Magnetic atomistic modelling and simulation of nanocrystalline thin films

In this study, a methodology, for polycrystalline magnetic thin films construction composed by nano-grains, was developed. The size and shape of grains and samples under scale considerations of magnetic materials were developed, taking into account periodic boundary conditions. A comparative analysis of results obtained with experimental grains' distribution is presented. Lognormal distribution was proposed as a function of number of atoms per grain that agrees with experimental reports. A test of the magnetization as a function of the temperature was obtained by the parallelized Monte Carlo method dividing the sample in cells. The Hamiltonian considered variations of the exchange constant with atomic distance from RKKY approximation and a cubic magneto-crystalline anisotropy as a function of the temperature also was implemented. Results showed changes over critical behavior and different values for magnetization of saturation at low temperatures. Critical temperature is affected by the increments of disorder into the sample when grain size is reduced. A reduction of magnetization is correlated with mono-domain regimen in the sample for most of grains. These states are favored during the cooling process by the disorder in grain boundaries.