The magnetic properties of Fe38Pt62 and Fe52Pt48 films sputter deposited on MgO (001) substrates with and without a buffer layer at the substrate temperature Ts of 300 °C have been investigated. Pt, Au, and PtAu alloys with different compositions were used as the buffer layer to study the influence of the lattice mismatch between the FePt layer and the buffer layer. The L10 ordered structure with large perpendicular magnetic anisotropy has been obtained for the Fe38Pt62 films irrespective of the buffer layer. The degree of long-range order S and uniaxial magnetic anisotropy energy Ku increase with increasing the lattice mismatch, and S and Ku show maxima of 0.8±0.1 and 2.7×107 erg/cm3, respectively, for the film without a buffer layer. For Fe52Pt48 films, on the other hand, the L10 ordered structure with perpendicular magnetic anisotropy has been obtained only for the film with an Au buffer layer. © 2004 American Institute of Physics.