Influences of the substrate strain on microstructures of L1₀ FePt-X thin films by using phase field simulation

The microstructure evolution of the FePt-X (segregant) thin films is studied by employing a two-dimensional phase field model based on the elastic effect. Simulated results show that the lattice mismatch between the FePt-X thin film and substrate leads to slight rafting (preferential coarsening) of columnar FePt grains along the direction of the misfit strain, and produces more rounded grains, while an amorphous segregant is doped. The elastic energy primarily affects the areas between the FePt grains, where more than 90% of the elastic energy is concentrated. Moreover, the elastic energy is relaxed gradually with the formation of columnar periodic arrays of FePt grains. To generate columnar FePt grains microstructure in the FePt-X thin films, the lattice mismatch between the thin film and substrate should be controlled within 3% when the thermal expansion difference between the thin film and substrate is ignored.