Exchange interaction between a ferromagnetic substrate and adsorbed metallo-porphyrin molecules

Exchange coupling between a magnetized thin film cobalt on mica substrate and adsorbed manganese(III)-tetraphenyl-porphyrin chloride (MnTPPCl) molecules is studied by X-ray magnetic circular dichroism. In the regime of a submonolayer coverage of MnTPPCl a clear circular dichroism is observed at the Mn L_III,II-edge, which is reverted with opposite grazing incidence with respect to the spin moments in the cobalt film. This result shows that the two species are ferromagnetically coupled to each other. Further evidence for the role of exchange interaction as the primary cause of the induced magnetism in MnTPPCl is observed on hysteresis loops of Co and MnTPPCl.