Size and polydispersity effect on the magnetization of densely packed   magnetic nanoparticles
  The magnetic properties of densely packed magnetic nanoparticles (MNP) assemblies are investigated from Monte Carlo simulations. The case of iron oxide nanoparticles is considered as a typical example of MNP. The main focus is put on particle size and size polydispersity influences on the magnetization curve. The particles are modeled as uniformly magnetized spheres isolated one from each other by a non magnetic layer representing the organic coating. A comparison with recent experimental results on $\gamma-$Fe$_2$O$_3$ powder samples differing by their size is given. 
Vincent Russier, Caroline de Montferrand, Yoann Lalatonne and Laurence   Motte
cond-mat.mtrl-sci