Substantial reduction in coercivity of perpendicular CoPt/FePt graded films with near-atomic flatness on glass substrates

Perpendicular graded films comprising soft Co66Pt34 layer and hard L10-FePt layer deposited on glass substrates were investigated. Microstructure observations reveal the unidirectional growth of the CoPt layer on (0 0 1) FePt film. By controlling the deposition temperature of soft layer and interlayer diffusion, the substantially reduced coercivity (Hc) and the near-atomic flatness of surface morphology are simultaneously obtained. In comparison to the single-layered FePt, Hc of the optimal graded film is significantly reduced by a factor of 4, while the surface roughness of the graded film lower than 0.3 nm is obtained. Depth-resolved techniques prove that the gradation of L10 ordering could lead to the reduction of Hc and switching field distribution due to the enhancement of interlayer exchange coupling. Well exchange-coupled graded films are characterized at a soft layer thickness within 20 nm.