Improvement of chemical ordering of FePt (001) oriented films by MgO buffer layer

Chemically ordered $L10$ FePt layer was obtained at temperature as low as $280°C$ by in situ heating by using MgO buffer layer on CrRu (200) underlayer. The chemical ordering and magnetocrystalline anisotropy, $Ku$⁠, increased with increasing deposition temperature from $280to400°C$⁠. The out-of-plane coercivity $Hc⊥$ also increased significantly from $2.7to9.0kOe$⁠. All the films showed perpendicular anisotropy. The reason for the increase in the coercivity was investigated by reducing the thickness of the FePt layer to $4nm$ and varying the thickness of the MgO buffer layer at 1, 2, and $4nm$⁠. Well isolated FePt islands were formed. When the MgO layer was $1nm$⁠, the $Hc⊥$ of the $4nm$ FePt layer was as high as $12kOe$⁠. However, it reduced to $6.3kOe$ when the MgO was $4nm$⁠. The change in $Hc⊥$ was due to the improved chemical ordering and thus higher magnetocrystalline anisotropy.