  Metal-polymer nanocomposites have been investigated extensively during the
last years due to their interesting functional applications. They are often
produced by vapor phase deposition which generally leads to the self-organized
formation of spherical metallic nanoparticles in the organic matrix, while
nanocolumns are only obtained under very specific conditions.
Experiments\cite{Grev+06} have shown that co-evaporation of the metallic and
organic components in a simple single-step process can give rise to the
formation of ultrahigh-density Fe-Ni-Co nanocolumnar structures embedded in a
fluoropolymer matrix. Here we present a kinetic Monte Carlo approach which is
based on an new model involving the depression of the melting point on the
nanoscale and a critical nanoparticle size required for solidification. In
addition we present new experimental results down to a deposition temperature
of \cel{-70} and also report the magnetic properties. The simulations provide a
detailed understanding of the transition from spherical cluster growth to
formation of elongated structures and are in quantitative agreement with the
experiments.
