Fe-Ni-Pt thin films with compositions within the L1(0) ordered phase field were prepared by electrode-position and thermal annealing. The control of the film composition has been demonstrated in terms of its variation under different electrochemical conditions. It was found that while the underpotential codeposition (UPCD) of Pt with either Fe or Ni is in effect during the deposition process, the anomalous codeposition between Fe and Ni is not. Isothermal annealing experiments were conducted to investigate the kinetics of the formation of the L1(0) phase. The control of the film composition allows us to clarify the effects of replacing one element by another, particularly upon the ordering kinetics, the crystal structure, the phase separation behavior, and the magnetic properties. Temperature-dependent magnetic properties of the system were characterized to demonstrate the suitability of Fe-Ni-Pt for heat-assisted magnetic recording (HAMR). (C) 2019 Elsevier Ltd. All rights reserved.