L1 0-ordering kinetics in FePt nano-layers: Monte Carlo simulation

Abstract

“Order–order” kinetics in L1 0-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 L1 0 superlattice (different orientations of monoatomic planes). Selective effect of free surfaces on the stability of L1 0 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-L1 0 variants, respectively), the L1 0 stability was strongly reduced in the case of z-L1 0 variant ((0 0 1)-type monoatomic planes). As a result, the initially homogeneous FePt films ordered in z-L1 0 variant showed a complex “order–order” process resulting in a microstructure of x- and y-L1 0 variant domains. Kinetics of the process was analysed in atomistic scale.