The HRTEM cross-sectional lattice image shows that a well epitaxial growth of hcp Co-rich Co-Pt (002) on Pt(111) underlayer leads to good perpendicular magnetic anisotropy of Co-rich Co-Pt film. It is found that both the perpendicular coercivity (Hc(perpendicular to)) and perpendicular squareness (S(perpendicular to)) of Co-rich Co-Pt films without Pt capped layer are larger than that of Co-rich Co-Pt films with Pt capped layer. The cross-sectional TEM-EDS and AES analysis confirm that the oxygen atoms will diffuse from film surface into the Co-rich Co-Pt film without adding Pt capped layer, and it react with cobalt atoms to form CoO, which is detected by XPS analysis. The increase in perpendicular hard magnetic properties of Co-rich Co-Pt film without Pt capped layer is mainly due to form CoO in the Co-rich Co-Pt film. (c) 2009 Elsevier B.V. All rights reserved.