Physical analysis of the through-ligand long-distance magnetic coupling: spin-polarization versus Anderson mechanismAuthors: T. Terencio (a) , R. Bastardis (b) , N. Suaud (a) , D. Maynau (a) , J. Bonvoisin (c) , J.P.Malrieu (a) , C. J. Calzado (d) and N. Guihéry (a) Affiliations:(a AbstractThe physical factors governing the magnetic coupling between two magnetic sites are analyzed and quantified as functions of the length of the bridging conjugated ligand. Using wave-function-theory based ab initio calculations, it has been possible to separate and calculate the various contributions to the magnetic coupling, i.e. the direct exchange, the spin polarization and the kinetic exchange. It is shown on model systems that while the Anderson mechanism brings the leading contribution for short-length ligands, the spin polarization dominates the through-long-ligand couplings. Since the spin polarization decreases more slowly than the kinetic exchange, highly spin polarizable bridging ligand would generate a good magneto-communication between interacting magnetic units. 2 I IntroductionThe electronic communication between two magnetic sites connected through bridges has been a topic of large interest in molecular electronics [1][2][3][4] and spintronics [5,6]. Much effort from experimentalists has been invested in the elucidation of the role of extended bridges between two interacting units, both concerning the electron transfer in mixed valence compounds (electro-communication) and the magnetic coupling of unpaired electrons in pure magnetic compounds (magneto-communication).From a theoretical point of view, several works reviewed in references [7,8] Furthermore, the separation of both mechanisms enables us to quantify all effective interactions involved in the magnetic coupling, i.e. direct exchange, spin polarization, hopping integral t and on-site electron repulsion U.In section II, the various physical factors governing the magnetic interaction are briefly summarized and the methodology required to accurately reproduce them is recalled. Section III is devoted to an ab initio study of the different contributions to the magnetic coupling as