Seed Layer Effect on the Magnetic Properties of Ultrathin Co/Pt Multilayers With Perpendicular Magnetic Anisotropy

The effect of four different seed layers-Ru, Hf/Ru, Ru/Hf, and Hf on the magnetic properties of [Co 5/Pt 3 Å] multilayer (ML) stack with perpendicular magnetic anisotropy was investigated. The structural quality of the ML stacks was studied and correlated with the magnetic properties. Among the abovementioned seed layers, Ru promotes stronger fcc (111) texture in the ML due to less lattice mismatch (8% between Ru and Co) in Co/Pt MLs. As a result, higher anisotropy field (H_K ~ 17 kOe) and larger effective perpendicular anisotropy (K_eff ~ 1.2 × 10⁷ erg/cm³) were achieved for the MLs on Ru seed layer compared with other seed layers after annealing at 300 °C for 30 min. The perpendicular magnetic anisotropy of the MLs is improved at higher annealing temperature up to 400 °C for Ru and Hf/Ru seed layer. For the Co/Pt MLs on Ru, 1.3 × 10⁷ erg/cm³ perpendicular magnetic anisotropy was obtained even after annealing at 400 °C. Detail investigations of postannealing stability of the ML films on different seed layers were also discussed. The magnetic properties and structural properties of the films on four different seed layers were characterized after rapid thermal annealing process at 300 °C, 350 °C, and 400 °C for 30 min annealing duration. The high temperature endurance limit up to 400 °C for 30 min of the Co/Pt MLs on Ru and Hf/Ru seed layers makes them compatible with the back-end-of-line process temperature.