Large Uniaxial Magnetic Anisotropy of Co–Pt Perpendicular Films Induced by Lattice Deformation

A study of the thickness dependence of the uniaxial magnetic anisotropy Kuof 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 Kuon reducing the film thickness, which was previously reported for Co80Pt20/Ru films. Kuincreased significantly as the thickness decreased in all series of films with various Pt content. The rate of increase of Kuwith reducing thickness became increasingly large as the Pt content decreased. It should be noted that the Kuof 2-nm-thick films was an almost constant 2times107erg/cm3over the range of Pt contents studied, although Kuwas maximized at 25-30at%Pt content for films thicker than 5 nm. Experimental results suggest that the increase in Kuon reducing the thickness was mostly related to a reduction of the hcp Co-Pt lattice c/a ratio