Multiphysics program for ion-induced collision cascades and thermally activated phase separation: intermetallic nanolayers by interface mixing


Multiphysics program for ion-induced collision cascades and thermally activated phase separation: intermetallic nanolayers by interface mixing

Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.

Recent developments in computational materials modelling methods have to provide a qualitatively new level of predictive power and insight into materials design. In nature, different physical processes govern simultaneously the evolution of systems. Due to the complexity of the individual processes, so far their simulations are performed separately. One key to computational progress is the multiphysical treatment in a single computer program package.
Here, we consider the evolution of interfaces under energetic ion irradiation. There, the physical process of collisional mixing is in competition with thermally activated diffusion and phase separation. We developed a novel program which treats both physical processes simultaneously. The 3D atom relocations were calculated in the Binary Collision Approximation (BCA), whereas the thermally activated relaxation of energetic, atomic configurations as well as diffusive processes, were simulated by a very efficient bit-coded kinetic 3D Monte Carlo code. Contrary to molecular dynamics simulations, our approach allows studies on experimental spatiotemporal scales.
As applications we present two extremes of interface mixing: (i) Irradiation of interfaces made by immiscible elements, here Al and Pb, with He ions causes ballistic interface mixing accompanied by phase separation. Al and Pb clusters, which form in the interface region, show self-ordering. (ii) Irradiation of interfaces made by metals which form intermetallics, here Pt and Co, with He ions causes the formation of nanometric intermetallic layers with the sequence Pt/Pt3Co/PtCo/PtCo3/Co across the former interface. In the element mapping perpendicular to the interface (e.g. by RBS measurements), this results in step-wise changes of Pt/Co concentrations. Novel magnetic properties of such sandwiched phases are expected. In particular, a very interesting magnetic behaviour of irradiated Pt/Co/Pt multilayers has been observed. It can be shown that the transition between out of plane and in-plane magnetic anisotropy can be triggered by ion beam irradiation, whereas computer experiment can be useful for understanding the physical mechanism.

Keywords: BCA; kinetic Monte-Carlo; collision cascade; ion irradiation; interface mixing; phase seperation; phase ordering; intermetallics

  • Lecture (Conference)
    COSIRES 2010, 19.-23.07.2010, Collegium Maximum Auditorium in Kraków, Poland

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Publ.-Id: 14797