Abstract : Ferromagnetic materials are widely used in the industry. In the framework of the micromagnetic model introduced by Brown (1940), we study the influence of a thin nonmagnetic spacer on a ferromagnetic body. The evolution problem is modeled by the Landau-Lifshitz equation. We take into account phenomena on the surface of the spacer: super-exchange and surface anisotropy. We solve the existence problem for this equation with the surface terms. We then establish rigorously an equivalent boundary condition which models the thickness of the spacer on a domain with a thickless spacer. We compute some equilibrium states and the ultrafrequency susceptibility of some configurations. In a second stage, we homogenize the Landau-Lifshitz equation in both perforated and multilayers domains.