Formation of ordered L10-FePt phase in FePt–Ag thin films

In this work, the influence of an Ag layer, which is located at different positions of the layer stack (top, intermediate, bottom), on the structural and magnetic properties of ordered L10 phase in Fe50Pt50 films was investigated. It was found that the position of an additional Ag layer affects the stress state of the as-deposited FePt films. Mechanical stress is induced during deposition and post-annealing process due to the difference in thermal expansion coefficients and lattice mismatch of FePt, Ag, and substrate. The initial stress state affects the ordering process during subsequent heat treatment. The higher level of initial compressive stress (− 7.8 GPa) in FePt/Ag/FePt films results in L10 phase formation at a temperature of 700 °C which is about 100 °C lower than in films with Ag bottom (− 3.6 GPa) and top (+ 0.86 GPa) layers. A more pronounced (001) oriented growth of the L10 phase was observed in stacks with Ag top layer as compared to Ag bottom and intermediate layers. The highest values of coercivity were obtained for films with Ag intermediate and bottom layers, which is due to the distribution of Ag along FePt grain boundaries that result in strong exchange decoupling of FePt grains. Furthermore, the formation of the ordered L10 phase at comparatively low temperatures of about 370 °C was observed in a free-standing FePt/Ag (30 nm)/FePt film.