlayer promotes the ordering of 300-nm-thick FePt film.•Hf underlayer refines grain and magnetic domain sizes of FePt film.•Hf underlayer enhances permanent magnetic properties of FePt film.•High (BH)max is achieved for FePt/Hf thick films at reduced Ta=500–600 °C.

Structure, microstructure, magnetic properties of 300-nm-thick FePt films with 10-nm-thick Hf underlayer have been studied. The experimental results showed that the very thin Hf underlayer could promote the ordering at reduced temperatures by facilitating the nucleation of the order phase, leading to refined grain size and magnetic domain size. Therefore, the permanent magnetic properties of FePt films were enhanced. (BH)max and Hc of FePt films were greatly enhanced from 5.0–21.0 MGOe and 1.4–11.0 kOe for single layer to 10.2–23.6 MGOe and 4.5–13.2 kOe for Hf-underlayered films annealed in Ta region of 400–600 °C, respectively. Nevertheless, the severe interdiffusion between the Hf and FePt layers at Ta=800 °C resulted in the decreased S, coarsened surface morphology, grain and magnetic domain sizes, and therefore the slightly decreased (BH)max to 18.0 MGOe.