A Co3Pt magnetic layer with a thickness of 7-28 nm was deposited onto a Pt underlayer. As-deposited Co3Pt/Pt double-layered films with or without a 5 nm Pt capping layer were annealed at temperatures between 275 and 375 degrees C. The results show that the out-of-plane coercivity (H-c perpendicular to) of CO3Pt films without a Pt capping layer is larger than that of Co3Pt films with a Pt capping layer after annealing. The H-c perpendicular to of the film without a capping layer annealed at 300 degrees C increased as the thickness of the Co3Pt film increased, reaching a maximum H-c perpendicular to value at 18 nm. Also, an 85 nm thick Tb30Co70 film with high perpendicular magnetic anisotropy deposited on a Co3Pt (14 nm)/Pt(100 nm) double-layered film enhanced the H-c perpendicular to and out-of-plane squareness (S-perpendicular to) values of the Co3Pt film. (C) 2011 Elsevier B.V. All rights reserved.