L10-ordering kinetics in FePt nano-layers: Monte Carlo simulation

“Order-order” kinetics in L10-ordered FePt nano-layers have been studied by Monte Carlo (MC) simulation implemented with Glauber dynamics and vacancy atomic-jump mechanism. In the presented preliminary approach the effects of the substrate character and of the tetragonal distortion of the superstructure were neglected. Atomic pair-interaction energies in two co-ordination shells were evaluated on the basis of Cluster-Expansion “ab initio” calculations carried out for Fe-Pt binary system. Nano-layers limited by two (0 0 1)-type free surfaces were simulated by imposing two-dimensional (x-y) periodic boundary conditions upon a sample of FePt with different variants of L10 superlattice (different orientations of monoatomic planes). Selective effect of free surfaces on the stability of L10 variants was observed. While no effect was detected in the case of the variants with (1 0 0)- and (0 1 0)-type Fe and Pt planes (x- and y-L10 variants, respectively), the L10 stability was strongly reduced in the case of z-L10 variant ((0 0 1)-type monoatomic planes). As a result, the initially homogeneous FePt films ordered in z-L10 variant showed a complex “order-order” process resulting in a microstructure of x- and y-L10 variant domains. Kinetics of the process was analysed in atomistic scale.