The formation of L1(0) FePt nanoparticles by annealing of FePt/C multilayer films was studied. After annealing at 550degreesC for 30 min, the superlattice peaks (0 0 1) and (1 10) found in the X-ray diffraction pattern of the FePt/C films indicate that the face-centered cubic disordered phase has been partially transformed into the L1(0) phase. FePt/C thin films became magnetically hard with a coercivity in the range 1.8-9.2 kOe due to the high anisotropy energy associated with the L1(0) ordered phase. The coercivity of the films decreased rapidly with increasing C layer thickness. With increasing C content, the grain size and intergrain interaction of the FePt/C multilayer films decreased. The coercivity not only depends on the C content, but also on the structure of the FePt/C mutilayer. The [FePt 3 mm/C 3 nm](10) sample shows a small dipolar interaction. (C) 2004 Elsevier B.V. All rights reserved.