  We present a numerical study of the magnetic structure of nanostructured iron
fluoride, using the Monte-Carlo-Metropolis simulated annealing technique and a
classical Heisenberg Hamiltonian with a superexchange angle dependence. The
parameters are adjusted on experimental results, and the atomic structure and
topology taken from a previous atomistic model of grain boundaries in the same
system. We find perfect antiferromagnetic crystalline grains and a disordered
magnetic configuration (speromagnetic like) at the grain boundary, in agreement
with experimental findings. Both the lowest magnetic energy and the rate of
magnetic frustration are found to be dependent on the relative disorientation
of crystalline grains, i.e. on the cationic topology. By simulating hysteresis
loops, we find that the magnetization rotation is not spatially uniform. We
conclude on possible extensions of the model.
