L1 $_{0}$ FePt: Ordering, Anisotropy Constant and Their Relation to Film Composition

The L1
₀
phase in FePt films with compositions in the range of 47-50 at.%Pt is found to form more readily (lower kinetic ordering temperatures), to have a higher degree of tetragonality (lower c/a), to be more perfectly ordered (higher values of the order parameter) and to have higher values of magnetocrystalline anisotropy constant compared to compositions outside of this range. It is argued that the ease of L1
₀
formation, as measured by the kinetic ordering temperature, and the more perfect ordering of the L1
₀
phase, as measured by the order parameter, are related to the higher atomic mobilities in films with compositions in this optimal range. Comparison of experimental results from isothermal kinetic experiments with predicted results using kinetic data from nonisothermal experiments and different assumptions regarding the nucleation of the L1
₀
phase shows that the L1
₀
formation kinetics is best described by growth from a fixed density of preexisting nuclei (athermal nucleation).