Effect of Underlayer Structures on Microstructures and Magnetic Properties of Co-Rich Co-Pt Films Prepared at Ambient Temperature

Granular Co-rich Co-Pt nanograins having perpendicular coercivity (Hc_⊥) of 4.0 kOe and perpendicular squareness (S_⊥) of 0.75 can be achieved by depositing Co₈₀Pt₂₀ (25 nm) film onto Ru (30 nm)/Ag (100 nm) bilayer films using an argon pressure of 5 mTorr to deposit an Ag underlayer at ambient temperature. However, it is found that the Co₈₀Pt₂₀ film deposited directly onto an Ru layer without an Ag underlayer shows in-plane magnetic anisotropy. This is because an fcc Ag (111) underlayer can enhance the hcp Ru (0002) seed layer, inducing (0002) texture in the hexagonal Co₈₀Pt₂₀ magnetic layer, leading to the perpendicular magnetic anisotropy of Co₈₀Pt₂₀ films. TEM images show that granular nanograins with an average size of 8.0 nm can be observed in the Co₈₀Pt₂₀ magnetic layer.