Large uniaxial magnetic anisotropy of Co-Pt perpendicular films induced by lattice deformation

A study of the thickness dependence of the uniaxial magnetic anisotropy K_u of Co-Pt perpendicular films deposited on Ru seed layers was extended over a wide range of Pt content from 10 to 30 at%, to further investigate the origin of the significant increase in K_u on reducing the film thickness, which was previously reported for Co₈₀Pt ₂₀/Ru films. K_u increased significantly as the thickness decreased in all series of films with various Pt content. The rate of increase of K_u with reducing thickness became increasingly large as the Pt content decreased. It should be noted that the K_u of 2-nm-thick films was an almost constant 2 × 10⁷ erg/cm³ over the range of Pt contents studied, although K_u was maximized at 25-30at%Pt content for films thicker than 5 nm. Experimental results suggest that the increase in K_u on reducing the thickness was mostly related to a reduction of the hep Co-Pt lattice c/a ratio.