Combined nano- and mesoscale simulation of chemical ordering kinetics in nano-layered L1₀ AB binary intermetallics was performed. In the nano- (atomistic) scale Monte Carlo (MC) technique implemented with vacancy mechanism of atomic migration and diverse models for the system energetics were used. The meso-scale microstructure evolution was, in turn, modelled by means of a Monte Carlo procedure simulating antiphase-domain-boundary motion as controlled by antiphase-boundary energies evaluated within the nano-scale simulations. The study addressed FePt thin layers considered as a material for ultra-high-density magnetic storage media and revealed metastability of the L1₀ c-variant superstructure with monoatomic planes parallel to the layer surface and off-plane easy magnetization. The layers, originally perfectly ordered in a c-variant of the L1₀ superstructure, showed homogeneous disordering running in parallel with a spontaneous re-orientation of the monoatomic planes leading to a mosaic microstructure composed of a- and b-L1₀-variant domains. The domains nucleated heterogeneously on the free surface of the layer and grew discontinuously inwards its volume. Finally, the domains relaxed towards an equilibrium microstructure of the system. Two “atomistic-scale” processes: (i) homogeneous disordering and (ii)  nucleation of the a- and b-L1­₀-variant domains showed characteristic time scales. The same was observed for the meso-scale processes: (i) heterogeneous L1₀-variant domain growth and (ii) domain microstructure relaxation. The above complex structural evolution modelled by means of the multiscale Monte Carlo simulations has recently been observed experimentally in epitaxially deposited thin films of FePt [1].

[1]  M. Rennhofer, B. Sepiol, G. Vogl, M. Kozlowski, R. Kozubski, B. Laenens, A. Vantomme, J. Meersschaut,  Diffusion Fundamentals 6 (2007) 45.1 - 45.2