Dot arrays of L1₀-type FePt ordered alloy perpendicular films fabricated using low-temperature sputter film deposition

Using ultrahigh vacuum sputter film deposition, we fabricated L1 ₀-type Fe₅₀Pt₅₀ ordered alloy perpendicular films on MgO(001) single-crystal substrates and 2.5 in. glass disks at low substrate temperatures of 200-350°C. Then we examined the magnetic properties of the dot arrays made from these films. The uniaxial magnetic anisotropy K_u for L1₀-type FePt films (10 nm in thickness) deposited with a Pd underlayer on MgO(001) substrates reached about 2 10 ⁷ erg/cm³ at the substrate temperature T_s of 200C, and 3 10⁷ erg/cm³ at T_s 250C. The order parameter S was about 0.46 at T_s 300C. Moreover, K_u for L1₀-FePt films fabricated on glass disks using MgO/Cr underlayers shows 3.4 10⁷ erg/cm³ at T_s 300C, which was almost equal to that for FePt single-crystal films deposited on Pd/MgO(001). The switching field distribution σ/H_c for dot arrays made from L1₀-FePt film [5 nm in thickness, on Pd/MgO(001) at T_s 250°C] was small; /H_c 0.11 for a dot diameter of 15 nm. This value was smaller than that of hcp-Co₇₅Pt₂₅ dot arrays (/H_c 0.18). The difference was mainly attributable to the degree of the easy axis distribution. This result demonstrates the homogeneous formation of a L1₀-type ordered structure in the FePt layers.