Large uniaxial magnetic anisotropy by lattice deformation in CoPt/Ru perpendicular films.

A large uniaxial magnetic anisotropy K_u of about 2×10⁷ erg/cm³ was obtained in Co–(20–30) at. % Pt perpendicular films deposited on Ru seed layers. The films showed good c-axis orientation perpendicular to the film plane, and no evidence of a Co₃Pt-type-ordered structure was found in the X-ray-diffraction patterns. The value of K_u (the sum of the first- and second-order terms of uniaxial anisotropy, K_u1 and K_u2) increased as the thickness of the CoPt layer decreased, and reached about 2×10⁷ erg/cm³ at 2 nm (Co–20 at. % Pt films) or 5 nm (Co–(25–30) at. % Pt films). The ratio of K_u2 to K_u1 was 0.16 in 40 nm films, but reduced to less than 0.03 for thicknesses below 5 nm. The experimental results suggest that, besides the surface anisotropy, the increase in K_u on reducing the thickness is mostly related to the reduction of the hcp-CoPt lattice c/a ratio, probably due to epitaxial growth of CoPt on the Ru seed layer. [ABSTRACT FROM AUTHOR]