A series of approximately 40 nm thick Co80Pt20 thin films have been sputter-deposited onto a combination of Ta, Pt and Ru underlayers grown at different layer thicknesses. The addition of a Ta seed layer to the Pt and Ru underlayers caused the {0002} hexagonal close packed (hcp) Co80Pt20's c-axis dispersion's full width at half maximum to narrow from approximately 12 degrees to approximately 2 degrees. In-situ stress measurements taken during deposition showed that the Ta seed layer reduced the growth stresses for the Pt and an initial 1 nm of growth for the Ru underlayers. The Ru layer thickness controlled the c/a ratio of the hcp Co80Pt20 film which regulated the degree of magnetic easy-axis alignment in the Co80Pt20 film. The optimal underlayer material stack for Co80Pt20 with a narrow c-axis dispersion and a high degree of magnetic easy-axis alignment was 5 nm Ta/10 nm Pt/5 nm Ru. (C) 2010 Elsevier B.V. All rights reserved.