Percolation and magnetism: interplay and relevance

Magnetism of artificial structures, multilayer arrays and granular systems has lately attracted wide attention. On the contrary, the concept of percolation, first introduced in 1957, has scarcely been related to the former, in spite of the fact that it has been applied to many problems in completely different fields. In physics, percolation has been useful to study both macroscopic and microscopic phenomena, such as the electrical conduction of a mixture and the localization and hopping of electrons, respectively. However, recent experimental studies of magnetic granular solids have clearly established a connection between percolation and magnetism. In fact, magnetic anomalies were observed in a percolating system where the coercivity Hc of Ni films exhibits a non-monotonic behavior, related to topological morphology changes, which coincides with the onset of percolation. In this contribution we propose a theoretical model that describes the behavior of the coercivity Hc, of granular Ni films, as a percolation phenomenon. We show that the non-monotonic dependence of Hc, as a function of the occupation probability p, is due to the interplay of percolation and magnetism. Moreover, we also explain the dependence of Hc as a function of external magnetic field orientation