The question may arise of how a limit of the system enlargement can be defined by the n parameter. As the super-cell should be magnetically uniform, its size should not exceed a critical diameter for which magnetization reversal takes place by coherent rotation. More precisely, based on the system parameters (J, S) one can determine a coherence radius Rcoh which is the maximum size of a uniformly magnetized particle [26]. For various magnetic materials, it ranges from more than 10 nm to even more than 1 µm for magnetically soft and hard magnets, respectively [27].