A thin carbon underlayer can promote the growth of the c axis of Co86Cr12Ta2 film perpendicular to the film surface at a much thinner stage. A smaller lattice constant c of the hcp structure was observed for Co86Cr12Ta2 thin-film media on a sputtered carbon underlayer. High substrate temperature increases the perpendicular coercivity of the Co86Cr12Ta2 film significantly. This increase is due to the decrease in the c/a ratio of Co hcp lattices. © 1997 American Institute of Physics.