[en] By cosputtering Ag with FePt on a Cr₉₀Ru₁₀ underlayer, the film texture and magnetic easy axis were successfully changed from the perpendicular to the longitudinal direction. The crystallographic structure and magnetic properties of Ag-doped FePt thin films were investigated. Doping of Ag in FePt films led to greater in-plane coercivity and smaller magnetic grain size. The in-plane coercivity of the nanocomposite films varied from 0.8 to 6.5 kOe, depending on the Ag content. With an increase in Ag content, the FePt grain size became smaller, and the magnetic reversal mechanism approached the nucleation mode. These results suggest a practical way by which to fabricate L1₀ FePt thin films with longitudinal anisotropy using a nanocomposite approach